diff options
author | Tony Battersby <tonyb@cybernetics.com> | 2009-03-31 22:24:15 (GMT) |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2009-04-01 15:59:19 (GMT) |
commit | d1bc90dd5d037079f96b3327f943eb6ae8ef7491 (patch) | |
tree | 0380bd32cee23815b214d81a12b618140c544799 /fs | |
parent | d0305882825784e74f68a56eee6c3a812a99f235 (diff) | |
download | linux-fsl-qoriq-d1bc90dd5d037079f96b3327f943eb6ae8ef7491.tar.xz |
epoll: remove unnecessary xchg
xchg in ep_unregister_pollwait() is unnecessary because it is protected by
either epmutex or ep->mtx (the same protection as ep_remove()).
If xchg was necessary, it would be insufficient to protect against
problems: if multiple concurrent calls to ep_unregister_pollwait() were
possible then a second caller that returns without doing anything because
nwait == 0 could return before the waitqueues are removed by the first
caller, which looks like it could lead to problematic races with
ep_poll_callback().
So remove xchg and add comments about the locking.
Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Acked-by: Davide Libenzi <davidel@xmailserver.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs')
-rw-r--r-- | fs/eventpoll.c | 22 |
1 files changed, 8 insertions, 14 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c index c806a0c..64c5503 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -394,27 +394,21 @@ static void ep_poll_safewake(wait_queue_head_t *wq) } /* - * This function unregister poll callbacks from the associated file descriptor. - * Since this must be called without holding "ep->lock" the atomic exchange trick - * will protect us from multiple unregister. + * This function unregisters poll callbacks from the associated file + * descriptor. Must be called with "mtx" held (or "epmutex" if called from + * ep_free). */ static void ep_unregister_pollwait(struct eventpoll *ep, struct epitem *epi) { - int nwait; struct list_head *lsthead = &epi->pwqlist; struct eppoll_entry *pwq; - /* This is called without locks, so we need the atomic exchange */ - nwait = xchg(&epi->nwait, 0); - - if (nwait) { - while (!list_empty(lsthead)) { - pwq = list_first_entry(lsthead, struct eppoll_entry, llink); + while (!list_empty(lsthead)) { + pwq = list_first_entry(lsthead, struct eppoll_entry, llink); - list_del_init(&pwq->llink); - remove_wait_queue(pwq->whead, &pwq->wait); - kmem_cache_free(pwq_cache, pwq); - } + list_del(&pwq->llink); + remove_wait_queue(pwq->whead, &pwq->wait); + kmem_cache_free(pwq_cache, pwq); } } |