linux-kernel - Re: [patch] fs, epoll: short circuit fetching events if thread has been killed

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Date:   Tue, 9 May 2017 16:05:20 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Davide Libenzi <davidel@...ilserver.org>
Subject: Re: [patch] fs, epoll: short circuit fetching events if thread has
 been killed

On Wed, 3 May 2017 17:22:53 -0700 (PDT) David Rientjes <rientjes@...gle.com> wrote:

> 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.

Any thoughts on the priority of this?  -stable?  If so, why?