/*
- * fs/eventpoll.c ( Efficent event polling implementation )
- * Copyright (C) 2001,...,2006 Davide Libenzi
+ * fs/eventpoll.c (Efficent event polling implementation)
+ * Copyright (C) 2001,...,2007 Davide Libenzi
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
#include <linux/hash.h>
#include <linux/spinlock.h>
#include <linux/syscalls.h>
-#include <linux/rwsem.h>
#include <linux/rbtree.h>
#include <linux/wait.h>
#include <linux/eventpoll.h>
#include <asm/io.h>
#include <asm/mman.h>
#include <asm/atomic.h>
-#include <asm/semaphore.h>
/*
* LOCKING:
* There are three level of locking required by epoll :
*
* 1) epmutex (mutex)
- * 2) ep->sem (rw_semaphore)
- * 3) ep->lock (rw_lock)
+ * 2) ep->mtx (mutex)
+ * 3) ep->lock (spinlock)
*
* The acquire order is the one listed above, from 1 to 3.
* We need a spinlock (ep->lock) because we manipulate objects
* a spinlock. During the event transfer loop (from kernel to
* user space) we could end up sleeping due a copy_to_user(), so
* we need a lock that will allow us to sleep. This lock is a
- * read-write semaphore (ep->sem). It is acquired on read during
- * the event transfer loop and in write during epoll_ctl(EPOLL_CTL_DEL)
- * and during eventpoll_release_file(). Then we also need a global
- * semaphore to serialize eventpoll_release_file() and ep_free().
- * This semaphore is acquired by ep_free() during the epoll file
+ * mutex (ep->mtx). It is acquired during the event transfer loop,
+ * during epoll_ctl(EPOLL_CTL_DEL) and during eventpoll_release_file().
+ * Then we also need a global mutex to serialize eventpoll_release_file()
+ * and ep_free().
+ * This mutex is acquired by ep_free() during the epoll file
* cleanup path and it is also acquired by eventpoll_release_file()
* if a file has been pushed inside an epoll set and it is then
* close()d without a previous call toepoll_ctl(EPOLL_CTL_DEL).
- * It is possible to drop the "ep->sem" and to use the global
- * semaphore "epmutex" (together with "ep->lock") to have it working,
- * but having "ep->sem" will make the interface more scalable.
+ * It is possible to drop the "ep->mtx" and to use the global
+ * mutex "epmutex" (together with "ep->lock") to have it working,
+ * but having "ep->mtx" will make the interface more scalable.
* Events that require holding "epmutex" are very rare, while for
- * normal operations the epoll private "ep->sem" will guarantee
- * a greater scalability.
+ * normal operations the epoll private "ep->mtx" will guarantee
+ * a better scalability.
*/
#define DEBUG_EPOLL 0
#define EP_MAX_EVENTS (INT_MAX / sizeof(struct epoll_event))
+#define EP_UNACTIVE_PTR ((void *) -1L)
+
struct epoll_filefd {
struct file *file;
int fd;
* Node that is linked into the "wake_task_list" member of the "struct poll_safewake".
* It is used to keep track on all tasks that are currently inside the wake_up() code
* to 1) short-circuit the one coming from the same task and same wait queue head
- * ( loop ) 2) allow a maximum number of epoll descriptors inclusion nesting
+ * (loop) 2) allow a maximum number of epoll descriptors inclusion nesting
* 3) let go the ones coming from other tasks.
*/
struct wake_task_node {
spinlock_t lock;
};
+/*
+ * Each file descriptor added to the eventpoll interface will
+ * have an entry of this type linked to the "rbr" RB tree.
+ */
+struct epitem {
+ /* RB tree node used to link this structure to the eventpoll RB tree */
+ struct rb_node rbn;
+
+ /* List header used to link this structure to the eventpoll ready list */
+ struct list_head rdllink;
+
+ /*
+ * Works together "struct eventpoll"->ovflist in keeping the
+ * single linked chain of items.
+ */
+ struct epitem *next;
+
+ /* The file descriptor information this item refers to */
+ struct epoll_filefd ffd;
+
+ /* Number of active wait queue attached to poll operations */
+ int nwait;
+
+ /* List containing poll wait queues */
+ struct list_head pwqlist;
+
+ /* The "container" of this item */
+ struct eventpoll *ep;
+
+ /* List header used to link this item to the "struct file" items list */
+ struct list_head fllink;
+
+ /* The structure that describe the interested events and the source fd */
+ struct epoll_event event;
+};
+
/*
* This structure is stored inside the "private_data" member of the file
* structure and rapresent the main data sructure for the eventpoll
*/
struct eventpoll {
/* Protect the this structure access */
- rwlock_t lock;
+ spinlock_t lock;
/*
- * This semaphore is used to ensure that files are not removed
- * while epoll is using them. This is read-held during the event
- * collection loop and it is write-held during the file cleanup
- * path, the epoll file exit code and the ctl operations.
+ * This mutex is used to ensure that files are not removed
+ * while epoll is using them. This is held during the event
+ * collection loop, the file cleanup path, the epoll file exit
+ * code and the ctl operations.
*/
- struct rw_semaphore sem;
+ struct mutex mtx;
/* Wait queue used by sys_epoll_wait() */
wait_queue_head_t wq;
/* List of ready file descriptors */
struct list_head rdllist;
- /* RB-Tree root used to store monitored fd structs */
+ /* RB tree root used to store monitored fd structs */
struct rb_root rbr;
+
+ /*
+ * This is a single linked list that chains all the "struct epitem" that
+ * happened while transfering ready events to userspace w/out
+ * holding ->lock.
+ */
+ struct epitem *ovflist;
};
/* Wait structure used by the poll hooks */
wait_queue_head_t *whead;
};
-/*
- * Each file descriptor added to the eventpoll interface will
- * have an entry of this type linked to the "rbr" RB tree.
- */
-struct epitem {
- /* RB-Tree node used to link this structure to the eventpoll rb-tree */
- struct rb_node rbn;
-
- /* List header used to link this structure to the eventpoll ready list */
- struct list_head rdllink;
-
- /* The file descriptor information this item refers to */
- struct epoll_filefd ffd;
-
- /* Number of active wait queue attached to poll operations */
- int nwait;
-
- /* List containing poll wait queues */
- struct list_head pwqlist;
-
- /* The "container" of this item */
- struct eventpoll *ep;
-
- /* The structure that describe the interested events and the source fd */
- struct epoll_event event;
-
- /*
- * Used to keep track of the usage count of the structure. This avoids
- * that the structure will desappear from underneath our processing.
- */
- atomic_t usecnt;
-
- /* List header used to link this item to the "struct file" items list */
- struct list_head fllink;
-};
-
/* Wrapper struct used by poll queueing */
struct ep_pqueue {
poll_table pt;
};
/*
- * This semaphore is used to serialize ep_free() and eventpoll_release_file().
+ * This mutex is used to serialize ep_free() and eventpoll_release_file().
*/
static struct mutex epmutex;
static struct kmem_cache *pwq_cache __read_mostly;
-/* Setup the structure that is used as key for the rb-tree */
+/* Setup the structure that is used as key for the RB tree */
static inline void ep_set_ffd(struct epoll_filefd *ffd,
struct file *file, int fd)
{
ffd->fd = fd;
}
-/* Compare rb-tree keys */
+/* Compare RB tree keys */
static inline int ep_cmp_ffd(struct epoll_filefd *p1,
struct epoll_filefd *p2)
{
(p1->file < p2->file ? -1 : p1->fd - p2->fd));
}
-/* Special initialization for the rb-tree node to detect linkage */
+/* Special initialization for the RB tree node to detect linkage */
static inline void ep_rb_initnode(struct rb_node *n)
{
rb_set_parent(n, n);
}
-/* Removes a node from the rb-tree and marks it for a fast is-linked check */
+/* Removes a node from the RB tree and marks it for a fast is-linked check */
static inline void ep_rb_erase(struct rb_node *n, struct rb_root *r)
{
rb_erase(n, r);
rb_set_parent(n, n);
}
-/* Fast check to verify that the item is linked to the main rb-tree */
+/* Fast check to verify that the item is linked to the main RB tree */
static inline int ep_rb_linked(struct rb_node *n)
{
return rb_parent(n) != n;
int wake_nests = 0;
unsigned long flags;
struct task_struct *this_task = current;
- struct list_head *lsthead = &psw->wake_task_list, *lnk;
+ struct list_head *lsthead = &psw->wake_task_list;
struct wake_task_node *tncur;
struct wake_task_node tnode;
spin_lock_irqsave(&psw->lock, flags);
/* Try to see if the current task is already inside this wakeup call */
- list_for_each(lnk, lsthead) {
- tncur = list_entry(lnk, struct wake_task_node, llink);
+ list_for_each_entry(tncur, lsthead, llink) {
if (tncur->wq == wq ||
(tncur->task == this_task && ++wake_nests > EP_MAX_POLLWAKE_NESTS)) {
}
}
-/*
- * Unlink the "struct epitem" from all places it might have been hooked up.
- * This function must be called with write IRQ lock on "ep->lock".
- */
-static int ep_unlink(struct eventpoll *ep, struct epitem *epi)
-{
- int error;
-
- /*
- * It can happen that this one is called for an item already unlinked.
- * The check protect us from doing a double unlink ( crash ).
- */
- error = -ENOENT;
- if (!ep_rb_linked(&epi->rbn))
- goto error_return;
-
- /*
- * Clear the event mask for the unlinked item. This will avoid item
- * notifications to be sent after the unlink operation from inside
- * the kernel->userspace event transfer loop.
- */
- epi->event.events = 0;
-
- /*
- * At this point is safe to do the job, unlink the item from our rb-tree.
- * This operation togheter with the above check closes the door to
- * double unlinks.
- */
- ep_rb_erase(&epi->rbn, &ep->rbr);
-
- /*
- * If the item we are going to remove is inside the ready file descriptors
- * we want to remove it from this list to avoid stale events.
- */
- if (ep_is_linked(&epi->rdllink))
- list_del_init(&epi->rdllink);
-
- error = 0;
-error_return:
-
- DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_unlink(%p, %p) = %d\n",
- current, ep, epi->ffd.file, error));
-
- return error;
-}
-
-/*
- * Increment the usage count of the "struct epitem" making it sure
- * that the user will have a valid pointer to reference.
- */
-static void ep_use_epitem(struct epitem *epi)
-{
- atomic_inc(&epi->usecnt);
-}
-
-/*
- * Decrement ( release ) the usage count by signaling that the user
- * has finished using the structure. It might lead to freeing the
- * structure itself if the count goes to zero.
- */
-static void ep_release_epitem(struct epitem *epi)
-{
- if (atomic_dec_and_test(&epi->usecnt))
- kmem_cache_free(epi_cache, epi);
-}
-
/*
* Removes a "struct epitem" from the eventpoll RB tree and deallocates
- * all the associated resources.
+ * all the associated resources. Must be called with "mtx" held.
*/
static int ep_remove(struct eventpoll *ep, struct epitem *epi)
{
- int error;
unsigned long flags;
struct file *file = epi->ffd.file;
list_del_init(&epi->fllink);
spin_unlock(&file->f_ep_lock);
- /* We need to acquire the write IRQ lock before calling ep_unlink() */
- write_lock_irqsave(&ep->lock, flags);
-
- /* Really unlink the item from the RB tree */
- error = ep_unlink(ep, epi);
-
- write_unlock_irqrestore(&ep->lock, flags);
+ if (ep_rb_linked(&epi->rbn))
+ ep_rb_erase(&epi->rbn, &ep->rbr);
- if (error)
- goto error_return;
+ spin_lock_irqsave(&ep->lock, flags);
+ if (ep_is_linked(&epi->rdllink))
+ list_del_init(&epi->rdllink);
+ spin_unlock_irqrestore(&ep->lock, flags);
/* At this point it is safe to free the eventpoll item */
- ep_release_epitem(epi);
+ kmem_cache_free(epi_cache, epi);
- error = 0;
-error_return:
- DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p) = %d\n",
- current, ep, file, error));
+ DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_remove(%p, %p)\n",
+ current, ep, file));
- return error;
+ return 0;
}
static void ep_free(struct eventpoll *ep)
/*
* We need to lock this because we could be hit by
* eventpoll_release_file() while we're freeing the "struct eventpoll".
- * We do not need to hold "ep->sem" here because the epoll file
+ * We do not need to hold "ep->mtx" here because the epoll file
* is on the way to be removed and no one has references to it
* anymore. The only hit might come from eventpoll_release_file() but
* holding "epmutex" is sufficent here.
/*
* Walks through the whole tree by freeing each "struct epitem". At this
* point we are sure no poll callbacks will be lingering around, and also by
- * write-holding "sem" we can be sure that no file cleanup code will hit
+ * holding "epmutex" we can be sure that no file cleanup code will hit
* us during this operation. So we can avoid the lock on "ep->lock".
*/
- while ((rbp = rb_first(&ep->rbr)) != 0) {
+ while ((rbp = rb_first(&ep->rbr)) != NULL) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_remove(ep, epi);
}
mutex_unlock(&epmutex);
+ mutex_destroy(&ep->mtx);
+ kfree(ep);
}
static int ep_eventpoll_release(struct inode *inode, struct file *file)
{
struct eventpoll *ep = file->private_data;
- if (ep) {
+ if (ep)
ep_free(ep);
- kfree(ep);
- }
DNPRINTK(3, (KERN_INFO "[%p] eventpoll: close() ep=%p\n", current, ep));
return 0;
poll_wait(file, &ep->poll_wait, wait);
/* Check our condition */
- read_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
if (!list_empty(&ep->rdllist))
pollflags = POLLIN | POLLRDNORM;
- read_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
return pollflags;
}
* We don't want to get "file->f_ep_lock" because it is not
* necessary. It is not necessary because we're in the "struct file"
* cleanup path, and this means that noone is using this file anymore.
- * The only hit might come from ep_free() but by holding the semaphore
+ * So, for example, epoll_ctl() cannot hit here sicne if we reach this
+ * point, the file counter already went to zero and fget() would fail.
+ * The only hit might come from ep_free() but by holding the mutex
* will correctly serialize the operation. We do need to acquire
- * "ep->sem" after "epmutex" because ep_remove() requires it when called
+ * "ep->mtx" after "epmutex" because ep_remove() requires it when called
* from anywhere but ep_free().
*/
mutex_lock(&epmutex);
ep = epi->ep;
list_del_init(&epi->fllink);
- down_write(&ep->sem);
+ mutex_lock(&ep->mtx);
ep_remove(ep, epi);
- up_write(&ep->sem);
+ mutex_unlock(&ep->mtx);
}
mutex_unlock(&epmutex);
if (!ep)
return -ENOMEM;
- rwlock_init(&ep->lock);
- init_rwsem(&ep->sem);
+ spin_lock_init(&ep->lock);
+ mutex_init(&ep->mtx);
init_waitqueue_head(&ep->wq);
init_waitqueue_head(&ep->poll_wait);
INIT_LIST_HEAD(&ep->rdllist);
ep->rbr = RB_ROOT;
+ ep->ovflist = EP_UNACTIVE_PTR;
*pep = ep;
}
/*
- * Search the file inside the eventpoll tree. It add usage count to
- * the returned item, so the caller must call ep_release_epitem()
- * after finished using the "struct epitem".
+ * Search the file inside the eventpoll tree. The RB tree operations
+ * are protected by the "mtx" mutex, and ep_find() must be called with
+ * "mtx" held.
*/
static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
{
int kcmp;
- unsigned long flags;
struct rb_node *rbp;
struct epitem *epi, *epir = NULL;
struct epoll_filefd ffd;
ep_set_ffd(&ffd, file, fd);
- read_lock_irqsave(&ep->lock, flags);
for (rbp = ep->rbr.rb_node; rbp; ) {
epi = rb_entry(rbp, struct epitem, rbn);
kcmp = ep_cmp_ffd(&ffd, &epi->ffd);
else if (kcmp < 0)
rbp = rbp->rb_left;
else {
- ep_use_epitem(epi);
epir = epi;
break;
}
}
- read_unlock_irqrestore(&ep->lock, flags);
DNPRINTK(3, (KERN_INFO "[%p] eventpoll: ep_find(%p) -> %p\n",
current, file, epir));
DNPRINTK(3, (KERN_INFO "[%p] eventpoll: poll_callback(%p) epi=%p ep=%p\n",
current, epi->ffd.file, epi, ep));
- write_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
/*
* If the event mask does not contain any poll(2) event, we consider the
* until the next EPOLL_CTL_MOD will be issued.
*/
if (!(epi->event.events & ~EP_PRIVATE_BITS))
- goto is_disabled;
+ goto out_unlock;
+
+ /*
+ * If we are trasfering events to userspace, we can hold no locks
+ * (because we're accessing user memory, and because of linux f_op->poll()
+ * semantics). All the events that happens during that period of time are
+ * chained in ep->ovflist and requeued later on.
+ */
+ if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) {
+ if (epi->next == EP_UNACTIVE_PTR) {
+ epi->next = ep->ovflist;
+ ep->ovflist = epi;
+ }
+ goto out_unlock;
+ }
/* If this file is already in the ready list we exit soon */
if (ep_is_linked(&epi->rdllink))
if (waitqueue_active(&ep->poll_wait))
pwake++;
-is_disabled:
- write_unlock_irqrestore(&ep->lock, flags);
+out_unlock:
+ spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
rb_insert_color(&epi->rbn, &ep->rbr);
}
+/*
+ * Must be called with "mtx" held.
+ */
static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
struct file *tfile, int fd)
{
epi->ep = ep;
ep_set_ffd(&epi->ffd, tfile, fd);
epi->event = *event;
- atomic_set(&epi->usecnt, 1);
epi->nwait = 0;
+ epi->next = EP_UNACTIVE_PTR;
/* Initialize the poll table using the queue callback */
epq.epi = epi;
/*
* Attach the item to the poll hooks and get current event bits.
* We can safely use the file* here because its usage count has
- * been increased by the caller of this function.
+ * been increased by the caller of this function. Note that after
+ * this operation completes, the poll callback can start hitting
+ * the new item.
*/
revents = tfile->f_op->poll(tfile, &epq.pt);
list_add_tail(&epi->fllink, &tfile->f_ep_links);
spin_unlock(&tfile->f_ep_lock);
- /* We have to drop the new item inside our item list to keep track of it */
- write_lock_irqsave(&ep->lock, flags);
-
- /* Add the current item to the rb-tree */
+ /*
+ * Add the current item to the RB tree. All RB tree operations are
+ * protected by "mtx", and ep_insert() is called with "mtx" held.
+ */
ep_rbtree_insert(ep, epi);
+ /* We have to drop the new item inside our item list to keep track of it */
+ spin_lock_irqsave(&ep->lock, flags);
+
/* If the file is already "ready" we drop it inside the ready list */
if ((revents & event->events) && !ep_is_linked(&epi->rdllink)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
pwake++;
}
- write_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
/*
* We need to do this because an event could have been arrived on some
- * allocated wait queue.
+ * allocated wait queue. Note that we don't care about the ep->ovflist
+ * list, since that is used/cleaned only inside a section bound by "mtx".
+ * And ep_insert() is called with "mtx" held.
*/
- write_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
if (ep_is_linked(&epi->rdllink))
list_del_init(&epi->rdllink);
- write_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
kmem_cache_free(epi_cache, epi);
error_return:
/*
* Modify the interest event mask by dropping an event if the new mask
- * has a match in the current file status.
+ * has a match in the current file status. Must be called with "mtx" held.
*/
static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_event *event)
{
*/
revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
- write_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
/* Copy the data member from inside the lock */
epi->event.data = event->data;
/*
- * If the item is not linked to the RB tree it means that it's on its
- * way toward the removal. Do nothing in this case.
+ * If the item is "hot" and it is not registered inside the ready
+ * list, push it inside.
*/
- if (ep_rb_linked(&epi->rbn)) {
- /*
- * If the item is "hot" and it is not registered inside the ready
- * list, push it inside. If the item is not "hot" and it is currently
- * registered inside the ready list, unlink it.
- */
- if (revents & event->events) {
- if (!ep_is_linked(&epi->rdllink)) {
- list_add_tail(&epi->rdllink, &ep->rdllist);
-
- /* Notify waiting tasks that events are available */
- if (waitqueue_active(&ep->wq))
- __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
- TASK_INTERRUPTIBLE);
- if (waitqueue_active(&ep->poll_wait))
- pwake++;
- }
+ if (revents & event->events) {
+ if (!ep_is_linked(&epi->rdllink)) {
+ list_add_tail(&epi->rdllink, &ep->rdllist);
+
+ /* Notify waiting tasks that events are available */
+ if (waitqueue_active(&ep->wq))
+ __wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
+ TASK_INTERRUPTIBLE);
+ if (waitqueue_active(&ep->poll_wait))
+ pwake++;
}
}
-
- write_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
return 0;
}
-/*
- * This function is called without holding the "ep->lock" since the call to
- * __copy_to_user() might sleep, and also f_op->poll() might reenable the IRQ
- * because of the way poll() is traditionally implemented in Linux.
- */
-static int ep_send_events(struct eventpoll *ep, struct list_head *txlist,
- struct epoll_event __user *events, int maxevents)
+static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *events,
+ int maxevents)
{
int eventcnt, error = -EFAULT, pwake = 0;
unsigned int revents;
unsigned long flags;
- struct epitem *epi;
- struct list_head injlist;
+ struct epitem *epi, *nepi;
+ struct list_head txlist;
+
+ INIT_LIST_HEAD(&txlist);
+
+ /*
+ * We need to lock this because we could be hit by
+ * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
+ */
+ mutex_lock(&ep->mtx);
- INIT_LIST_HEAD(&injlist);
+ /*
+ * Steal the ready list, and re-init the original one to the
+ * empty list. Also, set ep->ovflist to NULL so that events
+ * happening while looping w/out locks, are not lost. We cannot
+ * have the poll callback to queue directly on ep->rdllist,
+ * because we are doing it in the loop below, in a lockless way.
+ */
+ spin_lock_irqsave(&ep->lock, flags);
+ list_splice(&ep->rdllist, &txlist);
+ INIT_LIST_HEAD(&ep->rdllist);
+ ep->ovflist = NULL;
+ spin_unlock_irqrestore(&ep->lock, flags);
/*
* We can loop without lock because this is a task private list.
* We just splice'd out the ep->rdllist in ep_collect_ready_items().
- * Items cannot vanish during the loop because we are holding "sem" in
- * read.
+ * Items cannot vanish during the loop because we are holding "mtx".
*/
- for (eventcnt = 0; !list_empty(txlist) && eventcnt < maxevents;) {
- epi = list_first_entry(txlist, struct epitem, rdllink);
- prefetch(epi->rdllink.next);
+ for (eventcnt = 0; !list_empty(&txlist) && eventcnt < maxevents;) {
+ epi = list_first_entry(&txlist, struct epitem, rdllink);
+
+ list_del_init(&epi->rdllink);
/*
* Get the ready file event set. We can safely use the file
- * because we are holding the "sem" in read and this will
- * guarantee that both the file and the item will not vanish.
+ * because we are holding the "mtx" and this will guarantee
+ * that both the file and the item will not vanish.
*/
revents = epi->ffd.file->f_op->poll(epi->ffd.file, NULL);
revents &= epi->event.events;
/*
* Is the event mask intersect the caller-requested one,
* deliver the event to userspace. Again, we are holding
- * "sem" in read, so no operations coming from userspace
- * can change the item.
+ * "mtx", so no operations coming from userspace can change
+ * the item.
*/
if (revents) {
if (__put_user(revents,
epi->event.events &= EP_PRIVATE_BITS;
eventcnt++;
}
-
/*
- * This is tricky. We are holding the "sem" in read, and this
- * means that the operations that can change the "linked" status
- * of the epoll item (epi->rbn and epi->rdllink), cannot touch
- * them. Also, since we are "linked" from a epi->rdllink POV
- * (the item is linked to our transmission list we just
- * spliced), the ep_poll_callback() cannot touch us either,
- * because of the check present in there. Another parallel
- * epoll_wait() will not get the same result set, since we
- * spliced the ready list before. Note that list_del() still
- * shows the item as linked to the test in ep_poll_callback().
+ * At this point, noone can insert into ep->rdllist besides
+ * us. The epoll_ctl() callers are locked out by us holding
+ * "mtx" and the poll callback will queue them in ep->ovflist.
*/
- list_del(&epi->rdllink);
if (!(epi->event.events & EPOLLET) &&
- (revents & epi->event.events))
- list_add_tail(&epi->rdllink, &injlist);
- else {
- /*
- * Be sure the item is totally detached before re-init
- * the list_head. After INIT_LIST_HEAD() is committed,
- * the ep_poll_callback() can requeue the item again,
- * but we don't care since we are already past it.
- */
- smp_mb();
- INIT_LIST_HEAD(&epi->rdllink);
- }
+ (revents & epi->event.events))
+ list_add_tail(&epi->rdllink, &ep->rdllist);
}
error = 0;
- errxit:
+errxit:
+ spin_lock_irqsave(&ep->lock, flags);
/*
- * If the re-injection list or the txlist are not empty, re-splice
- * them to the ready list and do proper wakeups.
+ * During the time we spent in the loop above, some other events
+ * might have been queued by the poll callback. We re-insert them
+ * here (in case they are not already queued, or they're one-shot).
*/
- if (!list_empty(&injlist) || !list_empty(txlist)) {
- write_lock_irqsave(&ep->lock, flags);
+ for (nepi = ep->ovflist; (epi = nepi) != NULL;
+ nepi = epi->next, epi->next = EP_UNACTIVE_PTR) {
+ if (!ep_is_linked(&epi->rdllink) &&
+ (epi->event.events & ~EP_PRIVATE_BITS))
+ list_add_tail(&epi->rdllink, &ep->rdllist);
+ }
+ /*
+ * We need to set back ep->ovflist to EP_UNACTIVE_PTR, so that after
+ * releasing the lock, events will be queued in the normal way inside
+ * ep->rdllist.
+ */
+ ep->ovflist = EP_UNACTIVE_PTR;
+
+ /*
+ * In case of error in the event-send loop, or in case the number of
+ * ready events exceeds the userspace limit, we need to splice the
+ * "txlist" back inside ep->rdllist.
+ */
+ list_splice(&txlist, &ep->rdllist);
- list_splice(txlist, &ep->rdllist);
- list_splice(&injlist, &ep->rdllist);
+ if (!list_empty(&ep->rdllist)) {
/*
- * Wake up ( if active ) both the eventpoll wait list and the ->poll()
- * wait list.
+ * Wake up (if active) both the eventpoll wait list and the ->poll()
+ * wait list (delayed after we release the lock).
*/
if (waitqueue_active(&ep->wq))
__wake_up_locked(&ep->wq, TASK_UNINTERRUPTIBLE |
TASK_INTERRUPTIBLE);
if (waitqueue_active(&ep->poll_wait))
pwake++;
-
- write_unlock_irqrestore(&ep->lock, flags);
}
+ spin_unlock_irqrestore(&ep->lock, flags);
+
+ mutex_unlock(&ep->mtx);
/* We have to call this outside the lock */
if (pwake)
return eventcnt == 0 ? error: eventcnt;
}
-/*
- * Perform the transfer of events to user space.
- */
-static int ep_events_transfer(struct eventpoll *ep,
- struct epoll_event __user *events, int maxevents)
-{
- int eventcnt;
- unsigned long flags;
- struct list_head txlist;
-
- INIT_LIST_HEAD(&txlist);
-
- /*
- * We need to lock this because we could be hit by
- * eventpoll_release_file() and epoll_ctl(EPOLL_CTL_DEL).
- */
- down_read(&ep->sem);
-
- /*
- * Steal the ready list, and re-init the original one to the
- * empty list.
- */
- write_lock_irqsave(&ep->lock, flags);
- list_splice(&ep->rdllist, &txlist);
- INIT_LIST_HEAD(&ep->rdllist);
- write_unlock_irqrestore(&ep->lock, flags);
-
- /* Build result set in userspace */
- eventcnt = ep_send_events(ep, &txlist, events, maxevents);
-
- up_read(&ep->sem);
-
- return eventcnt;
-}
-
static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int maxevents, long timeout)
{
MAX_SCHEDULE_TIMEOUT : (timeout * HZ + 999) / 1000;
retry:
- write_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
res = 0;
if (list_empty(&ep->rdllist)) {
* ep_poll_callback() when events will become available.
*/
init_waitqueue_entry(&wait, current);
+ wait.flags |= WQ_FLAG_EXCLUSIVE;
__add_wait_queue(&ep->wq, &wait);
for (;;) {
break;
}
- write_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
jtimeout = schedule_timeout(jtimeout);
- write_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
}
__remove_wait_queue(&ep->wq, &wait);
/* Is it worth to try to dig for events ? */
eavail = !list_empty(&ep->rdllist);
- write_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
/*
* Try to transfer events to user space. In case we get 0 events and
* more luck.
*/
if (!res && eavail &&
- !(res = ep_events_transfer(ep, events, maxevents)) && jtimeout)
+ !(res = ep_send_events(ep, events, maxevents)) && jtimeout)
goto retry;
return res;
}
/*
- * It opens an eventpoll file descriptor by suggesting a storage of "size"
- * file descriptors. The size parameter is just an hint about how to size
- * data structures. It won't prevent the user to store more than "size"
- * file descriptors inside the epoll interface. It is the kernel part of
- * the userspace epoll_create(2).
+ * It opens an eventpoll file descriptor. The "size" parameter is there
+ * for historical reasons, when epoll was using an hash instead of an
+ * RB tree. With the current implementation, the "size" parameter is ignored
+ * (besides sanity checks).
*/
asmlinkage long sys_epoll_create(int size)
{
error_free:
ep_free(ep);
- kfree(ep);
error_return:
DNPRINTK(3, (KERN_INFO "[%p] eventpoll: sys_epoll_create(%d) = %d\n",
current, size, error));
/*
* The following function implements the controller interface for
* the eventpoll file that enables the insertion/removal/change of
- * file descriptors inside the interest set. It represents
- * the kernel part of the user space epoll_ctl(2).
+ * file descriptors inside the interest set.
*/
asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
struct epoll_event __user *event)
*/
ep = file->private_data;
- down_write(&ep->sem);
+ mutex_lock(&ep->mtx);
- /* Try to lookup the file inside our RB tree */
+ /*
+ * Try to lookup the file inside our RB tree, Since we grabbed "mtx"
+ * above, we can be sure to be able to use the item looked up by
+ * ep_find() till we release the mutex.
+ */
epi = ep_find(ep, tfile, fd);
error = -EINVAL;
error = -ENOENT;
break;
}
- /*
- * The function ep_find() increments the usage count of the structure
- * so, if this is not NULL, we need to release it.
- */
- if (epi)
- ep_release_epitem(epi);
- up_write(&ep->sem);
+ mutex_unlock(&ep->mtx);
error_tgt_fput:
fput(tfile);
if (sigmask) {
if (error == -EINTR) {
memcpy(¤t->saved_sigmask, &sigsaved,
- sizeof(sigsaved));
+ sizeof(sigsaved));
set_thread_flag(TIF_RESTORE_SIGMASK);
} else
sigprocmask(SIG_SETMASK, &sigsaved, NULL);
/* Allocates slab cache used to allocate "struct epitem" items */
epi_cache = kmem_cache_create("eventpoll_epi", sizeof(struct epitem),
0, SLAB_HWCACHE_ALIGN|EPI_SLAB_DEBUG|SLAB_PANIC,
- NULL, NULL);
+ NULL);
/* Allocates slab cache used to allocate "struct eppoll_entry" */
pwq_cache = kmem_cache_create("eventpoll_pwq",
sizeof(struct eppoll_entry), 0,
- EPI_SLAB_DEBUG|SLAB_PANIC, NULL, NULL);
+ EPI_SLAB_DEBUG|SLAB_PANIC, NULL);
return 0;
}
git.samba.org / sfrench / cifs-2.6.git / blobdiff