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. It fixes an issue for us where we have witnessed zombies sticking around for at least O(minutes), but considering the code has been like this forever and nobody else has complained that I have found, I would simply queue it up for 4.12. 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)) { _ -- 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
