linux-kernel - Re: [PATCH vfs/vfs.fixes v2] eventpoll: Set epoll timeout if it's in the future

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Message-ID: <aBAEDdvoazY6UGbS@LQ3V64L9R2>
Date: Mon, 28 Apr 2025 15:41:17 -0700
From: Joe Damato <jdamato@...tly.com>
To: Carlos Llamas <cmllamas@...gle.com>
Cc: Jan Kara <jack@...e.cz>, Christian Brauner <brauner@...nel.org>,
	linux-fsdevel@...r.kernel.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Sridhar Samudrala <sridhar.samudrala@...el.com>,
	Alexander Duyck <alexander.h.duyck@...el.com>,
	open list <linux-kernel@...r.kernel.org>,
	Tudor Ambarus <tudor.ambarus@...aro.org>,
	William McVicker <willmcvicker@...gle.com>
Subject: Re: [PATCH vfs/vfs.fixes v2] eventpoll: Set epoll timeout if it's in
 the future

On Mon, Apr 28, 2025 at 10:32:31PM +0000, Carlos Llamas wrote:
> On Mon, Apr 28, 2025 at 09:50:02AM -0700, Joe Damato wrote:
> > Thank you for spotting that and sorry for the trouble.
> 
> This was also flagged by our Android's epoll_pwait2 tests here:
> https://android.googlesource.com/platform/bionic/+/refs/heads/main/tests/sys_epoll_test.cpp
> They would all timeout, so the hang reported by Christian fits.
> 
> 
> > Christian / Jan what would be the correct way for me to deal with
> > this? Would it be to post a v3 (re-submitting the patch in its
> > entirety) or to post a new patch that fixes the original and lists
> > the commit sha from vfs.fixes with a Fixes tag ?
> 
> The original commit has landed in mainline already, so it needs to be
> new patch at this point. If if helps, here is the tag:
> Fixes: 0a65bc27bd64 ("eventpoll: Set epoll timeout if it's in the future")
> 
> > diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> > index 4bc264b854c4..1a5d1147f082 100644
> > --- a/fs/eventpoll.c
> > +++ b/fs/eventpoll.c
> > @@ -2111,7 +2111,9 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
> > 
> >                 write_unlock_irq(&ep->lock);
> > 
> > -               if (!eavail && ep_schedule_timeout(to))
> > +               if (!ep_schedule_timeout(to))
> > +                       timed_out = 1;
> > +               else if (!eavail)
> >                         timed_out = !schedule_hrtimeout_range(to, slack,
> >                                                               HRTIMER_MODE_ABS);
> >                 __set_current_state(TASK_RUNNING);
> 
> I've ran your change through our internal CI and I confirm it fixes the
> hangs seen on our end. If you send the fix feel free to add:
> 
> Tested-by: Carlos Llamas <cmllamas@...gle.com>

Thanks, will do.

I was waiting to hear back from Christian / Jan if they are OK with
the proposed fix before submitting something, but glad to hear it
fixes the issue for you. Sorry for the trouble.