btrfs: skip update of block group item if used bytes are the same

[sfrench/cifs-2.6.git] / fs / btrfs / block-group.c

// SPDX-License-Identifier: GPL-2.0

#include <linux/list_sort.h>
#include "misc.h"
#include "ctree.h"
#include "block-group.h"
#include "space-info.h"
#include "disk-io.h"
#include "free-space-cache.h"
#include "free-space-tree.h"
#include "volumes.h"
#include "transaction.h"
#include "ref-verify.h"
#include "sysfs.h"
#include "tree-log.h"
#include "delalloc-space.h"
#include "discard.h"
#include "raid56.h"
#include "zoned.h"

#ifdef CONFIG_BTRFS_DEBUG
int btrfs_should_fragment_free_space(struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;

        return (btrfs_test_opt(fs_info, FRAGMENT_METADATA) &&
                block_group->flags & BTRFS_BLOCK_GROUP_METADATA) ||
               (btrfs_test_opt(fs_info, FRAGMENT_DATA) &&
                block_group->flags &  BTRFS_BLOCK_GROUP_DATA);
}
#endif

/*
 * Return target flags in extended format or 0 if restripe for this chunk_type
 * is not in progress
 *
 * Should be called with balance_lock held
 */
static u64 get_restripe_target(struct btrfs_fs_info *fs_info, u64 flags)
{
        struct btrfs_balance_control *bctl = fs_info->balance_ctl;
        u64 target = 0;

        if (!bctl)
                return 0;

        if (flags & BTRFS_BLOCK_GROUP_DATA &&
            bctl->data.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_DATA | bctl->data.target;
        } else if (flags & BTRFS_BLOCK_GROUP_SYSTEM &&
                   bctl->sys.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_SYSTEM | bctl->sys.target;
        } else if (flags & BTRFS_BLOCK_GROUP_METADATA &&
                   bctl->meta.flags & BTRFS_BALANCE_ARGS_CONVERT) {
                target = BTRFS_BLOCK_GROUP_METADATA | bctl->meta.target;
        }

        return target;
}

/*
 * @flags: available profiles in extended format (see ctree.h)
 *
 * Return reduced profile in chunk format.  If profile changing is in progress
 * (either running or paused) picks the target profile (if it's already
 * available), otherwise falls back to plain reducing.
 */
static u64 btrfs_reduce_alloc_profile(struct btrfs_fs_info *fs_info, u64 flags)
{
        u64 num_devices = fs_info->fs_devices->rw_devices;
        u64 target;
        u64 raid_type;
        u64 allowed = 0;

        /*
         * See if restripe for this chunk_type is in progress, if so try to
         * reduce to the target profile
         */
        spin_lock(&fs_info->balance_lock);
        target = get_restripe_target(fs_info, flags);
        if (target) {
                spin_unlock(&fs_info->balance_lock);
                return extended_to_chunk(target);
        }
        spin_unlock(&fs_info->balance_lock);

        /* First, mask out the RAID levels which aren't possible */
        for (raid_type = 0; raid_type < BTRFS_NR_RAID_TYPES; raid_type++) {
                if (num_devices >= btrfs_raid_array[raid_type].devs_min)
                        allowed |= btrfs_raid_array[raid_type].bg_flag;
        }
        allowed &= flags;

        if (allowed & BTRFS_BLOCK_GROUP_RAID6)
                allowed = BTRFS_BLOCK_GROUP_RAID6;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID5)
                allowed = BTRFS_BLOCK_GROUP_RAID5;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID10)
                allowed = BTRFS_BLOCK_GROUP_RAID10;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID1)
                allowed = BTRFS_BLOCK_GROUP_RAID1;
        else if (allowed & BTRFS_BLOCK_GROUP_RAID0)
                allowed = BTRFS_BLOCK_GROUP_RAID0;

        flags &= ~BTRFS_BLOCK_GROUP_PROFILE_MASK;

        return extended_to_chunk(flags | allowed);
}

u64 btrfs_get_alloc_profile(struct btrfs_fs_info *fs_info, u64 orig_flags)
{
        unsigned seq;
        u64 flags;

        do {
                flags = orig_flags;
                seq = read_seqbegin(&fs_info->profiles_lock);

                if (flags & BTRFS_BLOCK_GROUP_DATA)
                        flags |= fs_info->avail_data_alloc_bits;
                else if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                        flags |= fs_info->avail_system_alloc_bits;
                else if (flags & BTRFS_BLOCK_GROUP_METADATA)
                        flags |= fs_info->avail_metadata_alloc_bits;
        } while (read_seqretry(&fs_info->profiles_lock, seq));

        return btrfs_reduce_alloc_profile(fs_info, flags);
}

void btrfs_get_block_group(struct btrfs_block_group *cache)
{
        refcount_inc(&cache->refs);
}

void btrfs_put_block_group(struct btrfs_block_group *cache)
{
        if (refcount_dec_and_test(&cache->refs)) {
                WARN_ON(cache->pinned > 0);
                /*
                 * If there was a failure to cleanup a log tree, very likely due
                 * to an IO failure on a writeback attempt of one or more of its
                 * extent buffers, we could not do proper (and cheap) unaccounting
                 * of their reserved space, so don't warn on reserved > 0 in that
                 * case.
                 */
                if (!(cache->flags & BTRFS_BLOCK_GROUP_METADATA) ||
                    !BTRFS_FS_LOG_CLEANUP_ERROR(cache->fs_info))
                        WARN_ON(cache->reserved > 0);

                /*
                 * A block_group shouldn't be on the discard_list anymore.
                 * Remove the block_group from the discard_list to prevent us
                 * from causing a panic due to NULL pointer dereference.
                 */
                if (WARN_ON(!list_empty(&cache->discard_list)))
                        btrfs_discard_cancel_work(&cache->fs_info->discard_ctl,
                                                  cache);

                /*
                 * If not empty, someone is still holding mutex of
                 * full_stripe_lock, which can only be released by caller.
                 * And it will definitely cause use-after-free when caller
                 * tries to release full stripe lock.
                 *
                 * No better way to resolve, but only to warn.
                 */
                WARN_ON(!RB_EMPTY_ROOT(&cache->full_stripe_locks_root.root));
                kfree(cache->free_space_ctl);
                kfree(cache->physical_map);
                kfree(cache);
        }
}

/*
 * This adds the block group to the fs_info rb tree for the block group cache
 */
static int btrfs_add_block_group_cache(struct btrfs_fs_info *info,
                                       struct btrfs_block_group *block_group)
{
        struct rb_node **p;
        struct rb_node *parent = NULL;
        struct btrfs_block_group *cache;
        bool leftmost = true;

        ASSERT(block_group->length != 0);

        write_lock(&info->block_group_cache_lock);
        p = &info->block_group_cache_tree.rb_root.rb_node;

        while (*p) {
                parent = *p;
                cache = rb_entry(parent, struct btrfs_block_group, cache_node);
                if (block_group->start < cache->start) {
                        p = &(*p)->rb_left;
                } else if (block_group->start > cache->start) {
                        p = &(*p)->rb_right;
                        leftmost = false;
                } else {
                        write_unlock(&info->block_group_cache_lock);
                        return -EEXIST;
                }
        }

        rb_link_node(&block_group->cache_node, parent, p);
        rb_insert_color_cached(&block_group->cache_node,
                               &info->block_group_cache_tree, leftmost);

        write_unlock(&info->block_group_cache_lock);

        return 0;
}

/*
 * This will return the block group at or after bytenr if contains is 0, else
 * it will return the block group that contains the bytenr
 */
static struct btrfs_block_group *block_group_cache_tree_search(
                struct btrfs_fs_info *info, u64 bytenr, int contains)
{
        struct btrfs_block_group *cache, *ret = NULL;
        struct rb_node *n;
        u64 end, start;

        read_lock(&info->block_group_cache_lock);
        n = info->block_group_cache_tree.rb_root.rb_node;

        while (n) {
                cache = rb_entry(n, struct btrfs_block_group, cache_node);
                end = cache->start + cache->length - 1;
                start = cache->start;

                if (bytenr < start) {
                        if (!contains && (!ret || start < ret->start))
                                ret = cache;
                        n = n->rb_left;
                } else if (bytenr > start) {
                        if (contains && bytenr <= end) {
                                ret = cache;
                                break;
                        }
                        n = n->rb_right;
                } else {
                        ret = cache;
                        break;
                }
        }
        if (ret)
                btrfs_get_block_group(ret);
        read_unlock(&info->block_group_cache_lock);

        return ret;
}

/*
 * Return the block group that starts at or after bytenr
 */
struct btrfs_block_group *btrfs_lookup_first_block_group(
                struct btrfs_fs_info *info, u64 bytenr)
{
        return block_group_cache_tree_search(info, bytenr, 0);
}

/*
 * Return the block group that contains the given bytenr
 */
struct btrfs_block_group *btrfs_lookup_block_group(
                struct btrfs_fs_info *info, u64 bytenr)
{
        return block_group_cache_tree_search(info, bytenr, 1);
}

struct btrfs_block_group *btrfs_next_block_group(
                struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct rb_node *node;

        read_lock(&fs_info->block_group_cache_lock);

        /* If our block group was removed, we need a full search. */
        if (RB_EMPTY_NODE(&cache->cache_node)) {
                const u64 next_bytenr = cache->start + cache->length;

                read_unlock(&fs_info->block_group_cache_lock);
                btrfs_put_block_group(cache);
                return btrfs_lookup_first_block_group(fs_info, next_bytenr);
        }
        node = rb_next(&cache->cache_node);
        btrfs_put_block_group(cache);
        if (node) {
                cache = rb_entry(node, struct btrfs_block_group, cache_node);
                btrfs_get_block_group(cache);
        } else
                cache = NULL;
        read_unlock(&fs_info->block_group_cache_lock);
        return cache;
}

/**
 * Check if we can do a NOCOW write for a given extent.
 *
 * @fs_info:       The filesystem information object.
 * @bytenr:        Logical start address of the extent.
 *
 * Check if we can do a NOCOW write for the given extent, and increments the
 * number of NOCOW writers in the block group that contains the extent, as long
 * as the block group exists and it's currently not in read-only mode.
 *
 * Returns: A non-NULL block group pointer if we can do a NOCOW write, the caller
 *          is responsible for calling btrfs_dec_nocow_writers() later.
 *
 *          Or NULL if we can not do a NOCOW write
 */
struct btrfs_block_group *btrfs_inc_nocow_writers(struct btrfs_fs_info *fs_info,
                                                  u64 bytenr)
{
        struct btrfs_block_group *bg;
        bool can_nocow = true;

        bg = btrfs_lookup_block_group(fs_info, bytenr);
        if (!bg)
                return NULL;

        spin_lock(&bg->lock);
        if (bg->ro)
                can_nocow = false;
        else
                atomic_inc(&bg->nocow_writers);
        spin_unlock(&bg->lock);

        if (!can_nocow) {
                btrfs_put_block_group(bg);
                return NULL;
        }

        /* No put on block group, done by btrfs_dec_nocow_writers(). */
        return bg;
}

/**
 * Decrement the number of NOCOW writers in a block group.
 *
 * @bg:       The block group.
 *
 * This is meant to be called after a previous call to btrfs_inc_nocow_writers(),
 * and on the block group returned by that call. Typically this is called after
 * creating an ordered extent for a NOCOW write, to prevent races with scrub and
 * relocation.
 *
 * After this call, the caller should not use the block group anymore. It it wants
 * to use it, then it should get a reference on it before calling this function.
 */
void btrfs_dec_nocow_writers(struct btrfs_block_group *bg)
{
        if (atomic_dec_and_test(&bg->nocow_writers))
                wake_up_var(&bg->nocow_writers);

        /* For the lookup done by a previous call to btrfs_inc_nocow_writers(). */
        btrfs_put_block_group(bg);
}

void btrfs_wait_nocow_writers(struct btrfs_block_group *bg)
{
        wait_var_event(&bg->nocow_writers, !atomic_read(&bg->nocow_writers));
}

void btrfs_dec_block_group_reservations(struct btrfs_fs_info *fs_info,
                                        const u64 start)
{
        struct btrfs_block_group *bg;

        bg = btrfs_lookup_block_group(fs_info, start);
        ASSERT(bg);
        if (atomic_dec_and_test(&bg->reservations))
                wake_up_var(&bg->reservations);
        btrfs_put_block_group(bg);
}

void btrfs_wait_block_group_reservations(struct btrfs_block_group *bg)
{
        struct btrfs_space_info *space_info = bg->space_info;

        ASSERT(bg->ro);

        if (!(bg->flags & BTRFS_BLOCK_GROUP_DATA))
                return;

        /*
         * Our block group is read only but before we set it to read only,
         * some task might have had allocated an extent from it already, but it
         * has not yet created a respective ordered extent (and added it to a
         * root's list of ordered extents).
         * Therefore wait for any task currently allocating extents, since the
         * block group's reservations counter is incremented while a read lock
         * on the groups' semaphore is held and decremented after releasing
         * the read access on that semaphore and creating the ordered extent.
         */
        down_write(&space_info->groups_sem);
        up_write(&space_info->groups_sem);

        wait_var_event(&bg->reservations, !atomic_read(&bg->reservations));
}

struct btrfs_caching_control *btrfs_get_caching_control(
                struct btrfs_block_group *cache)
{
        struct btrfs_caching_control *ctl;

        spin_lock(&cache->lock);
        if (!cache->caching_ctl) {
                spin_unlock(&cache->lock);
                return NULL;
        }

        ctl = cache->caching_ctl;
        refcount_inc(&ctl->count);
        spin_unlock(&cache->lock);
        return ctl;
}

void btrfs_put_caching_control(struct btrfs_caching_control *ctl)
{
        if (refcount_dec_and_test(&ctl->count))
                kfree(ctl);
}

/*
 * When we wait for progress in the block group caching, its because our
 * allocation attempt failed at least once.  So, we must sleep and let some
 * progress happen before we try again.
 *
 * This function will sleep at least once waiting for new free space to show
 * up, and then it will check the block group free space numbers for our min
 * num_bytes.  Another option is to have it go ahead and look in the rbtree for
 * a free extent of a given size, but this is a good start.
 *
 * Callers of this must check if cache->cached == BTRFS_CACHE_ERROR before using
 * any of the information in this block group.
 */
void btrfs_wait_block_group_cache_progress(struct btrfs_block_group *cache,
                                           u64 num_bytes)
{
        struct btrfs_caching_control *caching_ctl;

        caching_ctl = btrfs_get_caching_control(cache);
        if (!caching_ctl)
                return;

        wait_event(caching_ctl->wait, btrfs_block_group_done(cache) ||
                   (cache->free_space_ctl->free_space >= num_bytes));

        btrfs_put_caching_control(caching_ctl);
}

static int btrfs_caching_ctl_wait_done(struct btrfs_block_group *cache,
                                       struct btrfs_caching_control *caching_ctl)
{
        wait_event(caching_ctl->wait, btrfs_block_group_done(cache));
        return cache->cached == BTRFS_CACHE_ERROR ? -EIO : 0;
}

static int btrfs_wait_block_group_cache_done(struct btrfs_block_group *cache)
{
        struct btrfs_caching_control *caching_ctl;
        int ret;

        caching_ctl = btrfs_get_caching_control(cache);
        if (!caching_ctl)
                return (cache->cached == BTRFS_CACHE_ERROR) ? -EIO : 0;
        ret = btrfs_caching_ctl_wait_done(cache, caching_ctl);
        btrfs_put_caching_control(caching_ctl);
        return ret;
}

#ifdef CONFIG_BTRFS_DEBUG
static void fragment_free_space(struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        u64 start = block_group->start;
        u64 len = block_group->length;
        u64 chunk = block_group->flags & BTRFS_BLOCK_GROUP_METADATA ?
                fs_info->nodesize : fs_info->sectorsize;
        u64 step = chunk << 1;

        while (len > chunk) {
                btrfs_remove_free_space(block_group, start, chunk);
                start += step;
                if (len < step)
                        len = 0;
                else
                        len -= step;
        }
}
#endif

/*
 * This is only called by btrfs_cache_block_group, since we could have freed
 * extents we need to check the pinned_extents for any extents that can't be
 * used yet since their free space will be released as soon as the transaction
 * commits.
 */
u64 add_new_free_space(struct btrfs_block_group *block_group, u64 start, u64 end)
{
        struct btrfs_fs_info *info = block_group->fs_info;
        u64 extent_start, extent_end, size, total_added = 0;
        int ret;

        while (start < end) {
                ret = find_first_extent_bit(&info->excluded_extents, start,
                                            &extent_start, &extent_end,
                                            EXTENT_DIRTY | EXTENT_UPTODATE,
                                            NULL);
                if (ret)
                        break;

                if (extent_start <= start) {
                        start = extent_end + 1;
                } else if (extent_start > start && extent_start < end) {
                        size = extent_start - start;
                        total_added += size;
                        ret = btrfs_add_free_space_async_trimmed(block_group,
                                                                 start, size);
                        BUG_ON(ret); /* -ENOMEM or logic error */
                        start = extent_end + 1;
                } else {
                        break;
                }
        }

        if (start < end) {
                size = end - start;
                total_added += size;
                ret = btrfs_add_free_space_async_trimmed(block_group, start,
                                                         size);
                BUG_ON(ret); /* -ENOMEM or logic error */
        }

        return total_added;
}

static int load_extent_tree_free(struct btrfs_caching_control *caching_ctl)
{
        struct btrfs_block_group *block_group = caching_ctl->block_group;
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_root *extent_root;
        struct btrfs_path *path;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        u64 total_found = 0;
        u64 last = 0;
        u32 nritems;
        int ret;
        bool wakeup = true;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        last = max_t(u64, block_group->start, BTRFS_SUPER_INFO_OFFSET);
        extent_root = btrfs_extent_root(fs_info, last);

#ifdef CONFIG_BTRFS_DEBUG
        /*
         * If we're fragmenting we don't want to make anybody think we can
         * allocate from this block group until we've had a chance to fragment
         * the free space.
         */
        if (btrfs_should_fragment_free_space(block_group))
                wakeup = false;
#endif
        /*
         * We don't want to deadlock with somebody trying to allocate a new
         * extent for the extent root while also trying to search the extent
         * root to add free space.  So we skip locking and search the commit
         * root, since its read-only
         */
        path->skip_locking = 1;
        path->search_commit_root = 1;
        path->reada = READA_FORWARD;

        key.objectid = last;
        key.offset = 0;
        key.type = BTRFS_EXTENT_ITEM_KEY;

next:
        ret = btrfs_search_slot(NULL, extent_root, &key, path, 0, 0);
        if (ret < 0)
                goto out;

        leaf = path->nodes[0];
        nritems = btrfs_header_nritems(leaf);

        while (1) {
                if (btrfs_fs_closing(fs_info) > 1) {
                        last = (u64)-1;
                        break;
                }

                if (path->slots[0] < nritems) {
                        btrfs_item_key_to_cpu(leaf, &key, path->slots[0]);
                } else {
                        ret = btrfs_find_next_key(extent_root, path, &key, 0, 0);
                        if (ret)
                                break;

                        if (need_resched() ||
                            rwsem_is_contended(&fs_info->commit_root_sem)) {
                                btrfs_release_path(path);
                                up_read(&fs_info->commit_root_sem);
                                mutex_unlock(&caching_ctl->mutex);
                                cond_resched();
                                mutex_lock(&caching_ctl->mutex);
                                down_read(&fs_info->commit_root_sem);
                                goto next;
                        }

                        ret = btrfs_next_leaf(extent_root, path);
                        if (ret < 0)
                                goto out;
                        if (ret)
                                break;
                        leaf = path->nodes[0];
                        nritems = btrfs_header_nritems(leaf);
                        continue;
                }

                if (key.objectid < last) {
                        key.objectid = last;
                        key.offset = 0;
                        key.type = BTRFS_EXTENT_ITEM_KEY;
                        btrfs_release_path(path);
                        goto next;
                }

                if (key.objectid < block_group->start) {
                        path->slots[0]++;
                        continue;
                }

                if (key.objectid >= block_group->start + block_group->length)
                        break;

                if (key.type == BTRFS_EXTENT_ITEM_KEY ||
                    key.type == BTRFS_METADATA_ITEM_KEY) {
                        total_found += add_new_free_space(block_group, last,
                                                          key.objectid);
                        if (key.type == BTRFS_METADATA_ITEM_KEY)
                                last = key.objectid +
                                        fs_info->nodesize;
                        else
                                last = key.objectid + key.offset;

                        if (total_found > CACHING_CTL_WAKE_UP) {
                                total_found = 0;
                                if (wakeup)
                                        wake_up(&caching_ctl->wait);
                        }
                }
                path->slots[0]++;
        }
        ret = 0;

        total_found += add_new_free_space(block_group, last,
                                block_group->start + block_group->length);

out:
        btrfs_free_path(path);
        return ret;
}

static noinline void caching_thread(struct btrfs_work *work)
{
        struct btrfs_block_group *block_group;
        struct btrfs_fs_info *fs_info;
        struct btrfs_caching_control *caching_ctl;
        int ret;

        caching_ctl = container_of(work, struct btrfs_caching_control, work);
        block_group = caching_ctl->block_group;
        fs_info = block_group->fs_info;

        mutex_lock(&caching_ctl->mutex);
        down_read(&fs_info->commit_root_sem);

        if (btrfs_test_opt(fs_info, SPACE_CACHE)) {
                ret = load_free_space_cache(block_group);
                if (ret == 1) {
                        ret = 0;
                        goto done;
                }

                /*
                 * We failed to load the space cache, set ourselves to
                 * CACHE_STARTED and carry on.
                 */
                spin_lock(&block_group->lock);
                block_group->cached = BTRFS_CACHE_STARTED;
                spin_unlock(&block_group->lock);
                wake_up(&caching_ctl->wait);
        }

        /*
         * If we are in the transaction that populated the free space tree we
         * can't actually cache from the free space tree as our commit root and
         * real root are the same, so we could change the contents of the blocks
         * while caching.  Instead do the slow caching in this case, and after
         * the transaction has committed we will be safe.
         */
        if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE) &&
            !(test_bit(BTRFS_FS_FREE_SPACE_TREE_UNTRUSTED, &fs_info->flags)))
                ret = load_free_space_tree(caching_ctl);
        else
                ret = load_extent_tree_free(caching_ctl);
done:
        spin_lock(&block_group->lock);
        block_group->caching_ctl = NULL;
        block_group->cached = ret ? BTRFS_CACHE_ERROR : BTRFS_CACHE_FINISHED;
        spin_unlock(&block_group->lock);

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(block_group)) {
                u64 bytes_used;

                spin_lock(&block_group->space_info->lock);
                spin_lock(&block_group->lock);
                bytes_used = block_group->length - block_group->used;
                block_group->space_info->bytes_used += bytes_used >> 1;
                spin_unlock(&block_group->lock);
                spin_unlock(&block_group->space_info->lock);
                fragment_free_space(block_group);
        }
#endif

        up_read(&fs_info->commit_root_sem);
        btrfs_free_excluded_extents(block_group);
        mutex_unlock(&caching_ctl->mutex);

        wake_up(&caching_ctl->wait);

        btrfs_put_caching_control(caching_ctl);
        btrfs_put_block_group(block_group);
}

int btrfs_cache_block_group(struct btrfs_block_group *cache, bool wait)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct btrfs_caching_control *caching_ctl = NULL;
        int ret = 0;

        /* Allocator for zoned filesystems does not use the cache at all */
        if (btrfs_is_zoned(fs_info))
                return 0;

        caching_ctl = kzalloc(sizeof(*caching_ctl), GFP_NOFS);
        if (!caching_ctl)
                return -ENOMEM;

        INIT_LIST_HEAD(&caching_ctl->list);
        mutex_init(&caching_ctl->mutex);
        init_waitqueue_head(&caching_ctl->wait);
        caching_ctl->block_group = cache;
        refcount_set(&caching_ctl->count, 2);
        btrfs_init_work(&caching_ctl->work, caching_thread, NULL, NULL);

        spin_lock(&cache->lock);
        if (cache->cached != BTRFS_CACHE_NO) {
                kfree(caching_ctl);

                caching_ctl = cache->caching_ctl;
                if (caching_ctl)
                        refcount_inc(&caching_ctl->count);
                spin_unlock(&cache->lock);
                goto out;
        }
        WARN_ON(cache->caching_ctl);
        cache->caching_ctl = caching_ctl;
        cache->cached = BTRFS_CACHE_STARTED;
        spin_unlock(&cache->lock);

        write_lock(&fs_info->block_group_cache_lock);
        refcount_inc(&caching_ctl->count);
        list_add_tail(&caching_ctl->list, &fs_info->caching_block_groups);
        write_unlock(&fs_info->block_group_cache_lock);

        btrfs_get_block_group(cache);

        btrfs_queue_work(fs_info->caching_workers, &caching_ctl->work);
out:
        if (wait && caching_ctl)
                ret = btrfs_caching_ctl_wait_done(cache, caching_ctl);
        if (caching_ctl)
                btrfs_put_caching_control(caching_ctl);

        return ret;
}

static void clear_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
        u64 extra_flags = chunk_to_extended(flags) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        write_seqlock(&fs_info->profiles_lock);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                fs_info->avail_data_alloc_bits &= ~extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_METADATA)
                fs_info->avail_metadata_alloc_bits &= ~extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                fs_info->avail_system_alloc_bits &= ~extra_flags;
        write_sequnlock(&fs_info->profiles_lock);
}

/*
 * Clear incompat bits for the following feature(s):
 *
 * - RAID56 - in case there's neither RAID5 nor RAID6 profile block group
 *            in the whole filesystem
 *
 * - RAID1C34 - same as above for RAID1C3 and RAID1C4 block groups
 */
static void clear_incompat_bg_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
        bool found_raid56 = false;
        bool found_raid1c34 = false;

        if ((flags & BTRFS_BLOCK_GROUP_RAID56_MASK) ||
            (flags & BTRFS_BLOCK_GROUP_RAID1C3) ||
            (flags & BTRFS_BLOCK_GROUP_RAID1C4)) {
                struct list_head *head = &fs_info->space_info;
                struct btrfs_space_info *sinfo;

                list_for_each_entry_rcu(sinfo, head, list) {
                        down_read(&sinfo->groups_sem);
                        if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID5]))
                                found_raid56 = true;
                        if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID6]))
                                found_raid56 = true;
                        if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID1C3]))
                                found_raid1c34 = true;
                        if (!list_empty(&sinfo->block_groups[BTRFS_RAID_RAID1C4]))
                                found_raid1c34 = true;
                        up_read(&sinfo->groups_sem);
                }
                if (!found_raid56)
                        btrfs_clear_fs_incompat(fs_info, RAID56);
                if (!found_raid1c34)
                        btrfs_clear_fs_incompat(fs_info, RAID1C34);
        }
}

static int remove_block_group_item(struct btrfs_trans_handle *trans,
                                   struct btrfs_path *path,
                                   struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_root *root;
        struct btrfs_key key;
        int ret;

        root = btrfs_block_group_root(fs_info);
        key.objectid = block_group->start;
        key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
        key.offset = block_group->length;

        ret = btrfs_search_slot(trans, root, &key, path, -1, 1);
        if (ret > 0)
                ret = -ENOENT;
        if (ret < 0)
                return ret;

        ret = btrfs_del_item(trans, root, path);
        return ret;
}

int btrfs_remove_block_group(struct btrfs_trans_handle *trans,
                             u64 group_start, struct extent_map *em)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_path *path;
        struct btrfs_block_group *block_group;
        struct btrfs_free_cluster *cluster;
        struct inode *inode;
        struct kobject *kobj = NULL;
        int ret;
        int index;
        int factor;
        struct btrfs_caching_control *caching_ctl = NULL;
        bool remove_em;
        bool remove_rsv = false;

        block_group = btrfs_lookup_block_group(fs_info, group_start);
        BUG_ON(!block_group);
        BUG_ON(!block_group->ro);

        trace_btrfs_remove_block_group(block_group);
        /*
         * Free the reserved super bytes from this block group before
         * remove it.
         */
        btrfs_free_excluded_extents(block_group);
        btrfs_free_ref_tree_range(fs_info, block_group->start,
                                  block_group->length);

        index = btrfs_bg_flags_to_raid_index(block_group->flags);
        factor = btrfs_bg_type_to_factor(block_group->flags);

        /* make sure this block group isn't part of an allocation cluster */
        cluster = &fs_info->data_alloc_cluster;
        spin_lock(&cluster->refill_lock);
        btrfs_return_cluster_to_free_space(block_group, cluster);
        spin_unlock(&cluster->refill_lock);

        /*
         * make sure this block group isn't part of a metadata
         * allocation cluster
         */
        cluster = &fs_info->meta_alloc_cluster;
        spin_lock(&cluster->refill_lock);
        btrfs_return_cluster_to_free_space(block_group, cluster);
        spin_unlock(&cluster->refill_lock);

        btrfs_clear_treelog_bg(block_group);
        btrfs_clear_data_reloc_bg(block_group);

        path = btrfs_alloc_path();
        if (!path) {
                ret = -ENOMEM;
                goto out;
        }

        /*
         * get the inode first so any iput calls done for the io_list
         * aren't the final iput (no unlinks allowed now)
         */
        inode = lookup_free_space_inode(block_group, path);

        mutex_lock(&trans->transaction->cache_write_mutex);
        /*
         * Make sure our free space cache IO is done before removing the
         * free space inode
         */
        spin_lock(&trans->transaction->dirty_bgs_lock);
        if (!list_empty(&block_group->io_list)) {
                list_del_init(&block_group->io_list);

                WARN_ON(!IS_ERR(inode) && inode != block_group->io_ctl.inode);

                spin_unlock(&trans->transaction->dirty_bgs_lock);
                btrfs_wait_cache_io(trans, block_group, path);
                btrfs_put_block_group(block_group);
                spin_lock(&trans->transaction->dirty_bgs_lock);
        }

        if (!list_empty(&block_group->dirty_list)) {
                list_del_init(&block_group->dirty_list);
                remove_rsv = true;
                btrfs_put_block_group(block_group);
        }
        spin_unlock(&trans->transaction->dirty_bgs_lock);
        mutex_unlock(&trans->transaction->cache_write_mutex);

        ret = btrfs_remove_free_space_inode(trans, inode, block_group);
        if (ret)
                goto out;

        write_lock(&fs_info->block_group_cache_lock);
        rb_erase_cached(&block_group->cache_node,
                        &fs_info->block_group_cache_tree);
        RB_CLEAR_NODE(&block_group->cache_node);

        /* Once for the block groups rbtree */
        btrfs_put_block_group(block_group);

        write_unlock(&fs_info->block_group_cache_lock);

        down_write(&block_group->space_info->groups_sem);
        /*
         * we must use list_del_init so people can check to see if they
         * are still on the list after taking the semaphore
         */
        list_del_init(&block_group->list);
        if (list_empty(&block_group->space_info->block_groups[index])) {
                kobj = block_group->space_info->block_group_kobjs[index];
                block_group->space_info->block_group_kobjs[index] = NULL;
                clear_avail_alloc_bits(fs_info, block_group->flags);
        }
        up_write(&block_group->space_info->groups_sem);
        clear_incompat_bg_bits(fs_info, block_group->flags);
        if (kobj) {
                kobject_del(kobj);
                kobject_put(kobj);
        }

        if (block_group->cached == BTRFS_CACHE_STARTED)
                btrfs_wait_block_group_cache_done(block_group);

        write_lock(&fs_info->block_group_cache_lock);
        caching_ctl = btrfs_get_caching_control(block_group);
        if (!caching_ctl) {
                struct btrfs_caching_control *ctl;

                list_for_each_entry(ctl, &fs_info->caching_block_groups, list) {
                        if (ctl->block_group == block_group) {
                                caching_ctl = ctl;
                                refcount_inc(&caching_ctl->count);
                                break;
                        }
                }
        }
        if (caching_ctl)
                list_del_init(&caching_ctl->list);
        write_unlock(&fs_info->block_group_cache_lock);

        if (caching_ctl) {
                /* Once for the caching bgs list and once for us. */
                btrfs_put_caching_control(caching_ctl);
                btrfs_put_caching_control(caching_ctl);
        }

        spin_lock(&trans->transaction->dirty_bgs_lock);
        WARN_ON(!list_empty(&block_group->dirty_list));
        WARN_ON(!list_empty(&block_group->io_list));
        spin_unlock(&trans->transaction->dirty_bgs_lock);

        btrfs_remove_free_space_cache(block_group);

        spin_lock(&block_group->space_info->lock);
        list_del_init(&block_group->ro_list);

        if (btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
                WARN_ON(block_group->space_info->total_bytes
                        < block_group->length);
                WARN_ON(block_group->space_info->bytes_readonly
                        < block_group->length - block_group->zone_unusable);
                WARN_ON(block_group->space_info->bytes_zone_unusable
                        < block_group->zone_unusable);
                WARN_ON(block_group->space_info->disk_total
                        < block_group->length * factor);
                WARN_ON(test_bit(BLOCK_GROUP_FLAG_ZONE_IS_ACTIVE,
                                 &block_group->runtime_flags) &&
                        block_group->space_info->active_total_bytes
                        < block_group->length);
        }
        block_group->space_info->total_bytes -= block_group->length;
        if (test_bit(BLOCK_GROUP_FLAG_ZONE_IS_ACTIVE, &block_group->runtime_flags))
                block_group->space_info->active_total_bytes -= block_group->length;
        block_group->space_info->bytes_readonly -=
                (block_group->length - block_group->zone_unusable);
        block_group->space_info->bytes_zone_unusable -=
                block_group->zone_unusable;
        block_group->space_info->disk_total -= block_group->length * factor;

        spin_unlock(&block_group->space_info->lock);

        /*
         * Remove the free space for the block group from the free space tree
         * and the block group's item from the extent tree before marking the
         * block group as removed. This is to prevent races with tasks that
         * freeze and unfreeze a block group, this task and another task
         * allocating a new block group - the unfreeze task ends up removing
         * the block group's extent map before the task calling this function
         * deletes the block group item from the extent tree, allowing for
         * another task to attempt to create another block group with the same
         * item key (and failing with -EEXIST and a transaction abort).
         */
        ret = remove_block_group_free_space(trans, block_group);
        if (ret)
                goto out;

        ret = remove_block_group_item(trans, path, block_group);
        if (ret < 0)
                goto out;

        spin_lock(&block_group->lock);
        set_bit(BLOCK_GROUP_FLAG_REMOVED, &block_group->runtime_flags);

        /*
         * At this point trimming or scrub can't start on this block group,
         * because we removed the block group from the rbtree
         * fs_info->block_group_cache_tree so no one can't find it anymore and
         * even if someone already got this block group before we removed it
         * from the rbtree, they have already incremented block_group->frozen -
         * if they didn't, for the trimming case they won't find any free space
         * entries because we already removed them all when we called
         * btrfs_remove_free_space_cache().
         *
         * And we must not remove the extent map from the fs_info->mapping_tree
         * to prevent the same logical address range and physical device space
         * ranges from being reused for a new block group. This is needed to
         * avoid races with trimming and scrub.
         *
         * An fs trim operation (btrfs_trim_fs() / btrfs_ioctl_fitrim()) is
         * completely transactionless, so while it is trimming a range the
         * currently running transaction might finish and a new one start,
         * allowing for new block groups to be created that can reuse the same
         * physical device locations unless we take this special care.
         *
         * There may also be an implicit trim operation if the file system
         * is mounted with -odiscard. The same protections must remain
         * in place until the extents have been discarded completely when
         * the transaction commit has completed.
         */
        remove_em = (atomic_read(&block_group->frozen) == 0);
        spin_unlock(&block_group->lock);

        if (remove_em) {
                struct extent_map_tree *em_tree;

                em_tree = &fs_info->mapping_tree;
                write_lock(&em_tree->lock);
                remove_extent_mapping(em_tree, em);
                write_unlock(&em_tree->lock);
                /* once for the tree */
                free_extent_map(em);
        }

out:
        /* Once for the lookup reference */
        btrfs_put_block_group(block_group);
        if (remove_rsv)
                btrfs_delayed_refs_rsv_release(fs_info, 1);
        btrfs_free_path(path);
        return ret;
}

struct btrfs_trans_handle *btrfs_start_trans_remove_block_group(
                struct btrfs_fs_info *fs_info, const u64 chunk_offset)
{
        struct btrfs_root *root = btrfs_block_group_root(fs_info);
        struct extent_map_tree *em_tree = &fs_info->mapping_tree;
        struct extent_map *em;
        struct map_lookup *map;
        unsigned int num_items;

        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, chunk_offset, 1);
        read_unlock(&em_tree->lock);
        ASSERT(em && em->start == chunk_offset);

        /*
         * We need to reserve 3 + N units from the metadata space info in order
         * to remove a block group (done at btrfs_remove_chunk() and at
         * btrfs_remove_block_group()), which are used for:
         *
         * 1 unit for adding the free space inode's orphan (located in the tree
         * of tree roots).
         * 1 unit for deleting the block group item (located in the extent
         * tree).
         * 1 unit for deleting the free space item (located in tree of tree
         * roots).
         * N units for deleting N device extent items corresponding to each
         * stripe (located in the device tree).
         *
         * In order to remove a block group we also need to reserve units in the
         * system space info in order to update the chunk tree (update one or
         * more device items and remove one chunk item), but this is done at
         * btrfs_remove_chunk() through a call to check_system_chunk().
         */
        map = em->map_lookup;
        num_items = 3 + map->num_stripes;
        free_extent_map(em);

        return btrfs_start_transaction_fallback_global_rsv(root, num_items);
}

/*
 * Mark block group @cache read-only, so later write won't happen to block
 * group @cache.
 *
 * If @force is not set, this function will only mark the block group readonly
 * if we have enough free space (1M) in other metadata/system block groups.
 * If @force is not set, this function will mark the block group readonly
 * without checking free space.
 *
 * NOTE: This function doesn't care if other block groups can contain all the
 * data in this block group. That check should be done by relocation routine,
 * not this function.
 */
static int inc_block_group_ro(struct btrfs_block_group *cache, int force)
{
        struct btrfs_space_info *sinfo = cache->space_info;
        u64 num_bytes;
        int ret = -ENOSPC;

        spin_lock(&sinfo->lock);
        spin_lock(&cache->lock);

        if (cache->swap_extents) {
                ret = -ETXTBSY;
                goto out;
        }

        if (cache->ro) {
                cache->ro++;
                ret = 0;
                goto out;
        }

        num_bytes = cache->length - cache->reserved - cache->pinned -
                    cache->bytes_super - cache->zone_unusable - cache->used;

        /*
         * Data never overcommits, even in mixed mode, so do just the straight
         * check of left over space in how much we have allocated.
         */
        if (force) {
                ret = 0;
        } else if (sinfo->flags & BTRFS_BLOCK_GROUP_DATA) {
                u64 sinfo_used = btrfs_space_info_used(sinfo, true);

                /*
                 * Here we make sure if we mark this bg RO, we still have enough
                 * free space as buffer.
                 */
                if (sinfo_used + num_bytes <= sinfo->total_bytes)
                        ret = 0;
        } else {
                /*
                 * We overcommit metadata, so we need to do the
                 * btrfs_can_overcommit check here, and we need to pass in
                 * BTRFS_RESERVE_NO_FLUSH to give ourselves the most amount of
                 * leeway to allow us to mark this block group as read only.
                 */
                if (btrfs_can_overcommit(cache->fs_info, sinfo, num_bytes,
                                         BTRFS_RESERVE_NO_FLUSH))
                        ret = 0;
        }

        if (!ret) {
                sinfo->bytes_readonly += num_bytes;
                if (btrfs_is_zoned(cache->fs_info)) {
                        /* Migrate zone_unusable bytes to readonly */
                        sinfo->bytes_readonly += cache->zone_unusable;
                        sinfo->bytes_zone_unusable -= cache->zone_unusable;
                        cache->zone_unusable = 0;
                }
                cache->ro++;
                list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
        }
out:
        spin_unlock(&cache->lock);
        spin_unlock(&sinfo->lock);
        if (ret == -ENOSPC && btrfs_test_opt(cache->fs_info, ENOSPC_DEBUG)) {
                btrfs_info(cache->fs_info,
                        "unable to make block group %llu ro", cache->start);
                btrfs_dump_space_info(cache->fs_info, cache->space_info, 0, 0);
        }
        return ret;
}

static bool clean_pinned_extents(struct btrfs_trans_handle *trans,
                                 struct btrfs_block_group *bg)
{
        struct btrfs_fs_info *fs_info = bg->fs_info;
        struct btrfs_transaction *prev_trans = NULL;
        const u64 start = bg->start;
        const u64 end = start + bg->length - 1;
        int ret;

        spin_lock(&fs_info->trans_lock);
        if (trans->transaction->list.prev != &fs_info->trans_list) {
                prev_trans = list_last_entry(&trans->transaction->list,
                                             struct btrfs_transaction, list);
                refcount_inc(&prev_trans->use_count);
        }
        spin_unlock(&fs_info->trans_lock);

        /*
         * Hold the unused_bg_unpin_mutex lock to avoid racing with
         * btrfs_finish_extent_commit(). If we are at transaction N, another
         * task might be running finish_extent_commit() for the previous
         * transaction N - 1, and have seen a range belonging to the block
         * group in pinned_extents before we were able to clear the whole block
         * group range from pinned_extents. This means that task can lookup for
         * the block group after we unpinned it from pinned_extents and removed
         * it, leading to a BUG_ON() at unpin_extent_range().
         */
        mutex_lock(&fs_info->unused_bg_unpin_mutex);
        if (prev_trans) {
                ret = clear_extent_bits(&prev_trans->pinned_extents, start, end,
                                        EXTENT_DIRTY);
                if (ret)
                        goto out;
        }

        ret = clear_extent_bits(&trans->transaction->pinned_extents, start, end,
                                EXTENT_DIRTY);
out:
        mutex_unlock(&fs_info->unused_bg_unpin_mutex);
        if (prev_trans)
                btrfs_put_transaction(prev_trans);

        return ret == 0;
}

/*
 * Process the unused_bgs list and remove any that don't have any allocated
 * space inside of them.
 */
void btrfs_delete_unused_bgs(struct btrfs_fs_info *fs_info)
{
        struct btrfs_block_group *block_group;
        struct btrfs_space_info *space_info;
        struct btrfs_trans_handle *trans;
        const bool async_trim_enabled = btrfs_test_opt(fs_info, DISCARD_ASYNC);
        int ret = 0;

        if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
                return;

        if (btrfs_fs_closing(fs_info))
                return;

        /*
         * Long running balances can keep us blocked here for eternity, so
         * simply skip deletion if we're unable to get the mutex.
         */
        if (!mutex_trylock(&fs_info->reclaim_bgs_lock))
                return;

        spin_lock(&fs_info->unused_bgs_lock);
        while (!list_empty(&fs_info->unused_bgs)) {
                int trimming;

                block_group = list_first_entry(&fs_info->unused_bgs,
                                               struct btrfs_block_group,
                                               bg_list);
                list_del_init(&block_group->bg_list);

                space_info = block_group->space_info;

                if (ret || btrfs_mixed_space_info(space_info)) {
                        btrfs_put_block_group(block_group);
                        continue;
                }
                spin_unlock(&fs_info->unused_bgs_lock);

                btrfs_discard_cancel_work(&fs_info->discard_ctl, block_group);

                /* Don't want to race with allocators so take the groups_sem */
                down_write(&space_info->groups_sem);

                /*
                 * Async discard moves the final block group discard to be prior
                 * to the unused_bgs code path.  Therefore, if it's not fully
                 * trimmed, punt it back to the async discard lists.
                 */
                if (btrfs_test_opt(fs_info, DISCARD_ASYNC) &&
                    !btrfs_is_free_space_trimmed(block_group)) {
                        trace_btrfs_skip_unused_block_group(block_group);
                        up_write(&space_info->groups_sem);
                        /* Requeue if we failed because of async discard */
                        btrfs_discard_queue_work(&fs_info->discard_ctl,
                                                 block_group);
                        goto next;
                }

                spin_lock(&block_group->lock);
                if (block_group->reserved || block_group->pinned ||
                    block_group->used || block_group->ro ||
                    list_is_singular(&block_group->list)) {
                        /*
                         * We want to bail if we made new allocations or have
                         * outstanding allocations in this block group.  We do
                         * the ro check in case balance is currently acting on
                         * this block group.
                         */
                        trace_btrfs_skip_unused_block_group(block_group);
                        spin_unlock(&block_group->lock);
                        up_write(&space_info->groups_sem);
                        goto next;
                }
                spin_unlock(&block_group->lock);

                /* We don't want to force the issue, only flip if it's ok. */
                ret = inc_block_group_ro(block_group, 0);
                up_write(&space_info->groups_sem);
                if (ret < 0) {
                        ret = 0;
                        goto next;
                }

                ret = btrfs_zone_finish(block_group);
                if (ret < 0) {
                        btrfs_dec_block_group_ro(block_group);
                        if (ret == -EAGAIN)
                                ret = 0;
                        goto next;
                }

                /*
                 * Want to do this before we do anything else so we can recover
                 * properly if we fail to join the transaction.
                 */
                trans = btrfs_start_trans_remove_block_group(fs_info,
                                                     block_group->start);
                if (IS_ERR(trans)) {
                        btrfs_dec_block_group_ro(block_group);
                        ret = PTR_ERR(trans);
                        goto next;
                }

                /*
                 * We could have pending pinned extents for this block group,
                 * just delete them, we don't care about them anymore.
                 */
                if (!clean_pinned_extents(trans, block_group)) {
                        btrfs_dec_block_group_ro(block_group);
                        goto end_trans;
                }

                /*
                 * At this point, the block_group is read only and should fail
                 * new allocations.  However, btrfs_finish_extent_commit() can
                 * cause this block_group to be placed back on the discard
                 * lists because now the block_group isn't fully discarded.
                 * Bail here and try again later after discarding everything.
                 */
                spin_lock(&fs_info->discard_ctl.lock);
                if (!list_empty(&block_group->discard_list)) {
                        spin_unlock(&fs_info->discard_ctl.lock);
                        btrfs_dec_block_group_ro(block_group);
                        btrfs_discard_queue_work(&fs_info->discard_ctl,
                                                 block_group);
                        goto end_trans;
                }
                spin_unlock(&fs_info->discard_ctl.lock);

                /* Reset pinned so btrfs_put_block_group doesn't complain */
                spin_lock(&space_info->lock);
                spin_lock(&block_group->lock);

                btrfs_space_info_update_bytes_pinned(fs_info, space_info,
                                                     -block_group->pinned);
                space_info->bytes_readonly += block_group->pinned;
                block_group->pinned = 0;

                spin_unlock(&block_group->lock);
                spin_unlock(&space_info->lock);

                /*
                 * The normal path here is an unused block group is passed here,
                 * then trimming is handled in the transaction commit path.
                 * Async discard interposes before this to do the trimming
                 * before coming down the unused block group path as trimming
                 * will no longer be done later in the transaction commit path.
                 */
                if (!async_trim_enabled && btrfs_test_opt(fs_info, DISCARD_ASYNC))
                        goto flip_async;

                /*
                 * DISCARD can flip during remount. On zoned filesystems, we
                 * need to reset sequential-required zones.
                 */
                trimming = btrfs_test_opt(fs_info, DISCARD_SYNC) ||
                                btrfs_is_zoned(fs_info);

                /* Implicit trim during transaction commit. */
                if (trimming)
                        btrfs_freeze_block_group(block_group);

                /*
                 * Btrfs_remove_chunk will abort the transaction if things go
                 * horribly wrong.
                 */
                ret = btrfs_remove_chunk(trans, block_group->start);

                if (ret) {
                        if (trimming)
                                btrfs_unfreeze_block_group(block_group);
                        goto end_trans;
                }

                /*
                 * If we're not mounted with -odiscard, we can just forget
                 * about this block group. Otherwise we'll need to wait
                 * until transaction commit to do the actual discard.
                 */
                if (trimming) {
                        spin_lock(&fs_info->unused_bgs_lock);
                        /*
                         * A concurrent scrub might have added us to the list
                         * fs_info->unused_bgs, so use a list_move operation
                         * to add the block group to the deleted_bgs list.
                         */
                        list_move(&block_group->bg_list,
                                  &trans->transaction->deleted_bgs);
                        spin_unlock(&fs_info->unused_bgs_lock);
                        btrfs_get_block_group(block_group);
                }
end_trans:
                btrfs_end_transaction(trans);
next:
                btrfs_put_block_group(block_group);
                spin_lock(&fs_info->unused_bgs_lock);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
        mutex_unlock(&fs_info->reclaim_bgs_lock);
        return;

flip_async:
        btrfs_end_transaction(trans);
        mutex_unlock(&fs_info->reclaim_bgs_lock);
        btrfs_put_block_group(block_group);
        btrfs_discard_punt_unused_bgs_list(fs_info);
}

void btrfs_mark_bg_unused(struct btrfs_block_group *bg)
{
        struct btrfs_fs_info *fs_info = bg->fs_info;

        spin_lock(&fs_info->unused_bgs_lock);
        if (list_empty(&bg->bg_list)) {
                btrfs_get_block_group(bg);
                trace_btrfs_add_unused_block_group(bg);
                list_add_tail(&bg->bg_list, &fs_info->unused_bgs);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
}

/*
 * We want block groups with a low number of used bytes to be in the beginning
 * of the list, so they will get reclaimed first.
 */
static int reclaim_bgs_cmp(void *unused, const struct list_head *a,
                           const struct list_head *b)
{
        const struct btrfs_block_group *bg1, *bg2;

        bg1 = list_entry(a, struct btrfs_block_group, bg_list);
        bg2 = list_entry(b, struct btrfs_block_group, bg_list);

        return bg1->used > bg2->used;
}

static inline bool btrfs_should_reclaim(struct btrfs_fs_info *fs_info)
{
        if (btrfs_is_zoned(fs_info))
                return btrfs_zoned_should_reclaim(fs_info);
        return true;
}

static bool should_reclaim_block_group(struct btrfs_block_group *bg, u64 bytes_freed)
{
        const struct btrfs_space_info *space_info = bg->space_info;
        const int reclaim_thresh = READ_ONCE(space_info->bg_reclaim_threshold);
        const u64 new_val = bg->used;
        const u64 old_val = new_val + bytes_freed;
        u64 thresh;

        if (reclaim_thresh == 0)
                return false;

        thresh = div_factor_fine(bg->length, reclaim_thresh);

        /*
         * If we were below the threshold before don't reclaim, we are likely a
         * brand new block group and we don't want to relocate new block groups.
         */
        if (old_val < thresh)
                return false;
        if (new_val >= thresh)
                return false;
        return true;
}

void btrfs_reclaim_bgs_work(struct work_struct *work)
{
        struct btrfs_fs_info *fs_info =
                container_of(work, struct btrfs_fs_info, reclaim_bgs_work);
        struct btrfs_block_group *bg;
        struct btrfs_space_info *space_info;

        if (!test_bit(BTRFS_FS_OPEN, &fs_info->flags))
                return;

        if (btrfs_fs_closing(fs_info))
                return;

        if (!btrfs_should_reclaim(fs_info))
                return;

        sb_start_write(fs_info->sb);

        if (!btrfs_exclop_start(fs_info, BTRFS_EXCLOP_BALANCE)) {
                sb_end_write(fs_info->sb);
                return;
        }

        /*
         * Long running balances can keep us blocked here for eternity, so
         * simply skip reclaim if we're unable to get the mutex.
         */
        if (!mutex_trylock(&fs_info->reclaim_bgs_lock)) {
                btrfs_exclop_finish(fs_info);
                sb_end_write(fs_info->sb);
                return;
        }

        spin_lock(&fs_info->unused_bgs_lock);
        /*
         * Sort happens under lock because we can't simply splice it and sort.
         * The block groups might still be in use and reachable via bg_list,
         * and their presence in the reclaim_bgs list must be preserved.
         */
        list_sort(NULL, &fs_info->reclaim_bgs, reclaim_bgs_cmp);
        while (!list_empty(&fs_info->reclaim_bgs)) {
                u64 zone_unusable;
                int ret = 0;

                bg = list_first_entry(&fs_info->reclaim_bgs,
                                      struct btrfs_block_group,
                                      bg_list);
                list_del_init(&bg->bg_list);

                space_info = bg->space_info;
                spin_unlock(&fs_info->unused_bgs_lock);

                /* Don't race with allocators so take the groups_sem */
                down_write(&space_info->groups_sem);

                spin_lock(&bg->lock);
                if (bg->reserved || bg->pinned || bg->ro) {
                        /*
                         * We want to bail if we made new allocations or have
                         * outstanding allocations in this block group.  We do
                         * the ro check in case balance is currently acting on
                         * this block group.
                         */
                        spin_unlock(&bg->lock);
                        up_write(&space_info->groups_sem);
                        goto next;
                }
                if (bg->used == 0) {
                        /*
                         * It is possible that we trigger relocation on a block
                         * group as its extents are deleted and it first goes
                         * below the threshold, then shortly after goes empty.
                         *
                         * In this case, relocating it does delete it, but has
                         * some overhead in relocation specific metadata, looking
                         * for the non-existent extents and running some extra
                         * transactions, which we can avoid by using one of the
                         * other mechanisms for dealing with empty block groups.
                         */
                        if (!btrfs_test_opt(fs_info, DISCARD_ASYNC))
                                btrfs_mark_bg_unused(bg);
                        spin_unlock(&bg->lock);
                        up_write(&space_info->groups_sem);
                        goto next;

                }
                /*
                 * The block group might no longer meet the reclaim condition by
                 * the time we get around to reclaiming it, so to avoid
                 * reclaiming overly full block_groups, skip reclaiming them.
                 *
                 * Since the decision making process also depends on the amount
                 * being freed, pass in a fake giant value to skip that extra
                 * check, which is more meaningful when adding to the list in
                 * the first place.
                 */
                if (!should_reclaim_block_group(bg, bg->length)) {
                        spin_unlock(&bg->lock);
                        up_write(&space_info->groups_sem);
                        goto next;
                }
                spin_unlock(&bg->lock);

                /* Get out fast, in case we're unmounting the filesystem */
                if (btrfs_fs_closing(fs_info)) {
                        up_write(&space_info->groups_sem);
                        goto next;
                }

                /*
                 * Cache the zone_unusable value before turning the block group
                 * to read only. As soon as the blog group is read only it's
                 * zone_unusable value gets moved to the block group's read-only
                 * bytes and isn't available for calculations anymore.
                 */
                zone_unusable = bg->zone_unusable;
                ret = inc_block_group_ro(bg, 0);
                up_write(&space_info->groups_sem);
                if (ret < 0)
                        goto next;

                btrfs_info(fs_info,
                        "reclaiming chunk %llu with %llu%% used %llu%% unusable",
                                bg->start, div_u64(bg->used * 100, bg->length),
                                div64_u64(zone_unusable * 100, bg->length));
                trace_btrfs_reclaim_block_group(bg);
                ret = btrfs_relocate_chunk(fs_info, bg->start);
                if (ret) {
                        btrfs_dec_block_group_ro(bg);
                        btrfs_err(fs_info, "error relocating chunk %llu",
                                  bg->start);
                }

next:
                btrfs_put_block_group(bg);
                spin_lock(&fs_info->unused_bgs_lock);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
        mutex_unlock(&fs_info->reclaim_bgs_lock);
        btrfs_exclop_finish(fs_info);
        sb_end_write(fs_info->sb);
}

void btrfs_reclaim_bgs(struct btrfs_fs_info *fs_info)
{
        spin_lock(&fs_info->unused_bgs_lock);
        if (!list_empty(&fs_info->reclaim_bgs))
                queue_work(system_unbound_wq, &fs_info->reclaim_bgs_work);
        spin_unlock(&fs_info->unused_bgs_lock);
}

void btrfs_mark_bg_to_reclaim(struct btrfs_block_group *bg)
{
        struct btrfs_fs_info *fs_info = bg->fs_info;

        spin_lock(&fs_info->unused_bgs_lock);
        if (list_empty(&bg->bg_list)) {
                btrfs_get_block_group(bg);
                trace_btrfs_add_reclaim_block_group(bg);
                list_add_tail(&bg->bg_list, &fs_info->reclaim_bgs);
        }
        spin_unlock(&fs_info->unused_bgs_lock);
}

static int read_bg_from_eb(struct btrfs_fs_info *fs_info, struct btrfs_key *key,
                           struct btrfs_path *path)
{
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        struct btrfs_block_group_item bg;
        struct extent_buffer *leaf;
        int slot;
        u64 flags;
        int ret = 0;

        slot = path->slots[0];
        leaf = path->nodes[0];

        em_tree = &fs_info->mapping_tree;
        read_lock(&em_tree->lock);
        em = lookup_extent_mapping(em_tree, key->objectid, key->offset);
        read_unlock(&em_tree->lock);
        if (!em) {
                btrfs_err(fs_info,
                          "logical %llu len %llu found bg but no related chunk",
                          key->objectid, key->offset);
                return -ENOENT;
        }

        if (em->start != key->objectid || em->len != key->offset) {
                btrfs_err(fs_info,
                        "block group %llu len %llu mismatch with chunk %llu len %llu",
                        key->objectid, key->offset, em->start, em->len);
                ret = -EUCLEAN;
                goto out_free_em;
        }

        read_extent_buffer(leaf, &bg, btrfs_item_ptr_offset(leaf, slot),
                           sizeof(bg));
        flags = btrfs_stack_block_group_flags(&bg) &
                BTRFS_BLOCK_GROUP_TYPE_MASK;

        if (flags != (em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
                btrfs_err(fs_info,
"block group %llu len %llu type flags 0x%llx mismatch with chunk type flags 0x%llx",
                          key->objectid, key->offset, flags,
                          (BTRFS_BLOCK_GROUP_TYPE_MASK & em->map_lookup->type));
                ret = -EUCLEAN;
        }

out_free_em:
        free_extent_map(em);
        return ret;
}

static int find_first_block_group(struct btrfs_fs_info *fs_info,
                                  struct btrfs_path *path,
                                  struct btrfs_key *key)
{
        struct btrfs_root *root = btrfs_block_group_root(fs_info);
        int ret;
        struct btrfs_key found_key;

        btrfs_for_each_slot(root, key, &found_key, path, ret) {
                if (found_key.objectid >= key->objectid &&
                    found_key.type == BTRFS_BLOCK_GROUP_ITEM_KEY) {
                        return read_bg_from_eb(fs_info, &found_key, path);
                }
        }
        return ret;
}

static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
{
        u64 extra_flags = chunk_to_extended(flags) &
                                BTRFS_EXTENDED_PROFILE_MASK;

        write_seqlock(&fs_info->profiles_lock);
        if (flags & BTRFS_BLOCK_GROUP_DATA)
                fs_info->avail_data_alloc_bits |= extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_METADATA)
                fs_info->avail_metadata_alloc_bits |= extra_flags;
        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                fs_info->avail_system_alloc_bits |= extra_flags;
        write_sequnlock(&fs_info->profiles_lock);
}

/**
 * Map a physical disk address to a list of logical addresses
 *
 * @fs_info:       the filesystem
 * @chunk_start:   logical address of block group
 * @bdev:          physical device to resolve, can be NULL to indicate any device
 * @physical:      physical address to map to logical addresses
 * @logical:       return array of logical addresses which map to @physical
 * @naddrs:        length of @logical
 * @stripe_len:    size of IO stripe for the given block group
 *
 * Maps a particular @physical disk address to a list of @logical addresses.
 * Used primarily to exclude those portions of a block group that contain super
 * block copies.
 */
int btrfs_rmap_block(struct btrfs_fs_info *fs_info, u64 chunk_start,
                     struct block_device *bdev, u64 physical, u64 **logical,
                     int *naddrs, int *stripe_len)
{
        struct extent_map *em;
        struct map_lookup *map;
        u64 *buf;
        u64 bytenr;
        u64 data_stripe_length;
        u64 io_stripe_size;
        int i, nr = 0;
        int ret = 0;

        em = btrfs_get_chunk_map(fs_info, chunk_start, 1);
        if (IS_ERR(em))
                return -EIO;

        map = em->map_lookup;
        data_stripe_length = em->orig_block_len;
        io_stripe_size = map->stripe_len;
        chunk_start = em->start;

        /* For RAID5/6 adjust to a full IO stripe length */
        if (map->type & BTRFS_BLOCK_GROUP_RAID56_MASK)
                io_stripe_size = map->stripe_len * nr_data_stripes(map);

        buf = kcalloc(map->num_stripes, sizeof(u64), GFP_NOFS);
        if (!buf) {
                ret = -ENOMEM;
                goto out;
        }

        for (i = 0; i < map->num_stripes; i++) {
                bool already_inserted = false;
                u64 stripe_nr;
                u64 offset;
                int j;

                if (!in_range(physical, map->stripes[i].physical,
                              data_stripe_length))
                        continue;

                if (bdev && map->stripes[i].dev->bdev != bdev)
                        continue;

                stripe_nr = physical - map->stripes[i].physical;
                stripe_nr = div64_u64_rem(stripe_nr, map->stripe_len, &offset);

                if (map->type & (BTRFS_BLOCK_GROUP_RAID0 |
                                 BTRFS_BLOCK_GROUP_RAID10)) {
                        stripe_nr = stripe_nr * map->num_stripes + i;
                        stripe_nr = div_u64(stripe_nr, map->sub_stripes);
                }
                /*
                 * The remaining case would be for RAID56, multiply by
                 * nr_data_stripes().  Alternatively, just use rmap_len below
                 * instead of map->stripe_len
                 */

                bytenr = chunk_start + stripe_nr * io_stripe_size + offset;

                /* Ensure we don't add duplicate addresses */
                for (j = 0; j < nr; j++) {
                        if (buf[j] == bytenr) {
                                already_inserted = true;
                                break;
                        }
                }

                if (!already_inserted)
                        buf[nr++] = bytenr;
        }

        *logical = buf;
        *naddrs = nr;
        *stripe_len = io_stripe_size;
out:
        free_extent_map(em);
        return ret;
}

static int exclude_super_stripes(struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        const bool zoned = btrfs_is_zoned(fs_info);
        u64 bytenr;
        u64 *logical;
        int stripe_len;
        int i, nr, ret;

        if (cache->start < BTRFS_SUPER_INFO_OFFSET) {
                stripe_len = BTRFS_SUPER_INFO_OFFSET - cache->start;
                cache->bytes_super += stripe_len;
                ret = btrfs_add_excluded_extent(fs_info, cache->start,
                                                stripe_len);
                if (ret)
                        return ret;
        }

        for (i = 0; i < BTRFS_SUPER_MIRROR_MAX; i++) {
                bytenr = btrfs_sb_offset(i);
                ret = btrfs_rmap_block(fs_info, cache->start, NULL,
                                       bytenr, &logical, &nr, &stripe_len);
                if (ret)
                        return ret;

                /* Shouldn't have super stripes in sequential zones */
                if (zoned && nr) {
                        btrfs_err(fs_info,
                        "zoned: block group %llu must not contain super block",
                                  cache->start);
                        return -EUCLEAN;
                }

                while (nr--) {
                        u64 len = min_t(u64, stripe_len,
                                cache->start + cache->length - logical[nr]);

                        cache->bytes_super += len;
                        ret = btrfs_add_excluded_extent(fs_info, logical[nr],
                                                        len);
                        if (ret) {
                                kfree(logical);
                                return ret;
                        }
                }

                kfree(logical);
        }
        return 0;
}

static struct btrfs_block_group *btrfs_create_block_group_cache(
                struct btrfs_fs_info *fs_info, u64 start)
{
        struct btrfs_block_group *cache;

        cache = kzalloc(sizeof(*cache), GFP_NOFS);
        if (!cache)
                return NULL;

        cache->free_space_ctl = kzalloc(sizeof(*cache->free_space_ctl),
                                        GFP_NOFS);
        if (!cache->free_space_ctl) {
                kfree(cache);
                return NULL;
        }

        cache->start = start;

        cache->fs_info = fs_info;
        cache->full_stripe_len = btrfs_full_stripe_len(fs_info, start);

        cache->discard_index = BTRFS_DISCARD_INDEX_UNUSED;

        refcount_set(&cache->refs, 1);
        spin_lock_init(&cache->lock);
        init_rwsem(&cache->data_rwsem);
        INIT_LIST_HEAD(&cache->list);
        INIT_LIST_HEAD(&cache->cluster_list);
        INIT_LIST_HEAD(&cache->bg_list);
        INIT_LIST_HEAD(&cache->ro_list);
        INIT_LIST_HEAD(&cache->discard_list);
        INIT_LIST_HEAD(&cache->dirty_list);
        INIT_LIST_HEAD(&cache->io_list);
        INIT_LIST_HEAD(&cache->active_bg_list);
        btrfs_init_free_space_ctl(cache, cache->free_space_ctl);
        atomic_set(&cache->frozen, 0);
        mutex_init(&cache->free_space_lock);
        cache->full_stripe_locks_root.root = RB_ROOT;
        mutex_init(&cache->full_stripe_locks_root.lock);

        return cache;
}

/*
 * Iterate all chunks and verify that each of them has the corresponding block
 * group
 */
static int check_chunk_block_group_mappings(struct btrfs_fs_info *fs_info)
{
        struct extent_map_tree *map_tree = &fs_info->mapping_tree;
        struct extent_map *em;
        struct btrfs_block_group *bg;
        u64 start = 0;
        int ret = 0;

        while (1) {
                read_lock(&map_tree->lock);
                /*
                 * lookup_extent_mapping will return the first extent map
                 * intersecting the range, so setting @len to 1 is enough to
                 * get the first chunk.
                 */
                em = lookup_extent_mapping(map_tree, start, 1);
                read_unlock(&map_tree->lock);
                if (!em)
                        break;

                bg = btrfs_lookup_block_group(fs_info, em->start);
                if (!bg) {
                        btrfs_err(fs_info,
        "chunk start=%llu len=%llu doesn't have corresponding block group",
                                     em->start, em->len);
                        ret = -EUCLEAN;
                        free_extent_map(em);
                        break;
                }
                if (bg->start != em->start || bg->length != em->len ||
                    (bg->flags & BTRFS_BLOCK_GROUP_TYPE_MASK) !=
                    (em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK)) {
                        btrfs_err(fs_info,
"chunk start=%llu len=%llu flags=0x%llx doesn't match block group start=%llu len=%llu flags=0x%llx",
                                em->start, em->len,
                                em->map_lookup->type & BTRFS_BLOCK_GROUP_TYPE_MASK,
                                bg->start, bg->length,
                                bg->flags & BTRFS_BLOCK_GROUP_TYPE_MASK);
                        ret = -EUCLEAN;
                        free_extent_map(em);
                        btrfs_put_block_group(bg);
                        break;
                }
                start = em->start + em->len;
                free_extent_map(em);
                btrfs_put_block_group(bg);
        }
        return ret;
}

static int read_one_block_group(struct btrfs_fs_info *info,
                                struct btrfs_block_group_item *bgi,
                                const struct btrfs_key *key,
                                int need_clear)
{
        struct btrfs_block_group *cache;
        const bool mixed = btrfs_fs_incompat(info, MIXED_GROUPS);
        int ret;

        ASSERT(key->type == BTRFS_BLOCK_GROUP_ITEM_KEY);

        cache = btrfs_create_block_group_cache(info, key->objectid);
        if (!cache)
                return -ENOMEM;

        cache->length = key->offset;
        cache->used = btrfs_stack_block_group_used(bgi);
        cache->commit_used = cache->used;
        cache->flags = btrfs_stack_block_group_flags(bgi);
        cache->global_root_id = btrfs_stack_block_group_chunk_objectid(bgi);

        set_free_space_tree_thresholds(cache);

        if (need_clear) {
                /*
                 * When we mount with old space cache, we need to
                 * set BTRFS_DC_CLEAR and set dirty flag.
                 *
                 * a) Setting 'BTRFS_DC_CLEAR' makes sure that we
                 *    truncate the old free space cache inode and
                 *    setup a new one.
                 * b) Setting 'dirty flag' makes sure that we flush
                 *    the new space cache info onto disk.
                 */
                if (btrfs_test_opt(info, SPACE_CACHE))
                        cache->disk_cache_state = BTRFS_DC_CLEAR;
        }
        if (!mixed && ((cache->flags & BTRFS_BLOCK_GROUP_METADATA) &&
            (cache->flags & BTRFS_BLOCK_GROUP_DATA))) {
                        btrfs_err(info,
"bg %llu is a mixed block group but filesystem hasn't enabled mixed block groups",
                                  cache->start);
                        ret = -EINVAL;
                        goto error;
        }

        ret = btrfs_load_block_group_zone_info(cache, false);
        if (ret) {
                btrfs_err(info, "zoned: failed to load zone info of bg %llu",
                          cache->start);
                goto error;
        }

        /*
         * We need to exclude the super stripes now so that the space info has
         * super bytes accounted for, otherwise we'll think we have more space
         * than we actually do.
         */
        ret = exclude_super_stripes(cache);
        if (ret) {
                /* We may have excluded something, so call this just in case. */
                btrfs_free_excluded_extents(cache);
                goto error;
        }

        /*
         * For zoned filesystem, space after the allocation offset is the only
         * free space for a block group. So, we don't need any caching work.
         * btrfs_calc_zone_unusable() will set the amount of free space and
         * zone_unusable space.
         *
         * For regular filesystem, check for two cases, either we are full, and
         * therefore don't need to bother with the caching work since we won't
         * find any space, or we are empty, and we can just add all the space
         * in and be done with it.  This saves us _a_lot_ of time, particularly
         * in the full case.
         */
        if (btrfs_is_zoned(info)) {
                btrfs_calc_zone_unusable(cache);
                /* Should not have any excluded extents. Just in case, though. */
                btrfs_free_excluded_extents(cache);
        } else if (cache->length == cache->used) {
                cache->cached = BTRFS_CACHE_FINISHED;
                btrfs_free_excluded_extents(cache);
        } else if (cache->used == 0) {
                cache->cached = BTRFS_CACHE_FINISHED;
                add_new_free_space(cache, cache->start,
                                   cache->start + cache->length);
                btrfs_free_excluded_extents(cache);
        }

        ret = btrfs_add_block_group_cache(info, cache);
        if (ret) {
                btrfs_remove_free_space_cache(cache);
                goto error;
        }
        trace_btrfs_add_block_group(info, cache, 0);
        btrfs_add_bg_to_space_info(info, cache);

        set_avail_alloc_bits(info, cache->flags);
        if (btrfs_chunk_writeable(info, cache->start)) {
                if (cache->used == 0) {
                        ASSERT(list_empty(&cache->bg_list));
                        if (btrfs_test_opt(info, DISCARD_ASYNC))
                                btrfs_discard_queue_work(&info->discard_ctl, cache);
                        else
                                btrfs_mark_bg_unused(cache);
                }
        } else {
                inc_block_group_ro(cache, 1);
        }

        return 0;
error:
        btrfs_put_block_group(cache);
        return ret;
}

static int fill_dummy_bgs(struct btrfs_fs_info *fs_info)
{
        struct extent_map_tree *em_tree = &fs_info->mapping_tree;
        struct rb_node *node;
        int ret = 0;

        for (node = rb_first_cached(&em_tree->map); node; node = rb_next(node)) {
                struct extent_map *em;
                struct map_lookup *map;
                struct btrfs_block_group *bg;

                em = rb_entry(node, struct extent_map, rb_node);
                map = em->map_lookup;
                bg = btrfs_create_block_group_cache(fs_info, em->start);
                if (!bg) {
                        ret = -ENOMEM;
                        break;
                }

                /* Fill dummy cache as FULL */
                bg->length = em->len;
                bg->flags = map->type;
                bg->cached = BTRFS_CACHE_FINISHED;
                bg->used = em->len;
                bg->flags = map->type;
                ret = btrfs_add_block_group_cache(fs_info, bg);
                /*
                 * We may have some valid block group cache added already, in
                 * that case we skip to the next one.
                 */
                if (ret == -EEXIST) {
                        ret = 0;
                        btrfs_put_block_group(bg);
                        continue;
                }

                if (ret) {
                        btrfs_remove_free_space_cache(bg);
                        btrfs_put_block_group(bg);
                        break;
                }

                btrfs_add_bg_to_space_info(fs_info, bg);

                set_avail_alloc_bits(fs_info, bg->flags);
        }
        if (!ret)
                btrfs_init_global_block_rsv(fs_info);
        return ret;
}

int btrfs_read_block_groups(struct btrfs_fs_info *info)
{
        struct btrfs_root *root = btrfs_block_group_root(info);
        struct btrfs_path *path;
        int ret;
        struct btrfs_block_group *cache;
        struct btrfs_space_info *space_info;
        struct btrfs_key key;
        int need_clear = 0;
        u64 cache_gen;

        /*
         * Either no extent root (with ibadroots rescue option) or we have
         * unsupported RO options. The fs can never be mounted read-write, so no
         * need to waste time searching block group items.
         *
         * This also allows new extent tree related changes to be RO compat,
         * no need for a full incompat flag.
         */
        if (!root || (btrfs_super_compat_ro_flags(info->super_copy) &
                      ~BTRFS_FEATURE_COMPAT_RO_SUPP))
                return fill_dummy_bgs(info);

        key.objectid = 0;
        key.offset = 0;
        key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        cache_gen = btrfs_super_cache_generation(info->super_copy);
        if (btrfs_test_opt(info, SPACE_CACHE) &&
            btrfs_super_generation(info->super_copy) != cache_gen)
                need_clear = 1;
        if (btrfs_test_opt(info, CLEAR_CACHE))
                need_clear = 1;

        while (1) {
                struct btrfs_block_group_item bgi;
                struct extent_buffer *leaf;
                int slot;

                ret = find_first_block_group(info, path, &key);
                if (ret > 0)
                        break;
                if (ret != 0)
                        goto error;

                leaf = path->nodes[0];
                slot = path->slots[0];

                read_extent_buffer(leaf, &bgi, btrfs_item_ptr_offset(leaf, slot),
                                   sizeof(bgi));

                btrfs_item_key_to_cpu(leaf, &key, slot);
                btrfs_release_path(path);
                ret = read_one_block_group(info, &bgi, &key, need_clear);
                if (ret < 0)
                        goto error;
                key.objectid += key.offset;
                key.offset = 0;
        }
        btrfs_release_path(path);

        list_for_each_entry(space_info, &info->space_info, list) {
                int i;

                for (i = 0; i < BTRFS_NR_RAID_TYPES; i++) {
                        if (list_empty(&space_info->block_groups[i]))
                                continue;
                        cache = list_first_entry(&space_info->block_groups[i],
                                                 struct btrfs_block_group,
                                                 list);
                        btrfs_sysfs_add_block_group_type(cache);
                }

                if (!(btrfs_get_alloc_profile(info, space_info->flags) &
                      (BTRFS_BLOCK_GROUP_RAID10 |
                       BTRFS_BLOCK_GROUP_RAID1_MASK |
                       BTRFS_BLOCK_GROUP_RAID56_MASK |
                       BTRFS_BLOCK_GROUP_DUP)))
                        continue;
                /*
                 * Avoid allocating from un-mirrored block group if there are
                 * mirrored block groups.
                 */
                list_for_each_entry(cache,
                                &space_info->block_groups[BTRFS_RAID_RAID0],
                                list)
                        inc_block_group_ro(cache, 1);
                list_for_each_entry(cache,
                                &space_info->block_groups[BTRFS_RAID_SINGLE],
                                list)
                        inc_block_group_ro(cache, 1);
        }

        btrfs_init_global_block_rsv(info);
        ret = check_chunk_block_group_mappings(info);
error:
        btrfs_free_path(path);
        /*
         * We've hit some error while reading the extent tree, and have
         * rescue=ibadroots mount option.
         * Try to fill the tree using dummy block groups so that the user can
         * continue to mount and grab their data.
         */
        if (ret && btrfs_test_opt(info, IGNOREBADROOTS))
                ret = fill_dummy_bgs(info);
        return ret;
}

/*
 * This function, insert_block_group_item(), belongs to the phase 2 of chunk
 * allocation.
 *
 * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
 * phases.
 */
static int insert_block_group_item(struct btrfs_trans_handle *trans,
                                   struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group_item bgi;
        struct btrfs_root *root = btrfs_block_group_root(fs_info);
        struct btrfs_key key;

        spin_lock(&block_group->lock);
        btrfs_set_stack_block_group_used(&bgi, block_group->used);
        btrfs_set_stack_block_group_chunk_objectid(&bgi,
                                                   block_group->global_root_id);
        btrfs_set_stack_block_group_flags(&bgi, block_group->flags);
        key.objectid = block_group->start;
        key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
        key.offset = block_group->length;
        spin_unlock(&block_group->lock);

        return btrfs_insert_item(trans, root, &key, &bgi, sizeof(bgi));
}

static int insert_dev_extent(struct btrfs_trans_handle *trans,
                            struct btrfs_device *device, u64 chunk_offset,
                            u64 start, u64 num_bytes)
{
        struct btrfs_fs_info *fs_info = device->fs_info;
        struct btrfs_root *root = fs_info->dev_root;
        struct btrfs_path *path;
        struct btrfs_dev_extent *extent;
        struct extent_buffer *leaf;
        struct btrfs_key key;
        int ret;

        WARN_ON(!test_bit(BTRFS_DEV_STATE_IN_FS_METADATA, &device->dev_state));
        WARN_ON(test_bit(BTRFS_DEV_STATE_REPLACE_TGT, &device->dev_state));
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        key.objectid = device->devid;
        key.type = BTRFS_DEV_EXTENT_KEY;
        key.offset = start;
        ret = btrfs_insert_empty_item(trans, root, path, &key, sizeof(*extent));
        if (ret)
                goto out;

        leaf = path->nodes[0];
        extent = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_dev_extent);
        btrfs_set_dev_extent_chunk_tree(leaf, extent, BTRFS_CHUNK_TREE_OBJECTID);
        btrfs_set_dev_extent_chunk_objectid(leaf, extent,
                                            BTRFS_FIRST_CHUNK_TREE_OBJECTID);
        btrfs_set_dev_extent_chunk_offset(leaf, extent, chunk_offset);

        btrfs_set_dev_extent_length(leaf, extent, num_bytes);
        btrfs_mark_buffer_dirty(leaf);
out:
        btrfs_free_path(path);
        return ret;
}

/*
 * This function belongs to phase 2.
 *
 * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
 * phases.
 */
static int insert_dev_extents(struct btrfs_trans_handle *trans,
                                   u64 chunk_offset, u64 chunk_size)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_device *device;
        struct extent_map *em;
        struct map_lookup *map;
        u64 dev_offset;
        u64 stripe_size;
        int i;
        int ret = 0;

        em = btrfs_get_chunk_map(fs_info, chunk_offset, chunk_size);
        if (IS_ERR(em))
                return PTR_ERR(em);

        map = em->map_lookup;
        stripe_size = em->orig_block_len;

        /*
         * Take the device list mutex to prevent races with the final phase of
         * a device replace operation that replaces the device object associated
         * with the map's stripes, because the device object's id can change
         * at any time during that final phase of the device replace operation
         * (dev-replace.c:btrfs_dev_replace_finishing()), so we could grab the
         * replaced device and then see it with an ID of BTRFS_DEV_REPLACE_DEVID,
         * resulting in persisting a device extent item with such ID.
         */
        mutex_lock(&fs_info->fs_devices->device_list_mutex);
        for (i = 0; i < map->num_stripes; i++) {
                device = map->stripes[i].dev;
                dev_offset = map->stripes[i].physical;

                ret = insert_dev_extent(trans, device, chunk_offset, dev_offset,
                                       stripe_size);
                if (ret)
                        break;
        }
        mutex_unlock(&fs_info->fs_devices->device_list_mutex);

        free_extent_map(em);
        return ret;
}

/*
 * This function, btrfs_create_pending_block_groups(), belongs to the phase 2 of
 * chunk allocation.
 *
 * See the comment at btrfs_chunk_alloc() for details about the chunk allocation
 * phases.
 */
void btrfs_create_pending_block_groups(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *block_group;
        int ret = 0;

        while (!list_empty(&trans->new_bgs)) {
                int index;

                block_group = list_first_entry(&trans->new_bgs,
                                               struct btrfs_block_group,
                                               bg_list);
                if (ret)
                        goto next;

                index = btrfs_bg_flags_to_raid_index(block_group->flags);

                ret = insert_block_group_item(trans, block_group);
                if (ret)
                        btrfs_abort_transaction(trans, ret);
                if (!test_bit(BLOCK_GROUP_FLAG_CHUNK_ITEM_INSERTED,
                              &block_group->runtime_flags)) {
                        mutex_lock(&fs_info->chunk_mutex);
                        ret = btrfs_chunk_alloc_add_chunk_item(trans, block_group);
                        mutex_unlock(&fs_info->chunk_mutex);
                        if (ret)
                                btrfs_abort_transaction(trans, ret);
                }
                ret = insert_dev_extents(trans, block_group->start,
                                         block_group->length);
                if (ret)
                        btrfs_abort_transaction(trans, ret);
                add_block_group_free_space(trans, block_group);

                /*
                 * If we restriped during balance, we may have added a new raid
                 * type, so now add the sysfs entries when it is safe to do so.
                 * We don't have to worry about locking here as it's handled in
                 * btrfs_sysfs_add_block_group_type.
                 */
                if (block_group->space_info->block_group_kobjs[index] == NULL)
                        btrfs_sysfs_add_block_group_type(block_group);

                /* Already aborted the transaction if it failed. */
next:
                btrfs_delayed_refs_rsv_release(fs_info, 1);
                list_del_init(&block_group->bg_list);
        }
        btrfs_trans_release_chunk_metadata(trans);
}

/*
 * For extent tree v2 we use the block_group_item->chunk_offset to point at our
 * global root id.  For v1 it's always set to BTRFS_FIRST_CHUNK_TREE_OBJECTID.
 */
static u64 calculate_global_root_id(struct btrfs_fs_info *fs_info, u64 offset)
{
        u64 div = SZ_1G;
        u64 index;

        if (!btrfs_fs_incompat(fs_info, EXTENT_TREE_V2))
                return BTRFS_FIRST_CHUNK_TREE_OBJECTID;

        /* If we have a smaller fs index based on 128MiB. */
        if (btrfs_super_total_bytes(fs_info->super_copy) <= (SZ_1G * 10ULL))
                div = SZ_128M;

        offset = div64_u64(offset, div);
        div64_u64_rem(offset, fs_info->nr_global_roots, &index);
        return index;
}

struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *trans,
                                                 u64 bytes_used, u64 type,
                                                 u64 chunk_offset, u64 size)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *cache;
        int ret;

        btrfs_set_log_full_commit(trans);

        cache = btrfs_create_block_group_cache(fs_info, chunk_offset);
        if (!cache)
                return ERR_PTR(-ENOMEM);

        cache->length = size;
        set_free_space_tree_thresholds(cache);
        cache->used = bytes_used;
        cache->flags = type;
        cache->cached = BTRFS_CACHE_FINISHED;
        cache->global_root_id = calculate_global_root_id(fs_info, cache->start);

        if (btrfs_fs_compat_ro(fs_info, FREE_SPACE_TREE))
                cache->needs_free_space = 1;

        ret = btrfs_load_block_group_zone_info(cache, true);
        if (ret) {
                btrfs_put_block_group(cache);
                return ERR_PTR(ret);
        }

        ret = exclude_super_stripes(cache);
        if (ret) {
                /* We may have excluded something, so call this just in case */
                btrfs_free_excluded_extents(cache);
                btrfs_put_block_group(cache);
                return ERR_PTR(ret);
        }

        add_new_free_space(cache, chunk_offset, chunk_offset + size);

        btrfs_free_excluded_extents(cache);

        /*
         * Ensure the corresponding space_info object is created and
         * assigned to our block group. We want our bg to be added to the rbtree
         * with its ->space_info set.
         */
        cache->space_info = btrfs_find_space_info(fs_info, cache->flags);
        ASSERT(cache->space_info);

        ret = btrfs_add_block_group_cache(fs_info, cache);
        if (ret) {
                btrfs_remove_free_space_cache(cache);
                btrfs_put_block_group(cache);
                return ERR_PTR(ret);
        }

        /*
         * Now that our block group has its ->space_info set and is inserted in
         * the rbtree, update the space info's counters.
         */
        trace_btrfs_add_block_group(fs_info, cache, 1);
        btrfs_add_bg_to_space_info(fs_info, cache);
        btrfs_update_global_block_rsv(fs_info);

#ifdef CONFIG_BTRFS_DEBUG
        if (btrfs_should_fragment_free_space(cache)) {
                u64 new_bytes_used = size - bytes_used;

                cache->space_info->bytes_used += new_bytes_used >> 1;
                fragment_free_space(cache);
        }
#endif

        list_add_tail(&cache->bg_list, &trans->new_bgs);
        trans->delayed_ref_updates++;
        btrfs_update_delayed_refs_rsv(trans);

        set_avail_alloc_bits(fs_info, type);
        return cache;
}

/*
 * Mark one block group RO, can be called several times for the same block
 * group.
 *
 * @cache:              the destination block group
 * @do_chunk_alloc:     whether need to do chunk pre-allocation, this is to
 *                      ensure we still have some free space after marking this
 *                      block group RO.
 */
int btrfs_inc_block_group_ro(struct btrfs_block_group *cache,
                             bool do_chunk_alloc)
{
        struct btrfs_fs_info *fs_info = cache->fs_info;
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = btrfs_block_group_root(fs_info);
        u64 alloc_flags;
        int ret;
        bool dirty_bg_running;

        /*
         * This can only happen when we are doing read-only scrub on read-only
         * mount.
         * In that case we should not start a new transaction on read-only fs.
         * Thus here we skip all chunk allocations.
         */
        if (sb_rdonly(fs_info->sb)) {
                mutex_lock(&fs_info->ro_block_group_mutex);
                ret = inc_block_group_ro(cache, 0);
                mutex_unlock(&fs_info->ro_block_group_mutex);
                return ret;
        }

        do {
                trans = btrfs_join_transaction(root);
                if (IS_ERR(trans))
                        return PTR_ERR(trans);

                dirty_bg_running = false;

                /*
                 * We're not allowed to set block groups readonly after the dirty
                 * block group cache has started writing.  If it already started,
                 * back off and let this transaction commit.
                 */
                mutex_lock(&fs_info->ro_block_group_mutex);
                if (test_bit(BTRFS_TRANS_DIRTY_BG_RUN, &trans->transaction->flags)) {
                        u64 transid = trans->transid;

                        mutex_unlock(&fs_info->ro_block_group_mutex);
                        btrfs_end_transaction(trans);

                        ret = btrfs_wait_for_commit(fs_info, transid);
                        if (ret)
                                return ret;
                        dirty_bg_running = true;
                }
        } while (dirty_bg_running);

        if (do_chunk_alloc) {
                /*
                 * If we are changing raid levels, try to allocate a
                 * corresponding block group with the new raid level.
                 */
                alloc_flags = btrfs_get_alloc_profile(fs_info, cache->flags);
                if (alloc_flags != cache->flags) {
                        ret = btrfs_chunk_alloc(trans, alloc_flags,
                                                CHUNK_ALLOC_FORCE);
                        /*
                         * ENOSPC is allowed here, we may have enough space
                         * already allocated at the new raid level to carry on
                         */
                        if (ret == -ENOSPC)
                                ret = 0;
                        if (ret < 0)
                                goto out;
                }
        }

        ret = inc_block_group_ro(cache, 0);
        if (!do_chunk_alloc || ret == -ETXTBSY)
                goto unlock_out;
        if (!ret)
                goto out;
        alloc_flags = btrfs_get_alloc_profile(fs_info, cache->space_info->flags);
        ret = btrfs_chunk_alloc(trans, alloc_flags, CHUNK_ALLOC_FORCE);
        if (ret < 0)
                goto out;
        /*
         * We have allocated a new chunk. We also need to activate that chunk to
         * grant metadata tickets for zoned filesystem.
         */
        ret = btrfs_zoned_activate_one_bg(fs_info, cache->space_info, true);
        if (ret < 0)
                goto out;

        ret = inc_block_group_ro(cache, 0);
        if (ret == -ETXTBSY)
                goto unlock_out;
out:
        if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
                alloc_flags = btrfs_get_alloc_profile(fs_info, cache->flags);
                mutex_lock(&fs_info->chunk_mutex);
                check_system_chunk(trans, alloc_flags);
                mutex_unlock(&fs_info->chunk_mutex);
        }
unlock_out:
        mutex_unlock(&fs_info->ro_block_group_mutex);

        btrfs_end_transaction(trans);
        return ret;
}

void btrfs_dec_block_group_ro(struct btrfs_block_group *cache)
{
        struct btrfs_space_info *sinfo = cache->space_info;
        u64 num_bytes;

        BUG_ON(!cache->ro);

        spin_lock(&sinfo->lock);
        spin_lock(&cache->lock);
        if (!--cache->ro) {
                if (btrfs_is_zoned(cache->fs_info)) {
                        /* Migrate zone_unusable bytes back */
                        cache->zone_unusable =
                                (cache->alloc_offset - cache->used) +
                                (cache->length - cache->zone_capacity);
                        sinfo->bytes_zone_unusable += cache->zone_unusable;
                        sinfo->bytes_readonly -= cache->zone_unusable;
                }
                num_bytes = cache->length - cache->reserved -
                            cache->pinned - cache->bytes_super -
                            cache->zone_unusable - cache->used;
                sinfo->bytes_readonly -= num_bytes;
                list_del_init(&cache->ro_list);
        }
        spin_unlock(&cache->lock);
        spin_unlock(&sinfo->lock);
}

static int update_block_group_item(struct btrfs_trans_handle *trans,
                                   struct btrfs_path *path,
                                   struct btrfs_block_group *cache)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        int ret;
        struct btrfs_root *root = btrfs_block_group_root(fs_info);
        unsigned long bi;
        struct extent_buffer *leaf;
        struct btrfs_block_group_item bgi;
        struct btrfs_key key;
        u64 old_commit_used;
        u64 used;

        /*
         * Block group items update can be triggered out of commit transaction
         * critical section, thus we need a consistent view of used bytes.
         * We cannot use cache->used directly outside of the spin lock, as it
         * may be changed.
         */
        spin_lock(&cache->lock);
        old_commit_used = cache->commit_used;
        used = cache->used;
        /* No change in used bytes, can safely skip it. */
        if (cache->commit_used == used) {
                spin_unlock(&cache->lock);
                return 0;
        }
        cache->commit_used = used;
        spin_unlock(&cache->lock);

        key.objectid = cache->start;
        key.type = BTRFS_BLOCK_GROUP_ITEM_KEY;
        key.offset = cache->length;

        ret = btrfs_search_slot(trans, root, &key, path, 0, 1);
        if (ret) {
                if (ret > 0)
                        ret = -ENOENT;
                goto fail;
        }

        leaf = path->nodes[0];
        bi = btrfs_item_ptr_offset(leaf, path->slots[0]);
        btrfs_set_stack_block_group_used(&bgi, used);
        btrfs_set_stack_block_group_chunk_objectid(&bgi,
                                                   cache->global_root_id);
        btrfs_set_stack_block_group_flags(&bgi, cache->flags);
        write_extent_buffer(leaf, &bgi, bi, sizeof(bgi));
        btrfs_mark_buffer_dirty(leaf);
fail:
        btrfs_release_path(path);
        /* We didn't update the block group item, need to revert @commit_used. */
        if (ret < 0) {
                spin_lock(&cache->lock);
                cache->commit_used = old_commit_used;
                spin_unlock(&cache->lock);
        }
        return ret;

}

static int cache_save_setup(struct btrfs_block_group *block_group,
                            struct btrfs_trans_handle *trans,
                            struct btrfs_path *path)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct btrfs_root *root = fs_info->tree_root;
        struct inode *inode = NULL;
        struct extent_changeset *data_reserved = NULL;
        u64 alloc_hint = 0;
        int dcs = BTRFS_DC_ERROR;
        u64 cache_size = 0;
        int retries = 0;
        int ret = 0;

        if (!btrfs_test_opt(fs_info, SPACE_CACHE))
                return 0;

        /*
         * If this block group is smaller than 100 megs don't bother caching the
         * block group.
         */
        if (block_group->length < (100 * SZ_1M)) {
                spin_lock(&block_group->lock);
                block_group->disk_cache_state = BTRFS_DC_WRITTEN;
                spin_unlock(&block_group->lock);
                return 0;
        }

        if (TRANS_ABORTED(trans))
                return 0;
again:
        inode = lookup_free_space_inode(block_group, path);
        if (IS_ERR(inode) && PTR_ERR(inode) != -ENOENT) {
                ret = PTR_ERR(inode);
                btrfs_release_path(path);
                goto out;
        }

        if (IS_ERR(inode)) {
                BUG_ON(retries);
                retries++;

                if (block_group->ro)
                        goto out_free;

                ret = create_free_space_inode(trans, block_group, path);
                if (ret)
                        goto out_free;
                goto again;
        }

        /*
         * We want to set the generation to 0, that way if anything goes wrong
         * from here on out we know not to trust this cache when we load up next
         * time.
         */
        BTRFS_I(inode)->generation = 0;
        ret = btrfs_update_inode(trans, root, BTRFS_I(inode));
        if (ret) {
                /*
                 * So theoretically we could recover from this, simply set the
                 * super cache generation to 0 so we know to invalidate the
                 * cache, but then we'd have to keep track of the block groups
                 * that fail this way so we know we _have_ to reset this cache
                 * before the next commit or risk reading stale cache.  So to
                 * limit our exposure to horrible edge cases lets just abort the
                 * transaction, this only happens in really bad situations
                 * anyway.
                 */
                btrfs_abort_transaction(trans, ret);
                goto out_put;
        }
        WARN_ON(ret);

        /* We've already setup this transaction, go ahead and exit */
        if (block_group->cache_generation == trans->transid &&
            i_size_read(inode)) {
                dcs = BTRFS_DC_SETUP;
                goto out_put;
        }

        if (i_size_read(inode) > 0) {
                ret = btrfs_check_trunc_cache_free_space(fs_info,
                                        &fs_info->global_block_rsv);
                if (ret)
                        goto out_put;

                ret = btrfs_truncate_free_space_cache(trans, NULL, inode);
                if (ret)
                        goto out_put;
        }

        spin_lock(&block_group->lock);
        if (block_group->cached != BTRFS_CACHE_FINISHED ||
            !btrfs_test_opt(fs_info, SPACE_CACHE)) {
                /*
                 * don't bother trying to write stuff out _if_
                 * a) we're not cached,
                 * b) we're with nospace_cache mount option,
                 * c) we're with v2 space_cache (FREE_SPACE_TREE).
                 */
                dcs = BTRFS_DC_WRITTEN;
                spin_unlock(&block_group->lock);
                goto out_put;
        }
        spin_unlock(&block_group->lock);

        /*
         * We hit an ENOSPC when setting up the cache in this transaction, just
         * skip doing the setup, we've already cleared the cache so we're safe.
         */
        if (test_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags)) {
                ret = -ENOSPC;
                goto out_put;
        }

        /*
         * Try to preallocate enough space based on how big the block group is.
         * Keep in mind this has to include any pinned space which could end up
         * taking up quite a bit since it's not folded into the other space
         * cache.
         */
        cache_size = div_u64(block_group->length, SZ_256M);
        if (!cache_size)
                cache_size = 1;

        cache_size *= 16;
        cache_size *= fs_info->sectorsize;

        ret = btrfs_check_data_free_space(BTRFS_I(inode), &data_reserved, 0,
                                          cache_size, false);
        if (ret)
                goto out_put;

        ret = btrfs_prealloc_file_range_trans(inode, trans, 0, 0, cache_size,
                                              cache_size, cache_size,
                                              &alloc_hint);
        /*
         * Our cache requires contiguous chunks so that we don't modify a bunch
         * of metadata or split extents when writing the cache out, which means
         * we can enospc if we are heavily fragmented in addition to just normal
         * out of space conditions.  So if we hit this just skip setting up any
         * other block groups for this transaction, maybe we'll unpin enough
         * space the next time around.
         */
        if (!ret)
                dcs = BTRFS_DC_SETUP;
        else if (ret == -ENOSPC)
                set_bit(BTRFS_TRANS_CACHE_ENOSPC, &trans->transaction->flags);

out_put:
        iput(inode);
out_free:
        btrfs_release_path(path);
out:
        spin_lock(&block_group->lock);
        if (!ret && dcs == BTRFS_DC_SETUP)
                block_group->cache_generation = trans->transid;
        block_group->disk_cache_state = dcs;
        spin_unlock(&block_group->lock);

        extent_changeset_free(data_reserved);
        return ret;
}

int btrfs_setup_space_cache(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *cache, *tmp;
        struct btrfs_transaction *cur_trans = trans->transaction;
        struct btrfs_path *path;

        if (list_empty(&cur_trans->dirty_bgs) ||
            !btrfs_test_opt(fs_info, SPACE_CACHE))
                return 0;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /* Could add new block groups, use _safe just in case */
        list_for_each_entry_safe(cache, tmp, &cur_trans->dirty_bgs,
                                 dirty_list) {
                if (cache->disk_cache_state == BTRFS_DC_CLEAR)
                        cache_save_setup(cache, trans, path);
        }

        btrfs_free_path(path);
        return 0;
}

/*
 * Transaction commit does final block group cache writeback during a critical
 * section where nothing is allowed to change the FS.  This is required in
 * order for the cache to actually match the block group, but can introduce a
 * lot of latency into the commit.
 *
 * So, btrfs_start_dirty_block_groups is here to kick off block group cache IO.
 * There's a chance we'll have to redo some of it if the block group changes
 * again during the commit, but it greatly reduces the commit latency by
 * getting rid of the easy block groups while we're still allowing others to
 * join the commit.
 */
int btrfs_start_dirty_block_groups(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *cache;
        struct btrfs_transaction *cur_trans = trans->transaction;
        int ret = 0;
        int should_put;
        struct btrfs_path *path = NULL;
        LIST_HEAD(dirty);
        struct list_head *io = &cur_trans->io_bgs;
        int loops = 0;

        spin_lock(&cur_trans->dirty_bgs_lock);
        if (list_empty(&cur_trans->dirty_bgs)) {
                spin_unlock(&cur_trans->dirty_bgs_lock);
                return 0;
        }
        list_splice_init(&cur_trans->dirty_bgs, &dirty);
        spin_unlock(&cur_trans->dirty_bgs_lock);

again:
        /* Make sure all the block groups on our dirty list actually exist */
        btrfs_create_pending_block_groups(trans);

        if (!path) {
                path = btrfs_alloc_path();
                if (!path) {
                        ret = -ENOMEM;
                        goto out;
                }
        }

        /*
         * cache_write_mutex is here only to save us from balance or automatic
         * removal of empty block groups deleting this block group while we are
         * writing out the cache
         */
        mutex_lock(&trans->transaction->cache_write_mutex);
        while (!list_empty(&dirty)) {
                bool drop_reserve = true;

                cache = list_first_entry(&dirty, struct btrfs_block_group,
                                         dirty_list);
                /*
                 * This can happen if something re-dirties a block group that
                 * is already under IO.  Just wait for it to finish and then do
                 * it all again
                 */
                if (!list_empty(&cache->io_list)) {
                        list_del_init(&cache->io_list);
                        btrfs_wait_cache_io(trans, cache, path);
                        btrfs_put_block_group(cache);
                }


                /*
                 * btrfs_wait_cache_io uses the cache->dirty_list to decide if
                 * it should update the cache_state.  Don't delete until after
                 * we wait.
                 *
                 * Since we're not running in the commit critical section
                 * we need the dirty_bgs_lock to protect from update_block_group
                 */
                spin_lock(&cur_trans->dirty_bgs_lock);
                list_del_init(&cache->dirty_list);
                spin_unlock(&cur_trans->dirty_bgs_lock);

                should_put = 1;

                cache_save_setup(cache, trans, path);

                if (cache->disk_cache_state == BTRFS_DC_SETUP) {
                        cache->io_ctl.inode = NULL;
                        ret = btrfs_write_out_cache(trans, cache, path);
                        if (ret == 0 && cache->io_ctl.inode) {
                                should_put = 0;

                                /*
                                 * The cache_write_mutex is protecting the
                                 * io_list, also refer to the definition of
                                 * btrfs_transaction::io_bgs for more details
                                 */
                                list_add_tail(&cache->io_list, io);
                        } else {
                                /*
                                 * If we failed to write the cache, the
                                 * generation will be bad and life goes on
                                 */
                                ret = 0;
                        }
                }
                if (!ret) {
                        ret = update_block_group_item(trans, path, cache);
                        /*
                         * Our block group might still be attached to the list
                         * of new block groups in the transaction handle of some
                         * other task (struct btrfs_trans_handle->new_bgs). This
                         * means its block group item isn't yet in the extent
                         * tree. If this happens ignore the error, as we will
                         * try again later in the critical section of the
                         * transaction commit.
                         */
                        if (ret == -ENOENT) {
                                ret = 0;
                                spin_lock(&cur_trans->dirty_bgs_lock);
                                if (list_empty(&cache->dirty_list)) {
                                        list_add_tail(&cache->dirty_list,
                                                      &cur_trans->dirty_bgs);
                                        btrfs_get_block_group(cache);
                                        drop_reserve = false;
                                }
                                spin_unlock(&cur_trans->dirty_bgs_lock);
                        } else if (ret) {
                                btrfs_abort_transaction(trans, ret);
                        }
                }

                /* If it's not on the io list, we need to put the block group */
                if (should_put)
                        btrfs_put_block_group(cache);
                if (drop_reserve)
                        btrfs_delayed_refs_rsv_release(fs_info, 1);
                /*
                 * Avoid blocking other tasks for too long. It might even save
                 * us from writing caches for block groups that are going to be
                 * removed.
                 */
                mutex_unlock(&trans->transaction->cache_write_mutex);
                if (ret)
                        goto out;
                mutex_lock(&trans->transaction->cache_write_mutex);
        }
        mutex_unlock(&trans->transaction->cache_write_mutex);

        /*
         * Go through delayed refs for all the stuff we've just kicked off
         * and then loop back (just once)
         */
        if (!ret)
                ret = btrfs_run_delayed_refs(trans, 0);
        if (!ret && loops == 0) {
                loops++;
                spin_lock(&cur_trans->dirty_bgs_lock);
                list_splice_init(&cur_trans->dirty_bgs, &dirty);
                /*
                 * dirty_bgs_lock protects us from concurrent block group
                 * deletes too (not just cache_write_mutex).
                 */
                if (!list_empty(&dirty)) {
                        spin_unlock(&cur_trans->dirty_bgs_lock);
                        goto again;
                }
                spin_unlock(&cur_trans->dirty_bgs_lock);
        }
out:
        if (ret < 0) {
                spin_lock(&cur_trans->dirty_bgs_lock);
                list_splice_init(&dirty, &cur_trans->dirty_bgs);
                spin_unlock(&cur_trans->dirty_bgs_lock);
                btrfs_cleanup_dirty_bgs(cur_trans, fs_info);
        }

        btrfs_free_path(path);
        return ret;
}

int btrfs_write_dirty_block_groups(struct btrfs_trans_handle *trans)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_block_group *cache;
        struct btrfs_transaction *cur_trans = trans->transaction;
        int ret = 0;
        int should_put;
        struct btrfs_path *path;
        struct list_head *io = &cur_trans->io_bgs;

        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;

        /*
         * Even though we are in the critical section of the transaction commit,
         * we can still have concurrent tasks adding elements to this
         * transaction's list of dirty block groups. These tasks correspond to
         * endio free space workers started when writeback finishes for a
         * space cache, which run inode.c:btrfs_finish_ordered_io(), and can
         * allocate new block groups as a result of COWing nodes of the root
         * tree when updating the free space inode. The writeback for the space
         * caches is triggered by an earlier call to
         * btrfs_start_dirty_block_groups() and iterations of the following
         * loop.
         * Also we want to do the cache_save_setup first and then run the
         * delayed refs to make sure we have the best chance at doing this all
         * in one shot.
         */
        spin_lock(&cur_trans->dirty_bgs_lock);
        while (!list_empty(&cur_trans->dirty_bgs)) {
                cache = list_first_entry(&cur_trans->dirty_bgs,
                                         struct btrfs_block_group,
                                         dirty_list);

                /*
                 * This can happen if cache_save_setup re-dirties a block group
                 * that is already under IO.  Just wait for it to finish and
                 * then do it all again
                 */
                if (!list_empty(&cache->io_list)) {
                        spin_unlock(&cur_trans->dirty_bgs_lock);
                        list_del_init(&cache->io_list);
                        btrfs_wait_cache_io(trans, cache, path);
                        btrfs_put_block_group(cache);
                        spin_lock(&cur_trans->dirty_bgs_lock);
                }

                /*
                 * Don't remove from the dirty list until after we've waited on
                 * any pending IO
                 */
                list_del_init(&cache->dirty_list);
                spin_unlock(&cur_trans->dirty_bgs_lock);
                should_put = 1;

                cache_save_setup(cache, trans, path);

                if (!ret)
                        ret = btrfs_run_delayed_refs(trans,
                                                     (unsigned long) -1);

                if (!ret && cache->disk_cache_state == BTRFS_DC_SETUP) {
                        cache->io_ctl.inode = NULL;
                        ret = btrfs_write_out_cache(trans, cache, path);
                        if (ret == 0 && cache->io_ctl.inode) {
                                should_put = 0;
                                list_add_tail(&cache->io_list, io);
                        } else {
                                /*
                                 * If we failed to write the cache, the
                                 * generation will be bad and life goes on
                                 */
                                ret = 0;
                        }
                }
                if (!ret) {
                        ret = update_block_group_item(trans, path, cache);
                        /*
                         * One of the free space endio workers might have
                         * created a new block group while updating a free space
                         * cache's inode (at inode.c:btrfs_finish_ordered_io())
                         * and hasn't released its transaction handle yet, in
                         * which case the new block group is still attached to
                         * its transaction handle and its creation has not
                         * finished yet (no block group item in the extent tree
                         * yet, etc). If this is the case, wait for all free
                         * space endio workers to finish and retry. This is a
                         * very rare case so no need for a more efficient and
                         * complex approach.
                         */
                        if (ret == -ENOENT) {
                                wait_event(cur_trans->writer_wait,
                                   atomic_read(&cur_trans->num_writers) == 1);
                                ret = update_block_group_item(trans, path, cache);
                        }
                        if (ret)
                                btrfs_abort_transaction(trans, ret);
                }

                /* If its not on the io list, we need to put the block group */
                if (should_put)
                        btrfs_put_block_group(cache);
                btrfs_delayed_refs_rsv_release(fs_info, 1);
                spin_lock(&cur_trans->dirty_bgs_lock);
        }
        spin_unlock(&cur_trans->dirty_bgs_lock);

        /*
         * Refer to the definition of io_bgs member for details why it's safe
         * to use it without any locking
         */
        while (!list_empty(io)) {
                cache = list_first_entry(io, struct btrfs_block_group,
                                         io_list);
                list_del_init(&cache->io_list);
                btrfs_wait_cache_io(trans, cache, path);
                btrfs_put_block_group(cache);
        }

        btrfs_free_path(path);
        return ret;
}

int btrfs_update_block_group(struct btrfs_trans_handle *trans,
                             u64 bytenr, u64 num_bytes, bool alloc)
{
        struct btrfs_fs_info *info = trans->fs_info;
        struct btrfs_block_group *cache = NULL;
        u64 total = num_bytes;
        u64 old_val;
        u64 byte_in_group;
        int factor;
        int ret = 0;

        /* Block accounting for super block */
        spin_lock(&info->delalloc_root_lock);
        old_val = btrfs_super_bytes_used(info->super_copy);
        if (alloc)
                old_val += num_bytes;
        else
                old_val -= num_bytes;
        btrfs_set_super_bytes_used(info->super_copy, old_val);
        spin_unlock(&info->delalloc_root_lock);

        while (total) {
                bool reclaim;

                cache = btrfs_lookup_block_group(info, bytenr);
                if (!cache) {
                        ret = -ENOENT;
                        break;
                }
                factor = btrfs_bg_type_to_factor(cache->flags);

                /*
                 * If this block group has free space cache written out, we
                 * need to make sure to load it if we are removing space.  This
                 * is because we need the unpinning stage to actually add the
                 * space back to the block group, otherwise we will leak space.
                 */
                if (!alloc && !btrfs_block_group_done(cache))
                        btrfs_cache_block_group(cache, true);

                byte_in_group = bytenr - cache->start;
                WARN_ON(byte_in_group > cache->length);

                spin_lock(&cache->space_info->lock);
                spin_lock(&cache->lock);

                if (btrfs_test_opt(info, SPACE_CACHE) &&
                    cache->disk_cache_state < BTRFS_DC_CLEAR)
                        cache->disk_cache_state = BTRFS_DC_CLEAR;

                old_val = cache->used;
                num_bytes = min(total, cache->length - byte_in_group);
                if (alloc) {
                        old_val += num_bytes;
                        cache->used = old_val;
                        cache->reserved -= num_bytes;
                        cache->space_info->bytes_reserved -= num_bytes;
                        cache->space_info->bytes_used += num_bytes;
                        cache->space_info->disk_used += num_bytes * factor;
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);
                } else {
                        old_val -= num_bytes;
                        cache->used = old_val;
                        cache->pinned += num_bytes;
                        btrfs_space_info_update_bytes_pinned(info,
                                        cache->space_info, num_bytes);
                        cache->space_info->bytes_used -= num_bytes;
                        cache->space_info->disk_used -= num_bytes * factor;

                        reclaim = should_reclaim_block_group(cache, num_bytes);
                        spin_unlock(&cache->lock);
                        spin_unlock(&cache->space_info->lock);

                        set_extent_dirty(&trans->transaction->pinned_extents,
                                         bytenr, bytenr + num_bytes - 1,
                                         GFP_NOFS | __GFP_NOFAIL);
                }

                spin_lock(&trans->transaction->dirty_bgs_lock);
                if (list_empty(&cache->dirty_list)) {
                        list_add_tail(&cache->dirty_list,
                                      &trans->transaction->dirty_bgs);
                        trans->delayed_ref_updates++;
                        btrfs_get_block_group(cache);
                }
                spin_unlock(&trans->transaction->dirty_bgs_lock);

                /*
                 * No longer have used bytes in this block group, queue it for
                 * deletion. We do this after adding the block group to the
                 * dirty list to avoid races between cleaner kthread and space
                 * cache writeout.
                 */
                if (!alloc && old_val == 0) {
                        if (!btrfs_test_opt(info, DISCARD_ASYNC))
                                btrfs_mark_bg_unused(cache);
                } else if (!alloc && reclaim) {
                        btrfs_mark_bg_to_reclaim(cache);
                }

                btrfs_put_block_group(cache);
                total -= num_bytes;
                bytenr += num_bytes;
        }

        /* Modified block groups are accounted for in the delayed_refs_rsv. */
        btrfs_update_delayed_refs_rsv(trans);
        return ret;
}

/**
 * btrfs_add_reserved_bytes - update the block_group and space info counters
 * @cache:      The cache we are manipulating
 * @ram_bytes:  The number of bytes of file content, and will be same to
 *              @num_bytes except for the compress path.
 * @num_bytes:  The number of bytes in question
 * @delalloc:   The blocks are allocated for the delalloc write
 *
 * This is called by the allocator when it reserves space. If this is a
 * reservation and the block group has become read only we cannot make the
 * reservation and return -EAGAIN, otherwise this function always succeeds.
 */
int btrfs_add_reserved_bytes(struct btrfs_block_group *cache,
                             u64 ram_bytes, u64 num_bytes, int delalloc)
{
        struct btrfs_space_info *space_info = cache->space_info;
        int ret = 0;

        spin_lock(&space_info->lock);
        spin_lock(&cache->lock);
        if (cache->ro) {
                ret = -EAGAIN;
        } else {
                cache->reserved += num_bytes;
                space_info->bytes_reserved += num_bytes;
                trace_btrfs_space_reservation(cache->fs_info, "space_info",
                                              space_info->flags, num_bytes, 1);
                btrfs_space_info_update_bytes_may_use(cache->fs_info,
                                                      space_info, -ram_bytes);
                if (delalloc)
                        cache->delalloc_bytes += num_bytes;

                /*
                 * Compression can use less space than we reserved, so wake
                 * tickets if that happens
                 */
                if (num_bytes < ram_bytes)
                        btrfs_try_granting_tickets(cache->fs_info, space_info);
        }
        spin_unlock(&cache->lock);
        spin_unlock(&space_info->lock);
        return ret;
}

/**
 * btrfs_free_reserved_bytes - update the block_group and space info counters
 * @cache:      The cache we are manipulating
 * @num_bytes:  The number of bytes in question
 * @delalloc:   The blocks are allocated for the delalloc write
 *
 * This is called by somebody who is freeing space that was never actually used
 * on disk.  For example if you reserve some space for a new leaf in transaction
 * A and before transaction A commits you free that leaf, you call this with
 * reserve set to 0 in order to clear the reservation.
 */
void btrfs_free_reserved_bytes(struct btrfs_block_group *cache,
                               u64 num_bytes, int delalloc)
{
        struct btrfs_space_info *space_info = cache->space_info;

        spin_lock(&space_info->lock);
        spin_lock(&cache->lock);
        if (cache->ro)
                space_info->bytes_readonly += num_bytes;
        cache->reserved -= num_bytes;
        space_info->bytes_reserved -= num_bytes;
        space_info->max_extent_size = 0;

        if (delalloc)
                cache->delalloc_bytes -= num_bytes;
        spin_unlock(&cache->lock);

        btrfs_try_granting_tickets(cache->fs_info, space_info);
        spin_unlock(&space_info->lock);
}

static void force_metadata_allocation(struct btrfs_fs_info *info)
{
        struct list_head *head = &info->space_info;
        struct btrfs_space_info *found;

        list_for_each_entry(found, head, list) {
                if (found->flags & BTRFS_BLOCK_GROUP_METADATA)
                        found->force_alloc = CHUNK_ALLOC_FORCE;
        }
}

static int should_alloc_chunk(struct btrfs_fs_info *fs_info,
                              struct btrfs_space_info *sinfo, int force)
{
        u64 bytes_used = btrfs_space_info_used(sinfo, false);
        u64 thresh;

        if (force == CHUNK_ALLOC_FORCE)
                return 1;

        /*
         * in limited mode, we want to have some free space up to
         * about 1% of the FS size.
         */
        if (force == CHUNK_ALLOC_LIMITED) {
                thresh = btrfs_super_total_bytes(fs_info->super_copy);
                thresh = max_t(u64, SZ_64M, div_factor_fine(thresh, 1));

                if (sinfo->total_bytes - bytes_used < thresh)
                        return 1;
        }

        if (bytes_used + SZ_2M < div_factor(sinfo->total_bytes, 8))
                return 0;
        return 1;
}

int btrfs_force_chunk_alloc(struct btrfs_trans_handle *trans, u64 type)
{
        u64 alloc_flags = btrfs_get_alloc_profile(trans->fs_info, type);

        return btrfs_chunk_alloc(trans, alloc_flags, CHUNK_ALLOC_FORCE);
}

static struct btrfs_block_group *do_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags)
{
        struct btrfs_block_group *bg;
        int ret;

        /*
         * Check if we have enough space in the system space info because we
         * will need to update device items in the chunk btree and insert a new
         * chunk item in the chunk btree as well. This will allocate a new
         * system block group if needed.
         */
        check_system_chunk(trans, flags);

        bg = btrfs_create_chunk(trans, flags);
        if (IS_ERR(bg)) {
                ret = PTR_ERR(bg);
                goto out;
        }

        ret = btrfs_chunk_alloc_add_chunk_item(trans, bg);
        /*
         * Normally we are not expected to fail with -ENOSPC here, since we have
         * previously reserved space in the system space_info and allocated one
         * new system chunk if necessary. However there are three exceptions:
         *
         * 1) We may have enough free space in the system space_info but all the
         *    existing system block groups have a profile which can not be used
         *    for extent allocation.
         *
         *    This happens when mounting in degraded mode. For example we have a
         *    RAID1 filesystem with 2 devices, lose one device and mount the fs
         *    using the other device in degraded mode. If we then allocate a chunk,
         *    we may have enough free space in the existing system space_info, but
         *    none of the block groups can be used for extent allocation since they
         *    have a RAID1 profile, and because we are in degraded mode with a
         *    single device, we are forced to allocate a new system chunk with a
         *    SINGLE profile. Making check_system_chunk() iterate over all system
         *    block groups and check if they have a usable profile and enough space
         *    can be slow on very large filesystems, so we tolerate the -ENOSPC and
         *    try again after forcing allocation of a new system chunk. Like this
         *    we avoid paying the cost of that search in normal circumstances, when
         *    we were not mounted in degraded mode;
         *
         * 2) We had enough free space info the system space_info, and one suitable
         *    block group to allocate from when we called check_system_chunk()
         *    above. However right after we called it, the only system block group
         *    with enough free space got turned into RO mode by a running scrub,
         *    and in this case we have to allocate a new one and retry. We only
         *    need do this allocate and retry once, since we have a transaction
         *    handle and scrub uses the commit root to search for block groups;
         *
         * 3) We had one system block group with enough free space when we called
         *    check_system_chunk(), but after that, right before we tried to
         *    allocate the last extent buffer we needed, a discard operation came
         *    in and it temporarily removed the last free space entry from the
         *    block group (discard removes a free space entry, discards it, and
         *    then adds back the entry to the block group cache).
         */
        if (ret == -ENOSPC) {
                const u64 sys_flags = btrfs_system_alloc_profile(trans->fs_info);
                struct btrfs_block_group *sys_bg;

                sys_bg = btrfs_create_chunk(trans, sys_flags);
                if (IS_ERR(sys_bg)) {
                        ret = PTR_ERR(sys_bg);
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                ret = btrfs_chunk_alloc_add_chunk_item(trans, sys_bg);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }

                ret = btrfs_chunk_alloc_add_chunk_item(trans, bg);
                if (ret) {
                        btrfs_abort_transaction(trans, ret);
                        goto out;
                }
        } else if (ret) {
                btrfs_abort_transaction(trans, ret);
                goto out;
        }
out:
        btrfs_trans_release_chunk_metadata(trans);

        if (ret)
                return ERR_PTR(ret);

        btrfs_get_block_group(bg);
        return bg;
}

/*
 * Chunk allocation is done in 2 phases:
 *
 * 1) Phase 1 - through btrfs_chunk_alloc() we allocate device extents for
 *    the chunk, the chunk mapping, create its block group and add the items
 *    that belong in the chunk btree to it - more specifically, we need to
 *    update device items in the chunk btree and add a new chunk item to it.
 *
 * 2) Phase 2 - through btrfs_create_pending_block_groups(), we add the block
 *    group item to the extent btree and the device extent items to the devices
 *    btree.
 *
 * This is done to prevent deadlocks. For example when COWing a node from the
 * extent btree we are holding a write lock on the node's parent and if we
 * trigger chunk allocation and attempted to insert the new block group item
 * in the extent btree right way, we could deadlock because the path for the
 * insertion can include that parent node. At first glance it seems impossible
 * to trigger chunk allocation after starting a transaction since tasks should
 * reserve enough transaction units (metadata space), however while that is true
 * most of the time, chunk allocation may still be triggered for several reasons:
 *
 * 1) When reserving metadata, we check if there is enough free space in the
 *    metadata space_info and therefore don't trigger allocation of a new chunk.
 *    However later when the task actually tries to COW an extent buffer from
 *    the extent btree or from the device btree for example, it is forced to
 *    allocate a new block group (chunk) because the only one that had enough
 *    free space was just turned to RO mode by a running scrub for example (or
 *    device replace, block group reclaim thread, etc), so we can not use it
 *    for allocating an extent and end up being forced to allocate a new one;
 *
 * 2) Because we only check that the metadata space_info has enough free bytes,
 *    we end up not allocating a new metadata chunk in that case. However if
 *    the filesystem was mounted in degraded mode, none of the existing block
 *    groups might be suitable for extent allocation due to their incompatible
 *    profile (for e.g. mounting a 2 devices filesystem, where all block groups
 *    use a RAID1 profile, in degraded mode using a single device). In this case
 *    when the task attempts to COW some extent buffer of the extent btree for
 *    example, it will trigger allocation of a new metadata block group with a
 *    suitable profile (SINGLE profile in the example of the degraded mount of
 *    the RAID1 filesystem);
 *
 * 3) The task has reserved enough transaction units / metadata space, but when
 *    it attempts to COW an extent buffer from the extent or device btree for
 *    example, it does not find any free extent in any metadata block group,
 *    therefore forced to try to allocate a new metadata block group.
 *    This is because some other task allocated all available extents in the
 *    meanwhile - this typically happens with tasks that don't reserve space
 *    properly, either intentionally or as a bug. One example where this is
 *    done intentionally is fsync, as it does not reserve any transaction units
 *    and ends up allocating a variable number of metadata extents for log
 *    tree extent buffers;
 *
 * 4) The task has reserved enough transaction units / metadata space, but right
 *    before it tries to allocate the last extent buffer it needs, a discard
 *    operation comes in and, temporarily, removes the last free space entry from
 *    the only metadata block group that had free space (discard starts by
 *    removing a free space entry from a block group, then does the discard
 *    operation and, once it's done, it adds back the free space entry to the
 *    block group).
 *
 * We also need this 2 phases setup when adding a device to a filesystem with
 * a seed device - we must create new metadata and system chunks without adding
 * any of the block group items to the chunk, extent and device btrees. If we
 * did not do it this way, we would get ENOSPC when attempting to update those
 * btrees, since all the chunks from the seed device are read-only.
 *
 * Phase 1 does the updates and insertions to the chunk btree because if we had
 * it done in phase 2 and have a thundering herd of tasks allocating chunks in
 * parallel, we risk having too many system chunks allocated by many tasks if
 * many tasks reach phase 1 without the previous ones completing phase 2. In the
 * extreme case this leads to exhaustion of the system chunk array in the
 * superblock. This is easier to trigger if using a btree node/leaf size of 64K
 * and with RAID filesystems (so we have more device items in the chunk btree).
 * This has happened before and commit eafa4fd0ad0607 ("btrfs: fix exhaustion of
 * the system chunk array due to concurrent allocations") provides more details.
 *
 * Allocation of system chunks does not happen through this function. A task that
 * needs to update the chunk btree (the only btree that uses system chunks), must
 * preallocate chunk space by calling either check_system_chunk() or
 * btrfs_reserve_chunk_metadata() - the former is used when allocating a data or
 * metadata chunk or when removing a chunk, while the later is used before doing
 * a modification to the chunk btree - use cases for the later are adding,
 * removing and resizing a device as well as relocation of a system chunk.
 * See the comment below for more details.
 *
 * The reservation of system space, done through check_system_chunk(), as well
 * as all the updates and insertions into the chunk btree must be done while
 * holding fs_info->chunk_mutex. This is important to guarantee that while COWing
 * an extent buffer from the chunks btree we never trigger allocation of a new
 * system chunk, which would result in a deadlock (trying to lock twice an
 * extent buffer of the chunk btree, first time before triggering the chunk
 * allocation and the second time during chunk allocation while attempting to
 * update the chunks btree). The system chunk array is also updated while holding
 * that mutex. The same logic applies to removing chunks - we must reserve system
 * space, update the chunk btree and the system chunk array in the superblock
 * while holding fs_info->chunk_mutex.
 *
 * This function, btrfs_chunk_alloc(), belongs to phase 1.
 *
 * If @force is CHUNK_ALLOC_FORCE:
 *    - return 1 if it successfully allocates a chunk,
 *    - return errors including -ENOSPC otherwise.
 * If @force is NOT CHUNK_ALLOC_FORCE:
 *    - return 0 if it doesn't need to allocate a new chunk,
 *    - return 1 if it successfully allocates a chunk,
 *    - return errors including -ENOSPC otherwise.
 */
int btrfs_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags,
                      enum btrfs_chunk_alloc_enum force)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_space_info *space_info;
        struct btrfs_block_group *ret_bg;
        bool wait_for_alloc = false;
        bool should_alloc = false;
        bool from_extent_allocation = false;
        int ret = 0;

        if (force == CHUNK_ALLOC_FORCE_FOR_EXTENT) {
                from_extent_allocation = true;
                force = CHUNK_ALLOC_FORCE;
        }

        /* Don't re-enter if we're already allocating a chunk */
        if (trans->allocating_chunk)
                return -ENOSPC;
        /*
         * Allocation of system chunks can not happen through this path, as we
         * could end up in a deadlock if we are allocating a data or metadata
         * chunk and there is another task modifying the chunk btree.
         *
         * This is because while we are holding the chunk mutex, we will attempt
         * to add the new chunk item to the chunk btree or update an existing
         * device item in the chunk btree, while the other task that is modifying
         * the chunk btree is attempting to COW an extent buffer while holding a
         * lock on it and on its parent - if the COW operation triggers a system
         * chunk allocation, then we can deadlock because we are holding the
         * chunk mutex and we may need to access that extent buffer or its parent
         * in order to add the chunk item or update a device item.
         *
         * Tasks that want to modify the chunk tree should reserve system space
         * before updating the chunk btree, by calling either
         * btrfs_reserve_chunk_metadata() or check_system_chunk().
         * It's possible that after a task reserves the space, it still ends up
         * here - this happens in the cases described above at do_chunk_alloc().
         * The task will have to either retry or fail.
         */
        if (flags & BTRFS_BLOCK_GROUP_SYSTEM)
                return -ENOSPC;

        space_info = btrfs_find_space_info(fs_info, flags);
        ASSERT(space_info);

        do {
                spin_lock(&space_info->lock);
                if (force < space_info->force_alloc)
                        force = space_info->force_alloc;
                should_alloc = should_alloc_chunk(fs_info, space_info, force);
                if (space_info->full) {
                        /* No more free physical space */
                        if (should_alloc)
                                ret = -ENOSPC;
                        else
                                ret = 0;
                        spin_unlock(&space_info->lock);
                        return ret;
                } else if (!should_alloc) {
                        spin_unlock(&space_info->lock);
                        return 0;
                } else if (space_info->chunk_alloc) {
                        /*
                         * Someone is already allocating, so we need to block
                         * until this someone is finished and then loop to
                         * recheck if we should continue with our allocation
                         * attempt.
                         */
                        wait_for_alloc = true;
                        force = CHUNK_ALLOC_NO_FORCE;
                        spin_unlock(&space_info->lock);
                        mutex_lock(&fs_info->chunk_mutex);
                        mutex_unlock(&fs_info->chunk_mutex);
                } else {
                        /* Proceed with allocation */
                        space_info->chunk_alloc = 1;
                        wait_for_alloc = false;
                        spin_unlock(&space_info->lock);
                }

                cond_resched();
        } while (wait_for_alloc);

        mutex_lock(&fs_info->chunk_mutex);
        trans->allocating_chunk = true;

        /*
         * If we have mixed data/metadata chunks we want to make sure we keep
         * allocating mixed chunks instead of individual chunks.
         */
        if (btrfs_mixed_space_info(space_info))
                flags |= (BTRFS_BLOCK_GROUP_DATA | BTRFS_BLOCK_GROUP_METADATA);

        /*
         * if we're doing a data chunk, go ahead and make sure that
         * we keep a reasonable number of metadata chunks allocated in the
         * FS as well.
         */
        if (flags & BTRFS_BLOCK_GROUP_DATA && fs_info->metadata_ratio) {
                fs_info->data_chunk_allocations++;
                if (!(fs_info->data_chunk_allocations %
                      fs_info->metadata_ratio))
                        force_metadata_allocation(fs_info);
        }

        ret_bg = do_chunk_alloc(trans, flags);
        trans->allocating_chunk = false;

        if (IS_ERR(ret_bg)) {
                ret = PTR_ERR(ret_bg);
        } else if (from_extent_allocation) {
                /*
                 * New block group is likely to be used soon. Try to activate
                 * it now. Failure is OK for now.
                 */
                btrfs_zone_activate(ret_bg);
        }

        if (!ret)
                btrfs_put_block_group(ret_bg);

        spin_lock(&space_info->lock);
        if (ret < 0) {
                if (ret == -ENOSPC)
                        space_info->full = 1;
                else
                        goto out;
        } else {
                ret = 1;
                space_info->max_extent_size = 0;
        }

        space_info->force_alloc = CHUNK_ALLOC_NO_FORCE;
out:
        space_info->chunk_alloc = 0;
        spin_unlock(&space_info->lock);
        mutex_unlock(&fs_info->chunk_mutex);

        return ret;
}

static u64 get_profile_num_devs(struct btrfs_fs_info *fs_info, u64 type)
{
        u64 num_dev;

        num_dev = btrfs_raid_array[btrfs_bg_flags_to_raid_index(type)].devs_max;
        if (!num_dev)
                num_dev = fs_info->fs_devices->rw_devices;

        return num_dev;
}

static void reserve_chunk_space(struct btrfs_trans_handle *trans,
                                u64 bytes,
                                u64 type)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        struct btrfs_space_info *info;
        u64 left;
        int ret = 0;

        /*
         * Needed because we can end up allocating a system chunk and for an
         * atomic and race free space reservation in the chunk block reserve.
         */
        lockdep_assert_held(&fs_info->chunk_mutex);

        info = btrfs_find_space_info(fs_info, BTRFS_BLOCK_GROUP_SYSTEM);
        spin_lock(&info->lock);
        left = info->total_bytes - btrfs_space_info_used(info, true);
        spin_unlock(&info->lock);

        if (left < bytes && btrfs_test_opt(fs_info, ENOSPC_DEBUG)) {
                btrfs_info(fs_info, "left=%llu, need=%llu, flags=%llu",
                           left, bytes, type);
                btrfs_dump_space_info(fs_info, info, 0, 0);
        }

        if (left < bytes) {
                u64 flags = btrfs_system_alloc_profile(fs_info);
                struct btrfs_block_group *bg;

                /*
                 * Ignore failure to create system chunk. We might end up not
                 * needing it, as we might not need to COW all nodes/leafs from
                 * the paths we visit in the chunk tree (they were already COWed
                 * or created in the current transaction for example).
                 */
                bg = btrfs_create_chunk(trans, flags);
                if (IS_ERR(bg)) {
                        ret = PTR_ERR(bg);
                } else {
                        /*
                         * We have a new chunk. We also need to activate it for
                         * zoned filesystem.
                         */
                        ret = btrfs_zoned_activate_one_bg(fs_info, info, true);
                        if (ret < 0)
                                return;

                        /*
                         * If we fail to add the chunk item here, we end up
                         * trying again at phase 2 of chunk allocation, at
                         * btrfs_create_pending_block_groups(). So ignore
                         * any error here. An ENOSPC here could happen, due to
                         * the cases described at do_chunk_alloc() - the system
                         * block group we just created was just turned into RO
                         * mode by a scrub for example, or a running discard
                         * temporarily removed its free space entries, etc.
                         */
                        btrfs_chunk_alloc_add_chunk_item(trans, bg);
                }
        }

        if (!ret) {
                ret = btrfs_block_rsv_add(fs_info,
                                          &fs_info->chunk_block_rsv,
                                          bytes, BTRFS_RESERVE_NO_FLUSH);
                if (!ret)
                        trans->chunk_bytes_reserved += bytes;
        }
}

/*
 * Reserve space in the system space for allocating or removing a chunk.
 * The caller must be holding fs_info->chunk_mutex.
 */
void check_system_chunk(struct btrfs_trans_handle *trans, u64 type)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        const u64 num_devs = get_profile_num_devs(fs_info, type);
        u64 bytes;

        /* num_devs device items to update and 1 chunk item to add or remove. */
        bytes = btrfs_calc_metadata_size(fs_info, num_devs) +
                btrfs_calc_insert_metadata_size(fs_info, 1);

        reserve_chunk_space(trans, bytes, type);
}

/*
 * Reserve space in the system space, if needed, for doing a modification to the
 * chunk btree.
 *
 * @trans:              A transaction handle.
 * @is_item_insertion:  Indicate if the modification is for inserting a new item
 *                      in the chunk btree or if it's for the deletion or update
 *                      of an existing item.
 *
 * This is used in a context where we need to update the chunk btree outside
 * block group allocation and removal, to avoid a deadlock with a concurrent
 * task that is allocating a metadata or data block group and therefore needs to
 * update the chunk btree while holding the chunk mutex. After the update to the
 * chunk btree is done, btrfs_trans_release_chunk_metadata() should be called.
 *
 */
void btrfs_reserve_chunk_metadata(struct btrfs_trans_handle *trans,
                                  bool is_item_insertion)
{
        struct btrfs_fs_info *fs_info = trans->fs_info;
        u64 bytes;

        if (is_item_insertion)
                bytes = btrfs_calc_insert_metadata_size(fs_info, 1);
        else
                bytes = btrfs_calc_metadata_size(fs_info, 1);

        mutex_lock(&fs_info->chunk_mutex);
        reserve_chunk_space(trans, bytes, BTRFS_BLOCK_GROUP_SYSTEM);
        mutex_unlock(&fs_info->chunk_mutex);
}

void btrfs_put_block_group_cache(struct btrfs_fs_info *info)
{
        struct btrfs_block_group *block_group;

        block_group = btrfs_lookup_first_block_group(info, 0);
        while (block_group) {
                btrfs_wait_block_group_cache_done(block_group);
                spin_lock(&block_group->lock);
                if (test_and_clear_bit(BLOCK_GROUP_FLAG_IREF,
                                       &block_group->runtime_flags)) {
                        struct inode *inode = block_group->inode;

                        block_group->inode = NULL;
                        spin_unlock(&block_group->lock);

                        ASSERT(block_group->io_ctl.inode == NULL);
                        iput(inode);
                } else {
                        spin_unlock(&block_group->lock);
                }
                block_group = btrfs_next_block_group(block_group);
        }
}

/*
 * Must be called only after stopping all workers, since we could have block
 * group caching kthreads running, and therefore they could race with us if we
 * freed the block groups before stopping them.
 */
int btrfs_free_block_groups(struct btrfs_fs_info *info)
{
        struct btrfs_block_group *block_group;
        struct btrfs_space_info *space_info;
        struct btrfs_caching_control *caching_ctl;
        struct rb_node *n;

        write_lock(&info->block_group_cache_lock);
        while (!list_empty(&info->caching_block_groups)) {
                caching_ctl = list_entry(info->caching_block_groups.next,
                                         struct btrfs_caching_control, list);
                list_del(&caching_ctl->list);
                btrfs_put_caching_control(caching_ctl);
        }
        write_unlock(&info->block_group_cache_lock);

        spin_lock(&info->unused_bgs_lock);
        while (!list_empty(&info->unused_bgs)) {
                block_group = list_first_entry(&info->unused_bgs,
                                               struct btrfs_block_group,
                                               bg_list);
                list_del_init(&block_group->bg_list);
                btrfs_put_block_group(block_group);
        }

        while (!list_empty(&info->reclaim_bgs)) {
                block_group = list_first_entry(&info->reclaim_bgs,
                                               struct btrfs_block_group,
                                               bg_list);
                list_del_init(&block_group->bg_list);
                btrfs_put_block_group(block_group);
        }
        spin_unlock(&info->unused_bgs_lock);

        spin_lock(&info->zone_active_bgs_lock);
        while (!list_empty(&info->zone_active_bgs)) {
                block_group = list_first_entry(&info->zone_active_bgs,
                                               struct btrfs_block_group,
                                               active_bg_list);
                list_del_init(&block_group->active_bg_list);
                btrfs_put_block_group(block_group);
        }
        spin_unlock(&info->zone_active_bgs_lock);

        write_lock(&info->block_group_cache_lock);
        while ((n = rb_last(&info->block_group_cache_tree.rb_root)) != NULL) {
                block_group = rb_entry(n, struct btrfs_block_group,
                                       cache_node);
                rb_erase_cached(&block_group->cache_node,
                                &info->block_group_cache_tree);
                RB_CLEAR_NODE(&block_group->cache_node);
                write_unlock(&info->block_group_cache_lock);

                down_write(&block_group->space_info->groups_sem);
                list_del(&block_group->list);
                up_write(&block_group->space_info->groups_sem);

                /*
                 * We haven't cached this block group, which means we could
                 * possibly have excluded extents on this block group.
                 */
                if (block_group->cached == BTRFS_CACHE_NO ||
                    block_group->cached == BTRFS_CACHE_ERROR)
                        btrfs_free_excluded_extents(block_group);

                btrfs_remove_free_space_cache(block_group);
                ASSERT(block_group->cached != BTRFS_CACHE_STARTED);
                ASSERT(list_empty(&block_group->dirty_list));
                ASSERT(list_empty(&block_group->io_list));
                ASSERT(list_empty(&block_group->bg_list));
                ASSERT(refcount_read(&block_group->refs) == 1);
                ASSERT(block_group->swap_extents == 0);
                btrfs_put_block_group(block_group);

                write_lock(&info->block_group_cache_lock);
        }
        write_unlock(&info->block_group_cache_lock);

        btrfs_release_global_block_rsv(info);

        while (!list_empty(&info->space_info)) {
                space_info = list_entry(info->space_info.next,
                                        struct btrfs_space_info,
                                        list);

                /*
                 * Do not hide this behind enospc_debug, this is actually
                 * important and indicates a real bug if this happens.
                 */
                if (WARN_ON(space_info->bytes_pinned > 0 ||
                            space_info->bytes_may_use > 0))
                        btrfs_dump_space_info(info, space_info, 0, 0);

                /*
                 * If there was a failure to cleanup a log tree, very likely due
                 * to an IO failure on a writeback attempt of one or more of its
                 * extent buffers, we could not do proper (and cheap) unaccounting
                 * of their reserved space, so don't warn on bytes_reserved > 0 in
                 * that case.
                 */
                if (!(space_info->flags & BTRFS_BLOCK_GROUP_METADATA) ||
                    !BTRFS_FS_LOG_CLEANUP_ERROR(info)) {
                        if (WARN_ON(space_info->bytes_reserved > 0))
                                btrfs_dump_space_info(info, space_info, 0, 0);
                }

                WARN_ON(space_info->reclaim_size > 0);
                list_del(&space_info->list);
                btrfs_sysfs_remove_space_info(space_info);
        }
        return 0;
}

void btrfs_freeze_block_group(struct btrfs_block_group *cache)
{
        atomic_inc(&cache->frozen);
}

void btrfs_unfreeze_block_group(struct btrfs_block_group *block_group)
{
        struct btrfs_fs_info *fs_info = block_group->fs_info;
        struct extent_map_tree *em_tree;
        struct extent_map *em;
        bool cleanup;

        spin_lock(&block_group->lock);
        cleanup = (atomic_dec_and_test(&block_group->frozen) &&
                   test_bit(BLOCK_GROUP_FLAG_REMOVED, &block_group->runtime_flags));
        spin_unlock(&block_group->lock);

        if (cleanup) {
                em_tree = &fs_info->mapping_tree;
                write_lock(&em_tree->lock);
                em = lookup_extent_mapping(em_tree, block_group->start,
                                           1);
                BUG_ON(!em); /* logic error, can't happen */
                remove_extent_mapping(em_tree, em);
                write_unlock(&em_tree->lock);

                /* once for us and once for the tree */
                free_extent_map(em);
                free_extent_map(em);

                /*
                 * We may have left one free space entry and other possible
                 * tasks trimming this block group have left 1 entry each one.
                 * Free them if any.
                 */
                btrfs_remove_free_space_cache(block_group);
        }
}

bool btrfs_inc_block_group_swap_extents(struct btrfs_block_group *bg)
{
        bool ret = true;

        spin_lock(&bg->lock);
        if (bg->ro)
                ret = false;
        else
                bg->swap_extents++;
        spin_unlock(&bg->lock);

        return ret;
}

void btrfs_dec_block_group_swap_extents(struct btrfs_block_group *bg, int amount)
{
        spin_lock(&bg->lock);
        ASSERT(!bg->ro);
        ASSERT(bg->swap_extents >= amount);
        bg->swap_extents -= amount;
        spin_unlock(&bg->lock);
}