The patch titled Subject: fs/epoll: restore waking from ep_done_scan() has been added to the -mm tree. Its filename is fs-epoll-restore-waking-from-ep_done_scan.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/fs-epoll-restore-waking-from-ep_done_scan.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/fs-epoll-restore-waking-from-ep_done_scan.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/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Davidlohr Bueso <dave@xxxxxxxxxxxx> Subject: fs/epoll: restore waking from ep_done_scan() 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@xxxxxxxxxxxx Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Jason Baron <jbaron@xxxxxxxxxx> Cc: Roman Penyaev <rpenyaev@xxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/eventpoll.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/fs/eventpoll.c~fs-epoll-restore-waking-from-ep_done_scan +++ a/fs/eventpoll.c @@ -657,6 +657,12 @@ static void ep_done_scan(struct eventpol */ 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); } _ Patches currently in -mm which might be from dave@xxxxxxxxxxxx are kselftest-introduce-new-epoll-test-case.patch fs-epoll-restore-waking-from-ep_done_scan.patch