The patch titled
epoll: remove unnecessary xchg
has been added to the -mm tree. Its filename is
epoll-remove-unnecessary-xchg.patch
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://userweb.kernel.org/~akpm/stuff/added-to-mm.txt to find
out what to do about this
The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/
------------------------------------------------------
Subject: epoll: remove unnecessary xchg
From: Tony Battersby <tonyb@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
Acked-by: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 22 ++++++++--------------
1 file changed, 8 insertions(+), 14 deletions(-)
diff -puN fs/eventpoll.c~epoll-remove-unnecessary-xchg fs/eventpoll.c
--- a/fs/eventpoll.c~epoll-remove-unnecessary-xchg
+++ a/fs/eventpoll.c
@@ -394,27 +394,21 @@ static void ep_poll_safewake(wait_queue_
}
/*
- * 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);
+ while (!list_empty(lsthead)) {
+ pwq = list_first_entry(lsthead, struct eppoll_entry, llink);
- if (nwait) {
- 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);
}
}
_
Patches currently in -mm which might be from tonyb@xxxxxxxxxxxxxxx are
origin.patch
linux-next.patch
vfs-improve-comment-describing-fget_light.patch
epoll-dont-use-current-in-irq-context.patch
epoll-remember-the-event-if-epoll_wait-returns-efault.patch
epoll-remove-unnecessary-xchg.patch
epoll-clean-up-ep_modify.patch
epoll-use-real-type-instead-of-void.patch
make-shm_get_stat-more-robust.patch
--
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
