The patch titled
Subject: fs, epoll: short circuit fetching events if thread has been killed
has been added to the -mm tree. Its filename is
fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed.patch
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------------------------------------------------------
From: David Rientjes <rientjes@xxxxxxxxxx>
Subject: fs, epoll: short circuit fetching events if thread has been killed
We've encountered zombies that are waiting for a thread to exit that are
looping in ep_poll() almost endlessly although there is a pending SIGKILL
as a result of a group exit.
This happens because we always find ep_events_available() and fetch more
events and never are able to check for signal_pending() that would break
from the loop and return -EINTR.
Special case fatal signals and break immediately to guarantee that we loop
to fetch more events and delay making a timely exit.
It would also be possible to simply move the check for signal_pending()
higher than checking for ep_events_available(), but there have been no
reports of delayed signal handling other than SIGKILL preventing zombies
from exiting that would be fixed by this.
Link: http://lkml.kernel.org/r/alpine.DEB.2.10.1705031722350.76784@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Davide Libenzi <davidel@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/eventpoll.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff -puN fs/eventpoll.c~fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed fs/eventpoll.c
--- a/fs/eventpoll.c~fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed
+++ a/fs/eventpoll.c
@@ -1748,6 +1748,16 @@ fetch_events:
* to TASK_INTERRUPTIBLE before doing the checks.
*/
set_current_state(TASK_INTERRUPTIBLE);
+ /*
+ * Always short-circuit for fatal signals to allow
+ * threads to make a timely exit without the chance of
+ * finding more events available and fetching
+ * repeatedly.
+ */
+ if (fatal_signal_pending(current)) {
+ res = -EINTR;
+ break;
+ }
if (ep_events_available(ep) || timed_out)
break;
if (signal_pending(current)) {
_
Patches currently in -mm which might be from rientjes@xxxxxxxxxx are
fs-epoll-short-circuit-fetching-events-if-thread-has-been-killed.patch
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