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authorDavidlohr Bueso <dave@stgolabs.net>2021-05-07 03:04:07 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2021-05-07 04:24:13 +0200
commit7fab29e356309ff93a4b30ecc466129682ec190b (patch)
tree0c6398b206c31ee120110d5cb24bc0b21b314e73 /fs/eventpoll.c
parentkselftest: introduce new epoll test case (diff)
downloadlinux-7fab29e356309ff93a4b30ecc466129682ec190b.tar.xz
linux-7fab29e356309ff93a4b30ecc466129682ec190b.zip
fs/epoll: restore waking from ep_done_scan()
Commit 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll") changed the userspace visible behavior of exclusive waiters blocked on a common epoll descriptor upon a single event becoming ready. Previously, all tasks doing epoll_wait would awake, and now only one is awoken, potentially causing missed wakeups on applications that rely on this behavior, such as Apache Qpid. While the aforementioned commit aims at having only a wakeup single path in ep_poll_callback (with the exceptions of epoll_ctl cases), we need to restore the wakeup in what was the old ep_scan_ready_list() such that the next thread can be awoken, in a cascading style, after the waker's corresponding ep_send_events(). Link: https://lkml.kernel.org/r/20210405231025.33829-3-dave@stgolabs.net Fixes: 339ddb53d373 ("fs/epoll: remove unnecessary wakeups of nested epoll") Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Jason Baron <jbaron@akamai.com> Cc: Roman Penyaev <rpenyaev@suse.de> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'fs/eventpoll.c')
-rw-r--r--fs/eventpoll.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 73138ea68342..1e596e1d0bba 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -657,6 +657,12 @@ static void ep_done_scan(struct eventpoll *ep,
*/
list_splice(txlist, &ep->rdllist);
__pm_relax(ep->ws);
+
+ if (!list_empty(&ep->rdllist)) {
+ if (waitqueue_active(&ep->wq))
+ wake_up(&ep->wq);
+ }
+
write_unlock_irq(&ep->lock);
}