The patch titled
Subject: epoll: lock ep->mtx in ep_free to silence lockdep
has been added to the -mm tree. Its filename is
epoll-lock-ep-mtx-in-ep_free-to-silence-lockdep.patch
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From: Eric Wong <normalperson@xxxxxxxx>
Subject: epoll: lock ep->mtx in ep_free to silence lockdep
Technically we do not need to hold ep->mtx during ep_free since we are
certain there are no other users of ep at that point. However, lockdep
complains with a "suspicious rcu_dereference_check() usage!" message; so
lock the mutex before ep_remove to silence the warning.
Signed-off-by: Eric Wong <normalperson@xxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Arve Hjønnevåg <arve@xxxxxxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Cc: NeilBrown <neilb@xxxxxxx>,
Cc: Rafael J. Wysocki <rjw@xxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 4 ++++
1 file changed, 4 insertions(+)
diff -puN fs/eventpoll.c~epoll-lock-ep-mtx-in-ep_free-to-silence-lockdep fs/eventpoll.c
--- a/fs/eventpoll.c~epoll-lock-ep-mtx-in-ep_free-to-silence-lockdep
+++ a/fs/eventpoll.c
@@ -776,11 +776,15 @@ static void ep_free(struct eventpoll *ep
* point we are sure no poll callbacks will be lingering around, and also by
* 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".
+ * We do not need to lock ep->mtx, either, we only do it to prevent
+ * a lockdep warning.
*/
+ mutex_lock(&ep->mtx);
while ((rbp = rb_first(&ep->rbr)) != NULL) {
epi = rb_entry(rbp, struct epitem, rbn);
ep_remove(ep, epi);
}
+ mutex_unlock(&ep->mtx);
mutex_unlock(&epmutex);
mutex_destroy(&ep->mtx);
_
Patches currently in -mm which might be from normalperson@xxxxxxxx are
epoll-trim-epitem-by-one-cache-line-on-x86_64.patch
epoll-trim-epitem-by-one-cache-line-on-x86_64-fix.patch
epoll-trim-epitem-by-one-cache-line-on-x86_64-fix-fix.patch
epoll-use-rcu-to-protect-wakeup_source-in-epitem.patch
epoll-lock-ep-mtx-in-ep_free-to-silence-lockdep.patch
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