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Commit c7ea7630 authored by Davide Libenzi's avatar Davide Libenzi Committed by Linus Torvalds
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epoll locks changes and cleanups 

Changes the rwlock to a spinlock, and drops the use-count variable.
Operations are always bound by the mutex now, so the use-count is no more
needed.  For the same reason, the rwlock can become a simple spinlock.
Signed-off-by: default avatarDavide Libenzi <davidel@xmailserver.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d47de16c
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Inline Side-by-side
Showing with 73 additions and 161 deletions
fs/eventpoll.c
View file @ c7ea7630
/*
* 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
......@@ -44,8 +44,8 @@
* There are three level of locking required by epoll :
*
* 1) epmutex (mutex)
* 2) ep->mtx (mutes)
* 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
......@@ -140,6 +140,12 @@ struct epitem {
/* 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;
......@@ -152,23 +158,11 @@ struct epitem {
/* 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;
/*
* Works together "struct eventpoll"->ovflist in keeping the
* single linked chain of items.
*/
struct epitem *next;
/* The structure that describe the interested events and the source fd */
struct epoll_event event;
};
/*
......@@ -178,7 +172,7 @@ struct epitem {
*/
struct eventpoll {
/* Protect the this structure access */
rwlock_t lock;
spinlock_t lock;
/*
* This mutex is used to ensure that files are not removed
......@@ -393,79 +387,12 @@ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi)
}
}
/*
* 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;
......@@ -485,26 +412,21 @@ static int ep_remove(struct eventpoll *ep, struct epitem *epi)
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)
......@@ -574,10 +496,10 @@ static unsigned int ep_eventpoll_poll(struct file *file, poll_table *wait)
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;
}
......@@ -636,7 +558,7 @@ static int ep_alloc(struct eventpoll **pep)
if (!ep)
return -ENOMEM;
rwlock_init(&ep->lock);
spin_lock_init(&ep->lock);
mutex_init(&ep->mtx);
init_waitqueue_head(&ep->wq);
init_waitqueue_head(&ep->poll_wait);
......@@ -652,20 +574,18 @@ static int ep_alloc(struct eventpoll **pep)
}
/*
* 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);
......@@ -674,12 +594,10 @@ static struct epitem *ep_find(struct eventpoll *ep, struct file *file, int fd)
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));
......@@ -702,7 +620,7 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
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
......@@ -745,7 +663,7 @@ static int ep_poll_callback(wait_queue_t *wait, unsigned mode, int sync, void *k
pwake++;
out_unlock:
write_unlock_irqrestore(&ep->lock, flags);
spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
......@@ -796,6 +714,9 @@ static void ep_rbtree_insert(struct eventpoll *ep, struct epitem *epi)
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)
{
......@@ -816,7 +737,6 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
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;
......@@ -827,7 +747,9 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
/*
* 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);
......@@ -844,12 +766,15 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
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);
......@@ -861,7 +786,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
pwake++;
}
write_unlock_irqrestore(&ep->lock, flags);
spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
......@@ -879,10 +804,10 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
* We need to do this because an event could have been arrived on some
* allocated wait queue.
*/
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:
......@@ -891,7 +816,7 @@ static int ep_insert(struct eventpoll *ep, struct epoll_event *event,
/*
* 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)
{
......@@ -913,16 +838,11 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
*/
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 (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
......@@ -940,9 +860,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even
pwake++;
}
}
}
write_unlock_irqrestore(&ep->lock, flags);
spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
......@@ -975,11 +893,11 @@ static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *event
* have the poll callback to queue directly on ep->rdllist,
* because we are doing it in the loop below, in a lockless way.
*/
write_lock_irqsave(&ep->lock, flags);
spin_lock_irqsave(&ep->lock, flags);
list_splice(&ep->rdllist, &txlist);
INIT_LIST_HEAD(&ep->rdllist);
ep->ovflist = NULL;
write_unlock_irqrestore(&ep->lock, flags);
spin_unlock_irqrestore(&ep->lock, flags);
/*
* We can loop without lock because this is a task private list.
......@@ -1028,7 +946,7 @@ static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *event
errxit:
write_lock_irqsave(&ep->lock, flags);
spin_lock_irqsave(&ep->lock, flags);
/*
* During the time we spent in the loop above, some other events
* might have been queued by the poll callback. We re-insert them
......@@ -1064,7 +982,7 @@ static int ep_send_events(struct eventpoll *ep, struct epoll_event __user *event
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
write_unlock_irqrestore(&ep->lock, flags);
spin_unlock_irqrestore(&ep->lock, flags);
mutex_unlock(&ep->mtx);
......@@ -1092,7 +1010,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
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)) {
......@@ -1119,9 +1037,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
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);
......@@ -1131,7 +1049,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
/* 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
......@@ -1276,12 +1194,6 @@ asmlinkage long sys_epoll_ctl(int epfd, int op, int fd,
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);
mutex_unlock(&ep->mtx);
error_tgt_fput:
......
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