btrfs: fix race between quota rescan and disable leading to NULL pointer deref

[sfrench/cifs-2.6.git] / fs / inode.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * (C) 1997 Linus Torvalds
 * (C) 1999 Andrea Arcangeli <andrea@suse.de> (dynamic inode allocation)
 */
#include <linux/export.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/backing-dev.h>
#include <linux/hash.h>
#include <linux/swap.h>
#include <linux/security.h>
#include <linux/cdev.h>
#include <linux/memblock.h>
#include <linux/fsnotify.h>
#include <linux/mount.h>
#include <linux/posix_acl.h>
#include <linux/prefetch.h>
#include <linux/buffer_head.h> /* for inode_has_buffers */
#include <linux/ratelimit.h>
#include <linux/list_lru.h>
#include <linux/iversion.h>
#include <trace/events/writeback.h>
#include "internal.h"

/*
 * Inode locking rules:
 *
 * inode->i_lock protects:
 *   inode->i_state, inode->i_hash, __iget(), inode->i_io_list
 * Inode LRU list locks protect:
 *   inode->i_sb->s_inode_lru, inode->i_lru
 * inode->i_sb->s_inode_list_lock protects:
 *   inode->i_sb->s_inodes, inode->i_sb_list
 * bdi->wb.list_lock protects:
 *   bdi->wb.b_{dirty,io,more_io,dirty_time}, inode->i_io_list
 * inode_hash_lock protects:
 *   inode_hashtable, inode->i_hash
 *
 * Lock ordering:
 *
 * inode->i_sb->s_inode_list_lock
 *   inode->i_lock
 *     Inode LRU list locks
 *
 * bdi->wb.list_lock
 *   inode->i_lock
 *
 * inode_hash_lock
 *   inode->i_sb->s_inode_list_lock
 *   inode->i_lock
 *
 * iunique_lock
 *   inode_hash_lock
 */

static unsigned int i_hash_mask __read_mostly;
static unsigned int i_hash_shift __read_mostly;
static struct hlist_head *inode_hashtable __read_mostly;
static __cacheline_aligned_in_smp DEFINE_SPINLOCK(inode_hash_lock);

/*
 * Empty aops. Can be used for the cases where the user does not
 * define any of the address_space operations.
 */
const struct address_space_operations empty_aops = {
};
EXPORT_SYMBOL(empty_aops);

static DEFINE_PER_CPU(unsigned long, nr_inodes);
static DEFINE_PER_CPU(unsigned long, nr_unused);

static struct kmem_cache *inode_cachep __read_mostly;

static long get_nr_inodes(void)
{
        int i;
        long sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_inodes, i);
        return sum < 0 ? 0 : sum;
}

static inline long get_nr_inodes_unused(void)
{
        int i;
        long sum = 0;
        for_each_possible_cpu(i)
                sum += per_cpu(nr_unused, i);
        return sum < 0 ? 0 : sum;
}

long get_nr_dirty_inodes(void)
{
        /* not actually dirty inodes, but a wild approximation */
        long nr_dirty = get_nr_inodes() - get_nr_inodes_unused();
        return nr_dirty > 0 ? nr_dirty : 0;
}

/*
 * Handle nr_inode sysctl
 */
#ifdef CONFIG_SYSCTL
/*
 * Statistics gathering..
 */
static struct inodes_stat_t inodes_stat;

static int proc_nr_inodes(struct ctl_table *table, int write, void *buffer,
                          size_t *lenp, loff_t *ppos)
{
        inodes_stat.nr_inodes = get_nr_inodes();
        inodes_stat.nr_unused = get_nr_inodes_unused();
        return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}

static struct ctl_table inodes_sysctls[] = {
        {
                .procname       = "inode-nr",
                .data           = &inodes_stat,
                .maxlen         = 2*sizeof(long),
                .mode           = 0444,
                .proc_handler   = proc_nr_inodes,
        },
        {
                .procname       = "inode-state",
                .data           = &inodes_stat,
                .maxlen         = 7*sizeof(long),
                .mode           = 0444,
                .proc_handler   = proc_nr_inodes,
        },
        { }
};

static int __init init_fs_inode_sysctls(void)
{
        register_sysctl_init("fs", inodes_sysctls);
        return 0;
}
early_initcall(init_fs_inode_sysctls);
#endif

static int no_open(struct inode *inode, struct file *file)
{
        return -ENXIO;
}

/**
 * inode_init_always - perform inode structure initialisation
 * @sb: superblock inode belongs to
 * @inode: inode to initialise
 *
 * These are initializations that need to be done on every inode
 * allocation as the fields are not initialised by slab allocation.
 */
int inode_init_always(struct super_block *sb, struct inode *inode)
{
        static const struct inode_operations empty_iops;
        static const struct file_operations no_open_fops = {.open = no_open};
        struct address_space *const mapping = &inode->i_data;

        inode->i_sb = sb;
        inode->i_blkbits = sb->s_blocksize_bits;
        inode->i_flags = 0;
        atomic64_set(&inode->i_sequence, 0);
        atomic_set(&inode->i_count, 1);
        inode->i_op = &empty_iops;
        inode->i_fop = &no_open_fops;
        inode->i_ino = 0;
        inode->__i_nlink = 1;
        inode->i_opflags = 0;
        if (sb->s_xattr)
                inode->i_opflags |= IOP_XATTR;
        i_uid_write(inode, 0);
        i_gid_write(inode, 0);
        atomic_set(&inode->i_writecount, 0);
        inode->i_size = 0;
        inode->i_write_hint = WRITE_LIFE_NOT_SET;
        inode->i_blocks = 0;
        inode->i_bytes = 0;
        inode->i_generation = 0;
        inode->i_pipe = NULL;
        inode->i_cdev = NULL;
        inode->i_link = NULL;
        inode->i_dir_seq = 0;
        inode->i_rdev = 0;
        inode->dirtied_when = 0;

#ifdef CONFIG_CGROUP_WRITEBACK
        inode->i_wb_frn_winner = 0;
        inode->i_wb_frn_avg_time = 0;
        inode->i_wb_frn_history = 0;
#endif

        spin_lock_init(&inode->i_lock);
        lockdep_set_class(&inode->i_lock, &sb->s_type->i_lock_key);

        init_rwsem(&inode->i_rwsem);
        lockdep_set_class(&inode->i_rwsem, &sb->s_type->i_mutex_key);

        atomic_set(&inode->i_dio_count, 0);

        mapping->a_ops = &empty_aops;
        mapping->host = inode;
        mapping->flags = 0;
        mapping->wb_err = 0;
        atomic_set(&mapping->i_mmap_writable, 0);
#ifdef CONFIG_READ_ONLY_THP_FOR_FS
        atomic_set(&mapping->nr_thps, 0);
#endif
        mapping_set_gfp_mask(mapping, GFP_HIGHUSER_MOVABLE);
        mapping->private_data = NULL;
        mapping->writeback_index = 0;
        init_rwsem(&mapping->invalidate_lock);
        lockdep_set_class_and_name(&mapping->invalidate_lock,
                                   &sb->s_type->invalidate_lock_key,
                                   "mapping.invalidate_lock");
        inode->i_private = NULL;
        inode->i_mapping = mapping;
        INIT_HLIST_HEAD(&inode->i_dentry);      /* buggered by rcu freeing */
#ifdef CONFIG_FS_POSIX_ACL
        inode->i_acl = inode->i_default_acl = ACL_NOT_CACHED;
#endif

#ifdef CONFIG_FSNOTIFY
        inode->i_fsnotify_mask = 0;
#endif
        inode->i_flctx = NULL;

        if (unlikely(security_inode_alloc(inode)))
                return -ENOMEM;
        this_cpu_inc(nr_inodes);

        return 0;
}
EXPORT_SYMBOL(inode_init_always);

void free_inode_nonrcu(struct inode *inode)
{
        kmem_cache_free(inode_cachep, inode);
}
EXPORT_SYMBOL(free_inode_nonrcu);

static void i_callback(struct rcu_head *head)
{
        struct inode *inode = container_of(head, struct inode, i_rcu);
        if (inode->free_inode)
                inode->free_inode(inode);
        else
                free_inode_nonrcu(inode);
}

static struct inode *alloc_inode(struct super_block *sb)
{
        const struct super_operations *ops = sb->s_op;
        struct inode *inode;

        if (ops->alloc_inode)
                inode = ops->alloc_inode(sb);
        else
                inode = alloc_inode_sb(sb, inode_cachep, GFP_KERNEL);

        if (!inode)
                return NULL;

        if (unlikely(inode_init_always(sb, inode))) {
                if (ops->destroy_inode) {
                        ops->destroy_inode(inode);
                        if (!ops->free_inode)
                                return NULL;
                }
                inode->free_inode = ops->free_inode;
                i_callback(&inode->i_rcu);
                return NULL;
        }

        return inode;
}

void __destroy_inode(struct inode *inode)
{
        BUG_ON(inode_has_buffers(inode));
        inode_detach_wb(inode);
        security_inode_free(inode);
        fsnotify_inode_delete(inode);
        locks_free_lock_context(inode);
        if (!inode->i_nlink) {
                WARN_ON(atomic_long_read(&inode->i_sb->s_remove_count) == 0);
                atomic_long_dec(&inode->i_sb->s_remove_count);
        }

#ifdef CONFIG_FS_POSIX_ACL
        if (inode->i_acl && !is_uncached_acl(inode->i_acl))
                posix_acl_release(inode->i_acl);
        if (inode->i_default_acl && !is_uncached_acl(inode->i_default_acl))
                posix_acl_release(inode->i_default_acl);
#endif
        this_cpu_dec(nr_inodes);
}
EXPORT_SYMBOL(__destroy_inode);

static void destroy_inode(struct inode *inode)
{
        const struct super_operations *ops = inode->i_sb->s_op;

        BUG_ON(!list_empty(&inode->i_lru));
        __destroy_inode(inode);
        if (ops->destroy_inode) {
                ops->destroy_inode(inode);
                if (!ops->free_inode)
                        return;
        }
        inode->free_inode = ops->free_inode;
        call_rcu(&inode->i_rcu, i_callback);
}

/**
 * drop_nlink - directly drop an inode's link count
 * @inode: inode
 *
 * This is a low-level filesystem helper to replace any
 * direct filesystem manipulation of i_nlink.  In cases
 * where we are attempting to track writes to the
 * filesystem, a decrement to zero means an imminent
 * write when the file is truncated and actually unlinked
 * on the filesystem.
 */
void drop_nlink(struct inode *inode)
{
        WARN_ON(inode->i_nlink == 0);
        inode->__i_nlink--;
        if (!inode->i_nlink)
                atomic_long_inc(&inode->i_sb->s_remove_count);
}
EXPORT_SYMBOL(drop_nlink);

/**
 * clear_nlink - directly zero an inode's link count
 * @inode: inode
 *
 * This is a low-level filesystem helper to replace any
 * direct filesystem manipulation of i_nlink.  See
 * drop_nlink() for why we care about i_nlink hitting zero.
 */
void clear_nlink(struct inode *inode)
{
        if (inode->i_nlink) {
                inode->__i_nlink = 0;
                atomic_long_inc(&inode->i_sb->s_remove_count);
        }
}
EXPORT_SYMBOL(clear_nlink);

/**
 * set_nlink - directly set an inode's link count
 * @inode: inode
 * @nlink: new nlink (should be non-zero)
 *
 * This is a low-level filesystem helper to replace any
 * direct filesystem manipulation of i_nlink.
 */
void set_nlink(struct inode *inode, unsigned int nlink)
{
        if (!nlink) {
                clear_nlink(inode);
        } else {
                /* Yes, some filesystems do change nlink from zero to one */
                if (inode->i_nlink == 0)
                        atomic_long_dec(&inode->i_sb->s_remove_count);

                inode->__i_nlink = nlink;
        }
}
EXPORT_SYMBOL(set_nlink);

/**
 * inc_nlink - directly increment an inode's link count
 * @inode: inode
 *
 * This is a low-level filesystem helper to replace any
 * direct filesystem manipulation of i_nlink.  Currently,
 * it is only here for parity with dec_nlink().
 */
void inc_nlink(struct inode *inode)
{
        if (unlikely(inode->i_nlink == 0)) {
                WARN_ON(!(inode->i_state & I_LINKABLE));
                atomic_long_dec(&inode->i_sb->s_remove_count);
        }

        inode->__i_nlink++;
}
EXPORT_SYMBOL(inc_nlink);

static void __address_space_init_once(struct address_space *mapping)
{
        xa_init_flags(&mapping->i_pages, XA_FLAGS_LOCK_IRQ | XA_FLAGS_ACCOUNT);
        init_rwsem(&mapping->i_mmap_rwsem);
        INIT_LIST_HEAD(&mapping->private_list);
        spin_lock_init(&mapping->private_lock);
        mapping->i_mmap = RB_ROOT_CACHED;
}

void address_space_init_once(struct address_space *mapping)
{
        memset(mapping, 0, sizeof(*mapping));
        __address_space_init_once(mapping);
}
EXPORT_SYMBOL(address_space_init_once);

/*
 * These are initializations that only need to be done
 * once, because the fields are idempotent across use
 * of the inode, so let the slab aware of that.
 */
void inode_init_once(struct inode *inode)
{
        memset(inode, 0, sizeof(*inode));
        INIT_HLIST_NODE(&inode->i_hash);
        INIT_LIST_HEAD(&inode->i_devices);
        INIT_LIST_HEAD(&inode->i_io_list);
        INIT_LIST_HEAD(&inode->i_wb_list);
        INIT_LIST_HEAD(&inode->i_lru);
        INIT_LIST_HEAD(&inode->i_sb_list);
        __address_space_init_once(&inode->i_data);
        i_size_ordered_init(inode);
}
EXPORT_SYMBOL(inode_init_once);

static void init_once(void *foo)
{
        struct inode *inode = (struct inode *) foo;

        inode_init_once(inode);
}

/*
 * inode->i_lock must be held
 */
void __iget(struct inode *inode)
{
        atomic_inc(&inode->i_count);
}

/*
 * get additional reference to inode; caller must already hold one.
 */
void ihold(struct inode *inode)
{
        WARN_ON(atomic_inc_return(&inode->i_count) < 2);
}
EXPORT_SYMBOL(ihold);

static void __inode_add_lru(struct inode *inode, bool rotate)
{
        if (inode->i_state & (I_DIRTY_ALL | I_SYNC | I_FREEING | I_WILL_FREE))
                return;
        if (atomic_read(&inode->i_count))
                return;
        if (!(inode->i_sb->s_flags & SB_ACTIVE))
                return;
        if (!mapping_shrinkable(&inode->i_data))
                return;

        if (list_lru_add(&inode->i_sb->s_inode_lru, &inode->i_lru))
                this_cpu_inc(nr_unused);
        else if (rotate)
                inode->i_state |= I_REFERENCED;
}

/*
 * Add inode to LRU if needed (inode is unused and clean).
 *
 * Needs inode->i_lock held.
 */
void inode_add_lru(struct inode *inode)
{
        __inode_add_lru(inode, false);
}

static void inode_lru_list_del(struct inode *inode)
{
        if (list_lru_del(&inode->i_sb->s_inode_lru, &inode->i_lru))
                this_cpu_dec(nr_unused);
}

/**
 * inode_sb_list_add - add inode to the superblock list of inodes
 * @inode: inode to add
 */
void inode_sb_list_add(struct inode *inode)
{
        spin_lock(&inode->i_sb->s_inode_list_lock);
        list_add(&inode->i_sb_list, &inode->i_sb->s_inodes);
        spin_unlock(&inode->i_sb->s_inode_list_lock);
}
EXPORT_SYMBOL_GPL(inode_sb_list_add);

static inline void inode_sb_list_del(struct inode *inode)
{
        if (!list_empty(&inode->i_sb_list)) {
                spin_lock(&inode->i_sb->s_inode_list_lock);
                list_del_init(&inode->i_sb_list);
                spin_unlock(&inode->i_sb->s_inode_list_lock);
        }
}

static unsigned long hash(struct super_block *sb, unsigned long hashval)
{
        unsigned long tmp;

        tmp = (hashval * (unsigned long)sb) ^ (GOLDEN_RATIO_PRIME + hashval) /
                        L1_CACHE_BYTES;
        tmp = tmp ^ ((tmp ^ GOLDEN_RATIO_PRIME) >> i_hash_shift);
        return tmp & i_hash_mask;
}

/**
 *      __insert_inode_hash - hash an inode
 *      @inode: unhashed inode
 *      @hashval: unsigned long value used to locate this object in the
 *              inode_hashtable.
 *
 *      Add an inode to the inode hash for this superblock.
 */
void __insert_inode_hash(struct inode *inode, unsigned long hashval)
{
        struct hlist_head *b = inode_hashtable + hash(inode->i_sb, hashval);

        spin_lock(&inode_hash_lock);
        spin_lock(&inode->i_lock);
        hlist_add_head_rcu(&inode->i_hash, b);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_lock);
}
EXPORT_SYMBOL(__insert_inode_hash);

/**
 *      __remove_inode_hash - remove an inode from the hash
 *      @inode: inode to unhash
 *
 *      Remove an inode from the superblock.
 */
void __remove_inode_hash(struct inode *inode)
{
        spin_lock(&inode_hash_lock);
        spin_lock(&inode->i_lock);
        hlist_del_init_rcu(&inode->i_hash);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_lock);
}
EXPORT_SYMBOL(__remove_inode_hash);

void dump_mapping(const struct address_space *mapping)
{
        struct inode *host;
        const struct address_space_operations *a_ops;
        struct hlist_node *dentry_first;
        struct dentry *dentry_ptr;
        struct dentry dentry;
        unsigned long ino;

        /*
         * If mapping is an invalid pointer, we don't want to crash
         * accessing it, so probe everything depending on it carefully.
         */
        if (get_kernel_nofault(host, &mapping->host) ||
            get_kernel_nofault(a_ops, &mapping->a_ops)) {
                pr_warn("invalid mapping:%px\n", mapping);
                return;
        }

        if (!host) {
                pr_warn("aops:%ps\n", a_ops);
                return;
        }

        if (get_kernel_nofault(dentry_first, &host->i_dentry.first) ||
            get_kernel_nofault(ino, &host->i_ino)) {
                pr_warn("aops:%ps invalid inode:%px\n", a_ops, host);
                return;
        }

        if (!dentry_first) {
                pr_warn("aops:%ps ino:%lx\n", a_ops, ino);
                return;
        }

        dentry_ptr = container_of(dentry_first, struct dentry, d_u.d_alias);
        if (get_kernel_nofault(dentry, dentry_ptr)) {
                pr_warn("aops:%ps ino:%lx invalid dentry:%px\n",
                                a_ops, ino, dentry_ptr);
                return;
        }

        /*
         * if dentry is corrupted, the %pd handler may still crash,
         * but it's unlikely that we reach here with a corrupt mapping
         */
        pr_warn("aops:%ps ino:%lx dentry name:\"%pd\"\n", a_ops, ino, &dentry);
}

void clear_inode(struct inode *inode)
{
        /*
         * We have to cycle the i_pages lock here because reclaim can be in the
         * process of removing the last page (in __filemap_remove_folio())
         * and we must not free the mapping under it.
         */
        xa_lock_irq(&inode->i_data.i_pages);
        BUG_ON(inode->i_data.nrpages);
        /*
         * Almost always, mapping_empty(&inode->i_data) here; but there are
         * two known and long-standing ways in which nodes may get left behind
         * (when deep radix-tree node allocation failed partway; or when THP
         * collapse_file() failed). Until those two known cases are cleaned up,
         * or a cleanup function is called here, do not BUG_ON(!mapping_empty),
         * nor even WARN_ON(!mapping_empty).
         */
        xa_unlock_irq(&inode->i_data.i_pages);
        BUG_ON(!list_empty(&inode->i_data.private_list));
        BUG_ON(!(inode->i_state & I_FREEING));
        BUG_ON(inode->i_state & I_CLEAR);
        BUG_ON(!list_empty(&inode->i_wb_list));
        /* don't need i_lock here, no concurrent mods to i_state */
        inode->i_state = I_FREEING | I_CLEAR;
}
EXPORT_SYMBOL(clear_inode);

/*
 * Free the inode passed in, removing it from the lists it is still connected
 * to. We remove any pages still attached to the inode and wait for any IO that
 * is still in progress before finally destroying the inode.
 *
 * An inode must already be marked I_FREEING so that we avoid the inode being
 * moved back onto lists if we race with other code that manipulates the lists
 * (e.g. writeback_single_inode). The caller is responsible for setting this.
 *
 * An inode must already be removed from the LRU list before being evicted from
 * the cache. This should occur atomically with setting the I_FREEING state
 * flag, so no inodes here should ever be on the LRU when being evicted.
 */
static void evict(struct inode *inode)
{
        const struct super_operations *op = inode->i_sb->s_op;

        BUG_ON(!(inode->i_state & I_FREEING));
        BUG_ON(!list_empty(&inode->i_lru));

        if (!list_empty(&inode->i_io_list))
                inode_io_list_del(inode);

        inode_sb_list_del(inode);

        /*
         * Wait for flusher thread to be done with the inode so that filesystem
         * does not start destroying it while writeback is still running. Since
         * the inode has I_FREEING set, flusher thread won't start new work on
         * the inode.  We just have to wait for running writeback to finish.
         */
        inode_wait_for_writeback(inode);

        if (op->evict_inode) {
                op->evict_inode(inode);
        } else {
                truncate_inode_pages_final(&inode->i_data);
                clear_inode(inode);
        }
        if (S_ISCHR(inode->i_mode) && inode->i_cdev)
                cd_forget(inode);

        remove_inode_hash(inode);

        spin_lock(&inode->i_lock);
        wake_up_bit(&inode->i_state, __I_NEW);
        BUG_ON(inode->i_state != (I_FREEING | I_CLEAR));
        spin_unlock(&inode->i_lock);

        destroy_inode(inode);
}

/*
 * dispose_list - dispose of the contents of a local list
 * @head: the head of the list to free
 *
 * Dispose-list gets a local list with local inodes in it, so it doesn't
 * need to worry about list corruption and SMP locks.
 */
static void dispose_list(struct list_head *head)
{
        while (!list_empty(head)) {
                struct inode *inode;

                inode = list_first_entry(head, struct inode, i_lru);
                list_del_init(&inode->i_lru);

                evict(inode);
                cond_resched();
        }
}

/**
 * evict_inodes - evict all evictable inodes for a superblock
 * @sb:         superblock to operate on
 *
 * Make sure that no inodes with zero refcount are retained.  This is
 * called by superblock shutdown after having SB_ACTIVE flag removed,
 * so any inode reaching zero refcount during or after that call will
 * be immediately evicted.
 */
void evict_inodes(struct super_block *sb)
{
        struct inode *inode, *next;
        LIST_HEAD(dispose);

again:
        spin_lock(&sb->s_inode_list_lock);
        list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                if (atomic_read(&inode->i_count))
                        continue;

                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }

                inode->i_state |= I_FREEING;
                inode_lru_list_del(inode);
                spin_unlock(&inode->i_lock);
                list_add(&inode->i_lru, &dispose);

                /*
                 * We can have a ton of inodes to evict at unmount time given
                 * enough memory, check to see if we need to go to sleep for a
                 * bit so we don't livelock.
                 */
                if (need_resched()) {
                        spin_unlock(&sb->s_inode_list_lock);
                        cond_resched();
                        dispose_list(&dispose);
                        goto again;
                }
        }
        spin_unlock(&sb->s_inode_list_lock);

        dispose_list(&dispose);
}
EXPORT_SYMBOL_GPL(evict_inodes);

/**
 * invalidate_inodes    - attempt to free all inodes on a superblock
 * @sb:         superblock to operate on
 * @kill_dirty: flag to guide handling of dirty inodes
 *
 * Attempts to free all inodes for a given superblock.  If there were any
 * busy inodes return a non-zero value, else zero.
 * If @kill_dirty is set, discard dirty inodes too, otherwise treat
 * them as busy.
 */
int invalidate_inodes(struct super_block *sb, bool kill_dirty)
{
        int busy = 0;
        struct inode *inode, *next;
        LIST_HEAD(dispose);

again:
        spin_lock(&sb->s_inode_list_lock);
        list_for_each_entry_safe(inode, next, &sb->s_inodes, i_sb_list) {
                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
                        spin_unlock(&inode->i_lock);
                        continue;
                }
                if (inode->i_state & I_DIRTY_ALL && !kill_dirty) {
                        spin_unlock(&inode->i_lock);
                        busy = 1;
                        continue;
                }
                if (atomic_read(&inode->i_count)) {
                        spin_unlock(&inode->i_lock);
                        busy = 1;
                        continue;
                }

                inode->i_state |= I_FREEING;
                inode_lru_list_del(inode);
                spin_unlock(&inode->i_lock);
                list_add(&inode->i_lru, &dispose);
                if (need_resched()) {
                        spin_unlock(&sb->s_inode_list_lock);
                        cond_resched();
                        dispose_list(&dispose);
                        goto again;
                }
        }
        spin_unlock(&sb->s_inode_list_lock);

        dispose_list(&dispose);

        return busy;
}

/*
 * Isolate the inode from the LRU in preparation for freeing it.
 *
 * If the inode has the I_REFERENCED flag set, then it means that it has been
 * used recently - the flag is set in iput_final(). When we encounter such an
 * inode, clear the flag and move it to the back of the LRU so it gets another
 * pass through the LRU before it gets reclaimed. This is necessary because of
 * the fact we are doing lazy LRU updates to minimise lock contention so the
 * LRU does not have strict ordering. Hence we don't want to reclaim inodes
 * with this flag set because they are the inodes that are out of order.
 */
static enum lru_status inode_lru_isolate(struct list_head *item,
                struct list_lru_one *lru, spinlock_t *lru_lock, void *arg)
{
        struct list_head *freeable = arg;
        struct inode    *inode = container_of(item, struct inode, i_lru);

        /*
         * We are inverting the lru lock/inode->i_lock here, so use a
         * trylock. If we fail to get the lock, just skip it.
         */
        if (!spin_trylock(&inode->i_lock))
                return LRU_SKIP;

        /*
         * Inodes can get referenced, redirtied, or repopulated while
         * they're already on the LRU, and this can make them
         * unreclaimable for a while. Remove them lazily here; iput,
         * sync, or the last page cache deletion will requeue them.
         */
        if (atomic_read(&inode->i_count) ||
            (inode->i_state & ~I_REFERENCED) ||
            !mapping_shrinkable(&inode->i_data)) {
                list_lru_isolate(lru, &inode->i_lru);
                spin_unlock(&inode->i_lock);
                this_cpu_dec(nr_unused);
                return LRU_REMOVED;
        }

        /* Recently referenced inodes get one more pass */
        if (inode->i_state & I_REFERENCED) {
                inode->i_state &= ~I_REFERENCED;
                spin_unlock(&inode->i_lock);
                return LRU_ROTATE;
        }

        /*
         * On highmem systems, mapping_shrinkable() permits dropping
         * page cache in order to free up struct inodes: lowmem might
         * be under pressure before the cache inside the highmem zone.
         */
        if (inode_has_buffers(inode) || !mapping_empty(&inode->i_data)) {
                __iget(inode);
                spin_unlock(&inode->i_lock);
                spin_unlock(lru_lock);
                if (remove_inode_buffers(inode)) {
                        unsigned long reap;
                        reap = invalidate_mapping_pages(&inode->i_data, 0, -1);
                        if (current_is_kswapd())
                                __count_vm_events(KSWAPD_INODESTEAL, reap);
                        else
                                __count_vm_events(PGINODESTEAL, reap);
                        if (current->reclaim_state)
                                current->reclaim_state->reclaimed_slab += reap;
                }
                iput(inode);
                spin_lock(lru_lock);
                return LRU_RETRY;
        }

        WARN_ON(inode->i_state & I_NEW);
        inode->i_state |= I_FREEING;
        list_lru_isolate_move(lru, &inode->i_lru, freeable);
        spin_unlock(&inode->i_lock);

        this_cpu_dec(nr_unused);
        return LRU_REMOVED;
}

/*
 * Walk the superblock inode LRU for freeable inodes and attempt to free them.
 * This is called from the superblock shrinker function with a number of inodes
 * to trim from the LRU. Inodes to be freed are moved to a temporary list and
 * then are freed outside inode_lock by dispose_list().
 */
long prune_icache_sb(struct super_block *sb, struct shrink_control *sc)
{
        LIST_HEAD(freeable);
        long freed;

        freed = list_lru_shrink_walk(&sb->s_inode_lru, sc,
                                     inode_lru_isolate, &freeable);
        dispose_list(&freeable);
        return freed;
}

static void __wait_on_freeing_inode(struct inode *inode);
/*
 * Called with the inode lock held.
 */
static struct inode *find_inode(struct super_block *sb,
                                struct hlist_head *head,
                                int (*test)(struct inode *, void *),
                                void *data)
{
        struct inode *inode = NULL;

repeat:
        hlist_for_each_entry(inode, head, i_hash) {
                if (inode->i_sb != sb)
                        continue;
                if (!test(inode, data))
                        continue;
                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                if (unlikely(inode->i_state & I_CREATING)) {
                        spin_unlock(&inode->i_lock);
                        return ERR_PTR(-ESTALE);
                }
                __iget(inode);
                spin_unlock(&inode->i_lock);
                return inode;
        }
        return NULL;
}

/*
 * find_inode_fast is the fast path version of find_inode, see the comment at
 * iget_locked for details.
 */
static struct inode *find_inode_fast(struct super_block *sb,
                                struct hlist_head *head, unsigned long ino)
{
        struct inode *inode = NULL;

repeat:
        hlist_for_each_entry(inode, head, i_hash) {
                if (inode->i_ino != ino)
                        continue;
                if (inode->i_sb != sb)
                        continue;
                spin_lock(&inode->i_lock);
                if (inode->i_state & (I_FREEING|I_WILL_FREE)) {
                        __wait_on_freeing_inode(inode);
                        goto repeat;
                }
                if (unlikely(inode->i_state & I_CREATING)) {
                        spin_unlock(&inode->i_lock);
                        return ERR_PTR(-ESTALE);
                }
                __iget(inode);
                spin_unlock(&inode->i_lock);
                return inode;
        }
        return NULL;
}

/*
 * Each cpu owns a range of LAST_INO_BATCH numbers.
 * 'shared_last_ino' is dirtied only once out of LAST_INO_BATCH allocations,
 * to renew the exhausted range.
 *
 * This does not significantly increase overflow rate because every CPU can
 * consume at most LAST_INO_BATCH-1 unused inode numbers. So there is
 * NR_CPUS*(LAST_INO_BATCH-1) wastage. At 4096 and 1024, this is ~0.1% of the
 * 2^32 range, and is a worst-case. Even a 50% wastage would only increase
 * overflow rate by 2x, which does not seem too significant.
 *
 * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
 * error if st_ino won't fit in target struct field. Use 32bit counter
 * here to attempt to avoid that.
 */
#define LAST_INO_BATCH 1024
static DEFINE_PER_CPU(unsigned int, last_ino);

unsigned int get_next_ino(void)
{
        unsigned int *p = &get_cpu_var(last_ino);
        unsigned int res = *p;

#ifdef CONFIG_SMP
        if (unlikely((res & (LAST_INO_BATCH-1)) == 0)) {
                static atomic_t shared_last_ino;
                int next = atomic_add_return(LAST_INO_BATCH, &shared_last_ino);

                res = next - LAST_INO_BATCH;
        }
#endif

        res++;
        /* get_next_ino should not provide a 0 inode number */
        if (unlikely(!res))
                res++;
        *p = res;
        put_cpu_var(last_ino);
        return res;
}
EXPORT_SYMBOL(get_next_ino);

/**
 *      new_inode_pseudo        - obtain an inode
 *      @sb: superblock
 *
 *      Allocates a new inode for given superblock.
 *      Inode wont be chained in superblock s_inodes list
 *      This means :
 *      - fs can't be unmount
 *      - quotas, fsnotify, writeback can't work
 */
struct inode *new_inode_pseudo(struct super_block *sb)
{
        struct inode *inode = alloc_inode(sb);

        if (inode) {
                spin_lock(&inode->i_lock);
                inode->i_state = 0;
                spin_unlock(&inode->i_lock);
        }
        return inode;
}

/**
 *      new_inode       - obtain an inode
 *      @sb: superblock
 *
 *      Allocates a new inode for given superblock. The default gfp_mask
 *      for allocations related to inode->i_mapping is GFP_HIGHUSER_MOVABLE.
 *      If HIGHMEM pages are unsuitable or it is known that pages allocated
 *      for the page cache are not reclaimable or migratable,
 *      mapping_set_gfp_mask() must be called with suitable flags on the
 *      newly created inode's mapping
 *
 */
struct inode *new_inode(struct super_block *sb)
{
        struct inode *inode;

        spin_lock_prefetch(&sb->s_inode_list_lock);

        inode = new_inode_pseudo(sb);
        if (inode)
                inode_sb_list_add(inode);
        return inode;
}
EXPORT_SYMBOL(new_inode);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
void lockdep_annotate_inode_mutex_key(struct inode *inode)
{
        if (S_ISDIR(inode->i_mode)) {
                struct file_system_type *type = inode->i_sb->s_type;

                /* Set new key only if filesystem hasn't already changed it */
                if (lockdep_match_class(&inode->i_rwsem, &type->i_mutex_key)) {
                        /*
                         * ensure nobody is actually holding i_mutex
                         */
                        // mutex_destroy(&inode->i_mutex);
                        init_rwsem(&inode->i_rwsem);
                        lockdep_set_class(&inode->i_rwsem,
                                          &type->i_mutex_dir_key);
                }
        }
}
EXPORT_SYMBOL(lockdep_annotate_inode_mutex_key);
#endif

/**
 * unlock_new_inode - clear the I_NEW state and wake up any waiters
 * @inode:      new inode to unlock
 *
 * Called when the inode is fully initialised to clear the new state of the
 * inode and wake up anyone waiting for the inode to finish initialisation.
 */
void unlock_new_inode(struct inode *inode)
{
        lockdep_annotate_inode_mutex_key(inode);
        spin_lock(&inode->i_lock);
        WARN_ON(!(inode->i_state & I_NEW));
        inode->i_state &= ~I_NEW & ~I_CREATING;
        smp_mb();
        wake_up_bit(&inode->i_state, __I_NEW);
        spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL(unlock_new_inode);

void discard_new_inode(struct inode *inode)
{
        lockdep_annotate_inode_mutex_key(inode);
        spin_lock(&inode->i_lock);
        WARN_ON(!(inode->i_state & I_NEW));
        inode->i_state &= ~I_NEW;
        smp_mb();
        wake_up_bit(&inode->i_state, __I_NEW);
        spin_unlock(&inode->i_lock);
        iput(inode);
}
EXPORT_SYMBOL(discard_new_inode);

/**
 * lock_two_nondirectories - take two i_mutexes on non-directory objects
 *
 * Lock any non-NULL argument that is not a directory.
 * Zero, one or two objects may be locked by this function.
 *
 * @inode1: first inode to lock
 * @inode2: second inode to lock
 */
void lock_two_nondirectories(struct inode *inode1, struct inode *inode2)
{
        if (inode1 > inode2)
                swap(inode1, inode2);

        if (inode1 && !S_ISDIR(inode1->i_mode))
                inode_lock(inode1);
        if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
                inode_lock_nested(inode2, I_MUTEX_NONDIR2);
}
EXPORT_SYMBOL(lock_two_nondirectories);

/**
 * unlock_two_nondirectories - release locks from lock_two_nondirectories()
 * @inode1: first inode to unlock
 * @inode2: second inode to unlock
 */
void unlock_two_nondirectories(struct inode *inode1, struct inode *inode2)
{
        if (inode1 && !S_ISDIR(inode1->i_mode))
                inode_unlock(inode1);
        if (inode2 && !S_ISDIR(inode2->i_mode) && inode2 != inode1)
                inode_unlock(inode2);
}
EXPORT_SYMBOL(unlock_two_nondirectories);

/**
 * inode_insert5 - obtain an inode from a mounted file system
 * @inode:      pre-allocated inode to use for insert to cache
 * @hashval:    hash value (usually inode number) to get
 * @test:       callback used for comparisons between inodes
 * @set:        callback used to initialize a new struct inode
 * @data:       opaque data pointer to pass to @test and @set
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * and if present it is return it with an increased reference count. This is
 * a variant of iget5_locked() for callers that don't want to fail on memory
 * allocation of inode.
 *
 * If the inode is not in cache, insert the pre-allocated inode to cache and
 * return it locked, hashed, and with the I_NEW flag set. The file system gets
 * to fill it in before unlocking it via unlock_new_inode().
 *
 * Note both @test and @set are called with the inode_hash_lock held, so can't
 * sleep.
 */
struct inode *inode_insert5(struct inode *inode, unsigned long hashval,
                            int (*test)(struct inode *, void *),
                            int (*set)(struct inode *, void *), void *data)
{
        struct hlist_head *head = inode_hashtable + hash(inode->i_sb, hashval);
        struct inode *old;

again:
        spin_lock(&inode_hash_lock);
        old = find_inode(inode->i_sb, head, test, data);
        if (unlikely(old)) {
                /*
                 * Uhhuh, somebody else created the same inode under us.
                 * Use the old inode instead of the preallocated one.
                 */
                spin_unlock(&inode_hash_lock);
                if (IS_ERR(old))
                        return NULL;
                wait_on_inode(old);
                if (unlikely(inode_unhashed(old))) {
                        iput(old);
                        goto again;
                }
                return old;
        }

        if (set && unlikely(set(inode, data))) {
                inode = NULL;
                goto unlock;
        }

        /*
         * Return the locked inode with I_NEW set, the
         * caller is responsible for filling in the contents
         */
        spin_lock(&inode->i_lock);
        inode->i_state |= I_NEW;
        hlist_add_head_rcu(&inode->i_hash, head);
        spin_unlock(&inode->i_lock);

        /*
         * Add inode to the sb list if it's not already. It has I_NEW at this
         * point, so it should be safe to test i_sb_list locklessly.
         */
        if (list_empty(&inode->i_sb_list))
                inode_sb_list_add(inode);
unlock:
        spin_unlock(&inode_hash_lock);

        return inode;
}
EXPORT_SYMBOL(inode_insert5);

/**
 * iget5_locked - obtain an inode from a mounted file system
 * @sb:         super block of file system
 * @hashval:    hash value (usually inode number) to get
 * @test:       callback used for comparisons between inodes
 * @set:        callback used to initialize a new struct inode
 * @data:       opaque data pointer to pass to @test and @set
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * and if present it is return it with an increased reference count. This is
 * a generalized version of iget_locked() for file systems where the inode
 * number is not sufficient for unique identification of an inode.
 *
 * If the inode is not in cache, allocate a new inode and return it locked,
 * hashed, and with the I_NEW flag set. The file system gets to fill it in
 * before unlocking it via unlock_new_inode().
 *
 * Note both @test and @set are called with the inode_hash_lock held, so can't
 * sleep.
 */
struct inode *iget5_locked(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *),
                int (*set)(struct inode *, void *), void *data)
{
        struct inode *inode = ilookup5(sb, hashval, test, data);

        if (!inode) {
                struct inode *new = alloc_inode(sb);

                if (new) {
                        new->i_state = 0;
                        inode = inode_insert5(new, hashval, test, set, data);
                        if (unlikely(inode != new))
                                destroy_inode(new);
                }
        }
        return inode;
}
EXPORT_SYMBOL(iget5_locked);

/**
 * iget_locked - obtain an inode from a mounted file system
 * @sb:         super block of file system
 * @ino:        inode number to get
 *
 * Search for the inode specified by @ino in the inode cache and if present
 * return it with an increased reference count. This is for file systems
 * where the inode number is sufficient for unique identification of an inode.
 *
 * If the inode is not in cache, allocate a new inode and return it locked,
 * hashed, and with the I_NEW flag set.  The file system gets to fill it in
 * before unlocking it via unlock_new_inode().
 */
struct inode *iget_locked(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);
        struct inode *inode;
again:
        spin_lock(&inode_hash_lock);
        inode = find_inode_fast(sb, head, ino);
        spin_unlock(&inode_hash_lock);
        if (inode) {
                if (IS_ERR(inode))
                        return NULL;
                wait_on_inode(inode);
                if (unlikely(inode_unhashed(inode))) {
                        iput(inode);
                        goto again;
                }
                return inode;
        }

        inode = alloc_inode(sb);
        if (inode) {
                struct inode *old;

                spin_lock(&inode_hash_lock);
                /* We released the lock, so.. */
                old = find_inode_fast(sb, head, ino);
                if (!old) {
                        inode->i_ino = ino;
                        spin_lock(&inode->i_lock);
                        inode->i_state = I_NEW;
                        hlist_add_head_rcu(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        inode_sb_list_add(inode);
                        spin_unlock(&inode_hash_lock);

                        /* Return the locked inode with I_NEW set, the
                         * caller is responsible for filling in the contents
                         */
                        return inode;
                }

                /*
                 * Uhhuh, somebody else created the same inode under
                 * us. Use the old inode instead of the one we just
                 * allocated.
                 */
                spin_unlock(&inode_hash_lock);
                destroy_inode(inode);
                if (IS_ERR(old))
                        return NULL;
                inode = old;
                wait_on_inode(inode);
                if (unlikely(inode_unhashed(inode))) {
                        iput(inode);
                        goto again;
                }
        }
        return inode;
}
EXPORT_SYMBOL(iget_locked);

/*
 * search the inode cache for a matching inode number.
 * If we find one, then the inode number we are trying to
 * allocate is not unique and so we should not use it.
 *
 * Returns 1 if the inode number is unique, 0 if it is not.
 */
static int test_inode_iunique(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *b = inode_hashtable + hash(sb, ino);
        struct inode *inode;

        hlist_for_each_entry_rcu(inode, b, i_hash) {
                if (inode->i_ino == ino && inode->i_sb == sb)
                        return 0;
        }
        return 1;
}

/**
 *      iunique - get a unique inode number
 *      @sb: superblock
 *      @max_reserved: highest reserved inode number
 *
 *      Obtain an inode number that is unique on the system for a given
 *      superblock. This is used by file systems that have no natural
 *      permanent inode numbering system. An inode number is returned that
 *      is higher than the reserved limit but unique.
 *
 *      BUGS:
 *      With a large number of inodes live on the file system this function
 *      currently becomes quite slow.
 */
ino_t iunique(struct super_block *sb, ino_t max_reserved)
{
        /*
         * On a 32bit, non LFS stat() call, glibc will generate an EOVERFLOW
         * error if st_ino won't fit in target struct field. Use 32bit counter
         * here to attempt to avoid that.
         */
        static DEFINE_SPINLOCK(iunique_lock);
        static unsigned int counter;
        ino_t res;

        rcu_read_lock();
        spin_lock(&iunique_lock);
        do {
                if (counter <= max_reserved)
                        counter = max_reserved + 1;
                res = counter++;
        } while (!test_inode_iunique(sb, res));
        spin_unlock(&iunique_lock);
        rcu_read_unlock();

        return res;
}
EXPORT_SYMBOL(iunique);

struct inode *igrab(struct inode *inode)
{
        spin_lock(&inode->i_lock);
        if (!(inode->i_state & (I_FREEING|I_WILL_FREE))) {
                __iget(inode);
                spin_unlock(&inode->i_lock);
        } else {
                spin_unlock(&inode->i_lock);
                /*
                 * Handle the case where s_op->clear_inode is not been
                 * called yet, and somebody is calling igrab
                 * while the inode is getting freed.
                 */
                inode = NULL;
        }
        return inode;
}
EXPORT_SYMBOL(igrab);

/**
 * ilookup5_nowait - search for an inode in the inode cache
 * @sb:         super block of file system to search
 * @hashval:    hash value (usually inode number) to search for
 * @test:       callback used for comparisons between inodes
 * @data:       opaque data pointer to pass to @test
 *
 * Search for the inode specified by @hashval and @data in the inode cache.
 * If the inode is in the cache, the inode is returned with an incremented
 * reference count.
 *
 * Note: I_NEW is not waited upon so you have to be very careful what you do
 * with the returned inode.  You probably should be using ilookup5() instead.
 *
 * Note2: @test is called with the inode_hash_lock held, so can't sleep.
 */
struct inode *ilookup5_nowait(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);
        struct inode *inode;

        spin_lock(&inode_hash_lock);
        inode = find_inode(sb, head, test, data);
        spin_unlock(&inode_hash_lock);

        return IS_ERR(inode) ? NULL : inode;
}
EXPORT_SYMBOL(ilookup5_nowait);

/**
 * ilookup5 - search for an inode in the inode cache
 * @sb:         super block of file system to search
 * @hashval:    hash value (usually inode number) to search for
 * @test:       callback used for comparisons between inodes
 * @data:       opaque data pointer to pass to @test
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * and if the inode is in the cache, return the inode with an incremented
 * reference count.  Waits on I_NEW before returning the inode.
 * returned with an incremented reference count.
 *
 * This is a generalized version of ilookup() for file systems where the
 * inode number is not sufficient for unique identification of an inode.
 *
 * Note: @test is called with the inode_hash_lock held, so can't sleep.
 */
struct inode *ilookup5(struct super_block *sb, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct inode *inode;
again:
        inode = ilookup5_nowait(sb, hashval, test, data);
        if (inode) {
                wait_on_inode(inode);
                if (unlikely(inode_unhashed(inode))) {
                        iput(inode);
                        goto again;
                }
        }
        return inode;
}
EXPORT_SYMBOL(ilookup5);

/**
 * ilookup - search for an inode in the inode cache
 * @sb:         super block of file system to search
 * @ino:        inode number to search for
 *
 * Search for the inode @ino in the inode cache, and if the inode is in the
 * cache, the inode is returned with an incremented reference count.
 */
struct inode *ilookup(struct super_block *sb, unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);
        struct inode *inode;
again:
        spin_lock(&inode_hash_lock);
        inode = find_inode_fast(sb, head, ino);
        spin_unlock(&inode_hash_lock);

        if (inode) {
                if (IS_ERR(inode))
                        return NULL;
                wait_on_inode(inode);
                if (unlikely(inode_unhashed(inode))) {
                        iput(inode);
                        goto again;
                }
        }
        return inode;
}
EXPORT_SYMBOL(ilookup);

/**
 * find_inode_nowait - find an inode in the inode cache
 * @sb:         super block of file system to search
 * @hashval:    hash value (usually inode number) to search for
 * @match:      callback used for comparisons between inodes
 * @data:       opaque data pointer to pass to @match
 *
 * Search for the inode specified by @hashval and @data in the inode
 * cache, where the helper function @match will return 0 if the inode
 * does not match, 1 if the inode does match, and -1 if the search
 * should be stopped.  The @match function must be responsible for
 * taking the i_lock spin_lock and checking i_state for an inode being
 * freed or being initialized, and incrementing the reference count
 * before returning 1.  It also must not sleep, since it is called with
 * the inode_hash_lock spinlock held.
 *
 * This is a even more generalized version of ilookup5() when the
 * function must never block --- find_inode() can block in
 * __wait_on_freeing_inode() --- or when the caller can not increment
 * the reference count because the resulting iput() might cause an
 * inode eviction.  The tradeoff is that the @match funtion must be
 * very carefully implemented.
 */
struct inode *find_inode_nowait(struct super_block *sb,
                                unsigned long hashval,
                                int (*match)(struct inode *, unsigned long,
                                             void *),
                                void *data)
{
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);
        struct inode *inode, *ret_inode = NULL;
        int mval;

        spin_lock(&inode_hash_lock);
        hlist_for_each_entry(inode, head, i_hash) {
                if (inode->i_sb != sb)
                        continue;
                mval = match(inode, hashval, data);
                if (mval == 0)
                        continue;
                if (mval == 1)
                        ret_inode = inode;
                goto out;
        }
out:
        spin_unlock(&inode_hash_lock);
        return ret_inode;
}
EXPORT_SYMBOL(find_inode_nowait);

/**
 * find_inode_rcu - find an inode in the inode cache
 * @sb:         Super block of file system to search
 * @hashval:    Key to hash
 * @test:       Function to test match on an inode
 * @data:       Data for test function
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * where the helper function @test will return 0 if the inode does not match
 * and 1 if it does.  The @test function must be responsible for taking the
 * i_lock spin_lock and checking i_state for an inode being freed or being
 * initialized.
 *
 * If successful, this will return the inode for which the @test function
 * returned 1 and NULL otherwise.
 *
 * The @test function is not permitted to take a ref on any inode presented.
 * It is also not permitted to sleep.
 *
 * The caller must hold the RCU read lock.
 */
struct inode *find_inode_rcu(struct super_block *sb, unsigned long hashval,
                             int (*test)(struct inode *, void *), void *data)
{
        struct hlist_head *head = inode_hashtable + hash(sb, hashval);
        struct inode *inode;

        RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
                         "suspicious find_inode_rcu() usage");

        hlist_for_each_entry_rcu(inode, head, i_hash) {
                if (inode->i_sb == sb &&
                    !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)) &&
                    test(inode, data))
                        return inode;
        }
        return NULL;
}
EXPORT_SYMBOL(find_inode_rcu);

/**
 * find_inode_by_ino_rcu - Find an inode in the inode cache
 * @sb:         Super block of file system to search
 * @ino:        The inode number to match
 *
 * Search for the inode specified by @hashval and @data in the inode cache,
 * where the helper function @test will return 0 if the inode does not match
 * and 1 if it does.  The @test function must be responsible for taking the
 * i_lock spin_lock and checking i_state for an inode being freed or being
 * initialized.
 *
 * If successful, this will return the inode for which the @test function
 * returned 1 and NULL otherwise.
 *
 * The @test function is not permitted to take a ref on any inode presented.
 * It is also not permitted to sleep.
 *
 * The caller must hold the RCU read lock.
 */
struct inode *find_inode_by_ino_rcu(struct super_block *sb,
                                    unsigned long ino)
{
        struct hlist_head *head = inode_hashtable + hash(sb, ino);
        struct inode *inode;

        RCU_LOCKDEP_WARN(!rcu_read_lock_held(),
                         "suspicious find_inode_by_ino_rcu() usage");

        hlist_for_each_entry_rcu(inode, head, i_hash) {
                if (inode->i_ino == ino &&
                    inode->i_sb == sb &&
                    !(READ_ONCE(inode->i_state) & (I_FREEING | I_WILL_FREE)))
                    return inode;
        }
        return NULL;
}
EXPORT_SYMBOL(find_inode_by_ino_rcu);

int insert_inode_locked(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        ino_t ino = inode->i_ino;
        struct hlist_head *head = inode_hashtable + hash(sb, ino);

        while (1) {
                struct inode *old = NULL;
                spin_lock(&inode_hash_lock);
                hlist_for_each_entry(old, head, i_hash) {
                        if (old->i_ino != ino)
                                continue;
                        if (old->i_sb != sb)
                                continue;
                        spin_lock(&old->i_lock);
                        if (old->i_state & (I_FREEING|I_WILL_FREE)) {
                                spin_unlock(&old->i_lock);
                                continue;
                        }
                        break;
                }
                if (likely(!old)) {
                        spin_lock(&inode->i_lock);
                        inode->i_state |= I_NEW | I_CREATING;
                        hlist_add_head_rcu(&inode->i_hash, head);
                        spin_unlock(&inode->i_lock);
                        spin_unlock(&inode_hash_lock);
                        return 0;
                }
                if (unlikely(old->i_state & I_CREATING)) {
                        spin_unlock(&old->i_lock);
                        spin_unlock(&inode_hash_lock);
                        return -EBUSY;
                }
                __iget(old);
                spin_unlock(&old->i_lock);
                spin_unlock(&inode_hash_lock);
                wait_on_inode(old);
                if (unlikely(!inode_unhashed(old))) {
                        iput(old);
                        return -EBUSY;
                }
                iput(old);
        }
}
EXPORT_SYMBOL(insert_inode_locked);

int insert_inode_locked4(struct inode *inode, unsigned long hashval,
                int (*test)(struct inode *, void *), void *data)
{
        struct inode *old;

        inode->i_state |= I_CREATING;
        old = inode_insert5(inode, hashval, test, NULL, data);

        if (old != inode) {
                iput(old);
                return -EBUSY;
        }
        return 0;
}
EXPORT_SYMBOL(insert_inode_locked4);


int generic_delete_inode(struct inode *inode)
{
        return 1;
}
EXPORT_SYMBOL(generic_delete_inode);

/*
 * Called when we're dropping the last reference
 * to an inode.
 *
 * Call the FS "drop_inode()" function, defaulting to
 * the legacy UNIX filesystem behaviour.  If it tells
 * us to evict inode, do so.  Otherwise, retain inode
 * in cache if fs is alive, sync and evict if fs is
 * shutting down.
 */
static void iput_final(struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        const struct super_operations *op = inode->i_sb->s_op;
        unsigned long state;
        int drop;

        WARN_ON(inode->i_state & I_NEW);

        if (op->drop_inode)
                drop = op->drop_inode(inode);
        else
                drop = generic_drop_inode(inode);

        if (!drop &&
            !(inode->i_state & I_DONTCACHE) &&
            (sb->s_flags & SB_ACTIVE)) {
                __inode_add_lru(inode, true);
                spin_unlock(&inode->i_lock);
                return;
        }

        state = inode->i_state;
        if (!drop) {
                WRITE_ONCE(inode->i_state, state | I_WILL_FREE);
                spin_unlock(&inode->i_lock);

                write_inode_now(inode, 1);

                spin_lock(&inode->i_lock);
                state = inode->i_state;
                WARN_ON(state & I_NEW);
                state &= ~I_WILL_FREE;
        }

        WRITE_ONCE(inode->i_state, state | I_FREEING);
        if (!list_empty(&inode->i_lru))
                inode_lru_list_del(inode);
        spin_unlock(&inode->i_lock);

        evict(inode);
}

/**
 *      iput    - put an inode
 *      @inode: inode to put
 *
 *      Puts an inode, dropping its usage count. If the inode use count hits
 *      zero, the inode is then freed and may also be destroyed.
 *
 *      Consequently, iput() can sleep.
 */
void iput(struct inode *inode)
{
        if (!inode)
                return;
        BUG_ON(inode->i_state & I_CLEAR);
retry:
        if (atomic_dec_and_lock(&inode->i_count, &inode->i_lock)) {
                if (inode->i_nlink && (inode->i_state & I_DIRTY_TIME)) {
                        atomic_inc(&inode->i_count);
                        spin_unlock(&inode->i_lock);
                        trace_writeback_lazytime_iput(inode);
                        mark_inode_dirty_sync(inode);
                        goto retry;
                }
                iput_final(inode);
        }
}
EXPORT_SYMBOL(iput);

#ifdef CONFIG_BLOCK
/**
 *      bmap    - find a block number in a file
 *      @inode:  inode owning the block number being requested
 *      @block: pointer containing the block to find
 *
 *      Replaces the value in ``*block`` with the block number on the device holding
 *      corresponding to the requested block number in the file.
 *      That is, asked for block 4 of inode 1 the function will replace the
 *      4 in ``*block``, with disk block relative to the disk start that holds that
 *      block of the file.
 *
 *      Returns -EINVAL in case of error, 0 otherwise. If mapping falls into a
 *      hole, returns 0 and ``*block`` is also set to 0.
 */
int bmap(struct inode *inode, sector_t *block)
{
        if (!inode->i_mapping->a_ops->bmap)
                return -EINVAL;

        *block = inode->i_mapping->a_ops->bmap(inode->i_mapping, *block);
        return 0;
}
EXPORT_SYMBOL(bmap);
#endif

/*
 * With relative atime, only update atime if the previous atime is
 * earlier than either the ctime or mtime or if at least a day has
 * passed since the last atime update.
 */
static int relatime_need_update(struct vfsmount *mnt, struct inode *inode,
                             struct timespec64 now)
{

        if (!(mnt->mnt_flags & MNT_RELATIME))
                return 1;
        /*
         * Is mtime younger than atime? If yes, update atime:
         */
        if (timespec64_compare(&inode->i_mtime, &inode->i_atime) >= 0)
                return 1;
        /*
         * Is ctime younger than atime? If yes, update atime:
         */
        if (timespec64_compare(&inode->i_ctime, &inode->i_atime) >= 0)
                return 1;

        /*
         * Is the previous atime value older than a day? If yes,
         * update atime:
         */
        if ((long)(now.tv_sec - inode->i_atime.tv_sec) >= 24*60*60)
                return 1;
        /*
         * Good, we can skip the atime update:
         */
        return 0;
}

int generic_update_time(struct inode *inode, struct timespec64 *time, int flags)
{
        int dirty_flags = 0;

        if (flags & (S_ATIME | S_CTIME | S_MTIME)) {
                if (flags & S_ATIME)
                        inode->i_atime = *time;
                if (flags & S_CTIME)
                        inode->i_ctime = *time;
                if (flags & S_MTIME)
                        inode->i_mtime = *time;

                if (inode->i_sb->s_flags & SB_LAZYTIME)
                        dirty_flags |= I_DIRTY_TIME;
                else
                        dirty_flags |= I_DIRTY_SYNC;
        }

        if ((flags & S_VERSION) && inode_maybe_inc_iversion(inode, false))
                dirty_flags |= I_DIRTY_SYNC;

        __mark_inode_dirty(inode, dirty_flags);
        return 0;
}
EXPORT_SYMBOL(generic_update_time);

/*
 * This does the actual work of updating an inodes time or version.  Must have
 * had called mnt_want_write() before calling this.
 */
int inode_update_time(struct inode *inode, struct timespec64 *time, int flags)
{
        if (inode->i_op->update_time)
                return inode->i_op->update_time(inode, time, flags);
        return generic_update_time(inode, time, flags);
}
EXPORT_SYMBOL(inode_update_time);

/**
 *      atime_needs_update      -       update the access time
 *      @path: the &struct path to update
 *      @inode: inode to update
 *
 *      Update the accessed time on an inode and mark it for writeback.
 *      This function automatically handles read only file systems and media,
 *      as well as the "noatime" flag and inode specific "noatime" markers.
 */
bool atime_needs_update(const struct path *path, struct inode *inode)
{
        struct vfsmount *mnt = path->mnt;
        struct timespec64 now;

        if (inode->i_flags & S_NOATIME)
                return false;

        /* Atime updates will likely cause i_uid and i_gid to be written
         * back improprely if their true value is unknown to the vfs.
         */
        if (HAS_UNMAPPED_ID(mnt_user_ns(mnt), inode))
                return false;

        if (IS_NOATIME(inode))
                return false;
        if ((inode->i_sb->s_flags & SB_NODIRATIME) && S_ISDIR(inode->i_mode))
                return false;

        if (mnt->mnt_flags & MNT_NOATIME)
                return false;
        if ((mnt->mnt_flags & MNT_NODIRATIME) && S_ISDIR(inode->i_mode))
                return false;

        now = current_time(inode);

        if (!relatime_need_update(mnt, inode, now))
                return false;

        if (timespec64_equal(&inode->i_atime, &now))
                return false;

        return true;
}

void touch_atime(const struct path *path)
{
        struct vfsmount *mnt = path->mnt;
        struct inode *inode = d_inode(path->dentry);
        struct timespec64 now;

        if (!atime_needs_update(path, inode))
                return;

        if (!sb_start_write_trylock(inode->i_sb))
                return;

        if (__mnt_want_write(mnt) != 0)
                goto skip_update;
        /*
         * File systems can error out when updating inodes if they need to
         * allocate new space to modify an inode (such is the case for
         * Btrfs), but since we touch atime while walking down the path we
         * really don't care if we failed to update the atime of the file,
         * so just ignore the return value.
         * We may also fail on filesystems that have the ability to make parts
         * of the fs read only, e.g. subvolumes in Btrfs.
         */
        now = current_time(inode);
        inode_update_time(inode, &now, S_ATIME);
        __mnt_drop_write(mnt);
skip_update:
        sb_end_write(inode->i_sb);
}
EXPORT_SYMBOL(touch_atime);

/*
 * The logic we want is
 *
 *      if suid or (sgid and xgrp)
 *              remove privs
 */
int should_remove_suid(struct dentry *dentry)
{
        umode_t mode = d_inode(dentry)->i_mode;
        int kill = 0;

        /* suid always must be killed */
        if (unlikely(mode & S_ISUID))
                kill = ATTR_KILL_SUID;

        /*
         * sgid without any exec bits is just a mandatory locking mark; leave
         * it alone.  If some exec bits are set, it's a real sgid; kill it.
         */
        if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
                kill |= ATTR_KILL_SGID;

        if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
                return kill;

        return 0;
}
EXPORT_SYMBOL(should_remove_suid);

/*
 * Return mask of changes for notify_change() that need to be done as a
 * response to write or truncate. Return 0 if nothing has to be changed.
 * Negative value on error (change should be denied).
 */
int dentry_needs_remove_privs(struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        int mask = 0;
        int ret;

        if (IS_NOSEC(inode))
                return 0;

        mask = should_remove_suid(dentry);
        ret = security_inode_need_killpriv(dentry);
        if (ret < 0)
                return ret;
        if (ret)
                mask |= ATTR_KILL_PRIV;
        return mask;
}

static int __remove_privs(struct user_namespace *mnt_userns,
                          struct dentry *dentry, int kill)
{
        struct iattr newattrs;

        newattrs.ia_valid = ATTR_FORCE | kill;
        /*
         * Note we call this on write, so notify_change will not
         * encounter any conflicting delegations:
         */
        return notify_change(mnt_userns, dentry, &newattrs, NULL);
}

static int __file_remove_privs(struct file *file, unsigned int flags)
{
        struct dentry *dentry = file_dentry(file);
        struct inode *inode = file_inode(file);
        int error = 0;
        int kill;

        if (IS_NOSEC(inode) || !S_ISREG(inode->i_mode))
                return 0;

        kill = dentry_needs_remove_privs(dentry);
        if (kill < 0)
                return kill;

        if (kill) {
                if (flags & IOCB_NOWAIT)
                        return -EAGAIN;

                error = __remove_privs(file_mnt_user_ns(file), dentry, kill);
        }

        if (!error)
                inode_has_no_xattr(inode);
        return error;
}

/**
 * file_remove_privs - remove special file privileges (suid, capabilities)
 * @file: file to remove privileges from
 *
 * When file is modified by a write or truncation ensure that special
 * file privileges are removed.
 *
 * Return: 0 on success, negative errno on failure.
 */
int file_remove_privs(struct file *file)
{
        return __file_remove_privs(file, 0);
}
EXPORT_SYMBOL(file_remove_privs);

static int inode_needs_update_time(struct inode *inode, struct timespec64 *now)
{
        int sync_it = 0;

        /* First try to exhaust all avenues to not sync */
        if (IS_NOCMTIME(inode))
                return 0;

        if (!timespec64_equal(&inode->i_mtime, now))
                sync_it = S_MTIME;

        if (!timespec64_equal(&inode->i_ctime, now))
                sync_it |= S_CTIME;

        if (IS_I_VERSION(inode) && inode_iversion_need_inc(inode))
                sync_it |= S_VERSION;

        if (!sync_it)
                return 0;

        return sync_it;
}

static int __file_update_time(struct file *file, struct timespec64 *now,
                        int sync_mode)
{
        int ret = 0;
        struct inode *inode = file_inode(file);

        /* try to update time settings */
        if (!__mnt_want_write_file(file)) {
                ret = inode_update_time(inode, now, sync_mode);
                __mnt_drop_write_file(file);
        }

        return ret;
}

/**
 * file_update_time - update mtime and ctime time
 * @file: file accessed
 *
 * Update the mtime and ctime members of an inode and mark the inode for
 * writeback. Note that this function is meant exclusively for usage in
 * the file write path of filesystems, and filesystems may choose to
 * explicitly ignore updates via this function with the _NOCMTIME inode
 * flag, e.g. for network filesystem where these imestamps are handled
 * by the server. This can return an error for file systems who need to
 * allocate space in order to update an inode.
 *
 * Return: 0 on success, negative errno on failure.
 */
int file_update_time(struct file *file)
{
        int ret;
        struct inode *inode = file_inode(file);
        struct timespec64 now = current_time(inode);

        ret = inode_needs_update_time(inode, &now);
        if (ret <= 0)
                return ret;

        return __file_update_time(file, &now, ret);
}
EXPORT_SYMBOL(file_update_time);

/**
 * file_modified_flags - handle mandated vfs changes when modifying a file
 * @file: file that was modified
 * @flags: kiocb flags
 *
 * When file has been modified ensure that special
 * file privileges are removed and time settings are updated.
 *
 * If IOCB_NOWAIT is set, special file privileges will not be removed and
 * time settings will not be updated. It will return -EAGAIN.
 *
 * Context: Caller must hold the file's inode lock.
 *
 * Return: 0 on success, negative errno on failure.
 */
static int file_modified_flags(struct file *file, int flags)
{
        int ret;
        struct inode *inode = file_inode(file);
        struct timespec64 now = current_time(inode);

        /*
         * Clear the security bits if the process is not being run by root.
         * This keeps people from modifying setuid and setgid binaries.
         */
        ret = __file_remove_privs(file, flags);
        if (ret)
                return ret;

        if (unlikely(file->f_mode & FMODE_NOCMTIME))
                return 0;

        ret = inode_needs_update_time(inode, &now);
        if (ret <= 0)
                return ret;
        if (flags & IOCB_NOWAIT)
                return -EAGAIN;

        return __file_update_time(file, &now, ret);
}

/**
 * file_modified - handle mandated vfs changes when modifying a file
 * @file: file that was modified
 *
 * When file has been modified ensure that special
 * file privileges are removed and time settings are updated.
 *
 * Context: Caller must hold the file's inode lock.
 *
 * Return: 0 on success, negative errno on failure.
 */
int file_modified(struct file *file)
{
        return file_modified_flags(file, 0);
}
EXPORT_SYMBOL(file_modified);

/**
 * kiocb_modified - handle mandated vfs changes when modifying a file
 * @iocb: iocb that was modified
 *
 * When file has been modified ensure that special
 * file privileges are removed and time settings are updated.
 *
 * Context: Caller must hold the file's inode lock.
 *
 * Return: 0 on success, negative errno on failure.
 */
int kiocb_modified(struct kiocb *iocb)
{
        return file_modified_flags(iocb->ki_filp, iocb->ki_flags);
}
EXPORT_SYMBOL_GPL(kiocb_modified);

int inode_needs_sync(struct inode *inode)
{
        if (IS_SYNC(inode))
                return 1;
        if (S_ISDIR(inode->i_mode) && IS_DIRSYNC(inode))
                return 1;
        return 0;
}
EXPORT_SYMBOL(inode_needs_sync);

/*
 * If we try to find an inode in the inode hash while it is being
 * deleted, we have to wait until the filesystem completes its
 * deletion before reporting that it isn't found.  This function waits
 * until the deletion _might_ have completed.  Callers are responsible
 * to recheck inode state.
 *
 * It doesn't matter if I_NEW is not set initially, a call to
 * wake_up_bit(&inode->i_state, __I_NEW) after removing from the hash list
 * will DTRT.
 */
static void __wait_on_freeing_inode(struct inode *inode)
{
        wait_queue_head_t *wq;
        DEFINE_WAIT_BIT(wait, &inode->i_state, __I_NEW);
        wq = bit_waitqueue(&inode->i_state, __I_NEW);
        prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
        spin_unlock(&inode->i_lock);
        spin_unlock(&inode_hash_lock);
        schedule();
        finish_wait(wq, &wait.wq_entry);
        spin_lock(&inode_hash_lock);
}

static __initdata unsigned long ihash_entries;
static int __init set_ihash_entries(char *str)
{
        if (!str)
                return 0;
        ihash_entries = simple_strtoul(str, &str, 0);
        return 1;
}
__setup("ihash_entries=", set_ihash_entries);

/*
 * Initialize the waitqueues and inode hash table.
 */
void __init inode_init_early(void)
{
        /* If hashes are distributed across NUMA nodes, defer
         * hash allocation until vmalloc space is available.
         */
        if (hashdist)
                return;

        inode_hashtable =
                alloc_large_system_hash("Inode-cache",
                                        sizeof(struct hlist_head),
                                        ihash_entries,
                                        14,
                                        HASH_EARLY | HASH_ZERO,
                                        &i_hash_shift,
                                        &i_hash_mask,
                                        0,
                                        0);
}

void __init inode_init(void)
{
        /* inode slab cache */
        inode_cachep = kmem_cache_create("inode_cache",
                                         sizeof(struct inode),
                                         0,
                                         (SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
                                         SLAB_MEM_SPREAD|SLAB_ACCOUNT),
                                         init_once);

        /* Hash may have been set up in inode_init_early */
        if (!hashdist)
                return;

        inode_hashtable =
                alloc_large_system_hash("Inode-cache",
                                        sizeof(struct hlist_head),
                                        ihash_entries,
                                        14,
                                        HASH_ZERO,
                                        &i_hash_shift,
                                        &i_hash_mask,
                                        0,
                                        0);
}

void init_special_inode(struct inode *inode, umode_t mode, dev_t rdev)
{
        inode->i_mode = mode;
        if (S_ISCHR(mode)) {
                inode->i_fop = &def_chr_fops;
                inode->i_rdev = rdev;
        } else if (S_ISBLK(mode)) {
                inode->i_fop = &def_blk_fops;
                inode->i_rdev = rdev;
        } else if (S_ISFIFO(mode))
                inode->i_fop = &pipefifo_fops;
        else if (S_ISSOCK(mode))
                ;       /* leave it no_open_fops */
        else
                printk(KERN_DEBUG "init_special_inode: bogus i_mode (%o) for"
                                  " inode %s:%lu\n", mode, inode->i_sb->s_id,
                                  inode->i_ino);
}
EXPORT_SYMBOL(init_special_inode);

/**
 * inode_init_owner - Init uid,gid,mode for new inode according to posix standards
 * @mnt_userns: User namespace of the mount the inode was created from
 * @inode: New inode
 * @dir: Directory inode
 * @mode: mode of the new inode
 *
 * If the inode has been created through an idmapped mount the user namespace of
 * the vfsmount must be passed through @mnt_userns. This function will then take
 * care to map the inode according to @mnt_userns before checking permissions
 * and initializing i_uid and i_gid. On non-idmapped mounts or if permission
 * checking is to be performed on the raw inode simply passs init_user_ns.
 */
void inode_init_owner(struct user_namespace *mnt_userns, struct inode *inode,
                      const struct inode *dir, umode_t mode)
{
        inode_fsuid_set(inode, mnt_userns);
        if (dir && dir->i_mode & S_ISGID) {
                inode->i_gid = dir->i_gid;

                /* Directories are special, and always inherit S_ISGID */
                if (S_ISDIR(mode))
                        mode |= S_ISGID;
        } else
                inode_fsgid_set(inode, mnt_userns);
        inode->i_mode = mode;
}
EXPORT_SYMBOL(inode_init_owner);

/**
 * inode_owner_or_capable - check current task permissions to inode
 * @mnt_userns: user namespace of the mount the inode was found from
 * @inode: inode being checked
 *
 * Return true if current either has CAP_FOWNER in a namespace with the
 * inode owner uid mapped, or owns the file.
 *
 * If the inode has been found through an idmapped mount the user namespace of
 * the vfsmount must be passed through @mnt_userns. This function will then take
 * care to map the inode according to @mnt_userns before checking permissions.
 * On non-idmapped mounts or if permission checking is to be performed on the
 * raw inode simply passs init_user_ns.
 */
bool inode_owner_or_capable(struct user_namespace *mnt_userns,
                            const struct inode *inode)
{
        kuid_t i_uid;
        struct user_namespace *ns;

        i_uid = i_uid_into_mnt(mnt_userns, inode);
        if (uid_eq(current_fsuid(), i_uid))
                return true;

        ns = current_user_ns();
        if (kuid_has_mapping(ns, i_uid) && ns_capable(ns, CAP_FOWNER))
                return true;
        return false;
}
EXPORT_SYMBOL(inode_owner_or_capable);

/*
 * Direct i/o helper functions
 */
static void __inode_dio_wait(struct inode *inode)
{
        wait_queue_head_t *wq = bit_waitqueue(&inode->i_state, __I_DIO_WAKEUP);
        DEFINE_WAIT_BIT(q, &inode->i_state, __I_DIO_WAKEUP);

        do {
                prepare_to_wait(wq, &q.wq_entry, TASK_UNINTERRUPTIBLE);
                if (atomic_read(&inode->i_dio_count))
                        schedule();
        } while (atomic_read(&inode->i_dio_count));
        finish_wait(wq, &q.wq_entry);
}

/**
 * inode_dio_wait - wait for outstanding DIO requests to finish
 * @inode: inode to wait for
 *
 * Waits for all pending direct I/O requests to finish so that we can
 * proceed with a truncate or equivalent operation.
 *
 * Must be called under a lock that serializes taking new references
 * to i_dio_count, usually by inode->i_mutex.
 */
void inode_dio_wait(struct inode *inode)
{
        if (atomic_read(&inode->i_dio_count))
                __inode_dio_wait(inode);
}
EXPORT_SYMBOL(inode_dio_wait);

/*
 * inode_set_flags - atomically set some inode flags
 *
 * Note: the caller should be holding i_mutex, or else be sure that
 * they have exclusive access to the inode structure (i.e., while the
 * inode is being instantiated).  The reason for the cmpxchg() loop
 * --- which wouldn't be necessary if all code paths which modify
 * i_flags actually followed this rule, is that there is at least one
 * code path which doesn't today so we use cmpxchg() out of an abundance
 * of caution.
 *
 * In the long run, i_mutex is overkill, and we should probably look
 * at using the i_lock spinlock to protect i_flags, and then make sure
 * it is so documented in include/linux/fs.h and that all code follows
 * the locking convention!!
 */
void inode_set_flags(struct inode *inode, unsigned int flags,
                     unsigned int mask)
{
        WARN_ON_ONCE(flags & ~mask);
        set_mask_bits(&inode->i_flags, mask, flags);
}
EXPORT_SYMBOL(inode_set_flags);

void inode_nohighmem(struct inode *inode)
{
        mapping_set_gfp_mask(inode->i_mapping, GFP_USER);
}
EXPORT_SYMBOL(inode_nohighmem);

/**
 * timestamp_truncate - Truncate timespec to a granularity
 * @t: Timespec
 * @inode: inode being updated
 *
 * Truncate a timespec to the granularity supported by the fs
 * containing the inode. Always rounds down. gran must
 * not be 0 nor greater than a second (NSEC_PER_SEC, or 10^9 ns).
 */
struct timespec64 timestamp_truncate(struct timespec64 t, struct inode *inode)
{
        struct super_block *sb = inode->i_sb;
        unsigned int gran = sb->s_time_gran;

        t.tv_sec = clamp(t.tv_sec, sb->s_time_min, sb->s_time_max);
        if (unlikely(t.tv_sec == sb->s_time_max || t.tv_sec == sb->s_time_min))
                t.tv_nsec = 0;

        /* Avoid division in the common cases 1 ns and 1 s. */
        if (gran == 1)
                ; /* nothing */
        else if (gran == NSEC_PER_SEC)
                t.tv_nsec = 0;
        else if (gran > 1 && gran < NSEC_PER_SEC)
                t.tv_nsec -= t.tv_nsec % gran;
        else
                WARN(1, "invalid file time granularity: %u", gran);
        return t;
}
EXPORT_SYMBOL(timestamp_truncate);

/**
 * current_time - Return FS time
 * @inode: inode.
 *
 * Return the current time truncated to the time granularity supported by
 * the fs.
 *
 * Note that inode and inode->sb cannot be NULL.
 * Otherwise, the function warns and returns time without truncation.
 */
struct timespec64 current_time(struct inode *inode)
{
        struct timespec64 now;

        ktime_get_coarse_real_ts64(&now);

        if (unlikely(!inode->i_sb)) {
                WARN(1, "current_time() called with uninitialized super_block in the inode");
                return now;
        }

        return timestamp_truncate(now, inode);
}
EXPORT_SYMBOL(current_time);

/**
 * mode_strip_sgid - handle the sgid bit for non-directories
 * @mnt_userns: User namespace of the mount the inode was created from
 * @dir: parent directory inode
 * @mode: mode of the file to be created in @dir
 *
 * If the @mode of the new file has both the S_ISGID and S_IXGRP bit
 * raised and @dir has the S_ISGID bit raised ensure that the caller is
 * either in the group of the parent directory or they have CAP_FSETID
 * in their user namespace and are privileged over the parent directory.
 * In all other cases, strip the S_ISGID bit from @mode.
 *
 * Return: the new mode to use for the file
 */
umode_t mode_strip_sgid(struct user_namespace *mnt_userns,
                        const struct inode *dir, umode_t mode)
{
        if ((mode & (S_ISGID | S_IXGRP)) != (S_ISGID | S_IXGRP))
                return mode;
        if (S_ISDIR(mode) || !dir || !(dir->i_mode & S_ISGID))
                return mode;
        if (in_group_p(i_gid_into_mnt(mnt_userns, dir)))
                return mode;
        if (capable_wrt_inode_uidgid(mnt_userns, dir, CAP_FSETID))
                return mode;

        return mode & ~S_ISGID;
}
EXPORT_SYMBOL(mode_strip_sgid);