From: Eric Wong <normalperson@yhbt.net>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Hans Verkuil <hans.verkuil@cisco.com>,
Jiri Olsa <jolsa@redhat.com>, Jonathan Corbet <corbet@lwn.net>,
Al Viro <viro@zeniv.linux.org.uk>,
Davide Libenzi <davidel@xmailserver.org>,
Hans de Goede <hdegoede@redhat.com>,
Mauro Carvalho Chehab <mchehab@infradead.org>,
David Miller <davem@davemloft.net>,
Andrew Morton <akpm@linux-foundation.org>,
Andreas Voellmy <andreas.voellmy@yale.edu>,
"Junchang(Jason) Wang" <junchang.wang@yale.edu>,
Network Development <netdev@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] epoll: prevent missed events on EPOLL_CTL_MOD
Date: Wed, 2 Jan 2013 19:32:27 +0000 [thread overview]
Message-ID: <20130102193227.GA13566@dcvr.yhbt.net> (raw)
In-Reply-To: <1357153416.21409.17488.camel@edumazet-glaptop>
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Wed, 2013-01-02 at 18:40 +0000, Eric Wong wrote:
> > Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > > It seems the real problem is the epi->event.events = event->events;
> > > which is done without taking ep->lock
> >
> > Yes. I am hoping it is possible to do it without a lock there,
> > but your change is more obviously correct.
> >
> > > While a smp_mb() could reduce the race window, I believe there is still
> > > a race, and the following patch would close it.
> >
> > I'm not an experienced kernel hacker, can you describe where the race
> > would be?
>
> It would be for example in ep_send_events_proc() doing :
>
> if (epi->event.events & EPOLLONESHOT)
> epi->event.events &= EP_PRIVATE_BITS;
>
> And this could happen at the same time.
That modification in ep_send_events_proc() is protected by ep->mtx
(as is ep_modify()), though. Maybe there are other places, but I
don't see it.
next prev parent reply other threads:[~2013-01-02 19:32 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-28 1:45 ppoll() stuck on POLLIN while TCP peer is sending Eric Wong
2012-12-28 7:06 ` Eric Wong
2012-12-29 11:34 ` Eric Wong
2012-12-31 13:21 ` [PATCH] poll: prevent missed events if _qproc is NULL Eric Wong
2012-12-31 23:24 ` Eric Wong
2013-01-01 16:58 ` Junchang(Jason) Wang
2013-01-01 18:42 ` Eric Dumazet
2013-01-01 21:00 ` Eric Wong
2013-01-01 21:17 ` Eric Wong
2013-01-01 22:53 ` Linus Torvalds
2013-01-01 23:21 ` Junchang(Jason) Wang
2013-01-01 23:56 ` [PATCH] epoll: prevent missed events on EPOLL_CTL_MOD Eric Wong
2013-01-02 17:45 ` Eric Dumazet
2013-01-02 18:40 ` Eric Wong
2013-01-02 19:03 ` Eric Dumazet
2013-01-02 19:32 ` Eric Wong [this message]
2013-01-02 22:08 ` Eric Dumazet
2013-01-02 21:16 ` Eric Wong
2013-01-02 20:08 ` ppoll() stuck on POLLIN while TCP peer is sending Eric Wong
2013-01-02 20:47 ` Eric Wong
2013-01-03 13:41 ` Eric Dumazet
2013-01-03 18:32 ` Eric Wong
2013-01-03 23:45 ` Eric Wong
2013-01-04 0:26 ` Eric Wong
2013-01-04 3:52 ` Eric Wong
2013-01-04 16:01 ` Mel Gorman
2013-01-04 17:15 ` Eric Dumazet
2013-01-04 17:59 ` Eric Wong
2013-01-05 1:07 ` Eric Wong
2013-01-06 12:07 ` Eric Wong
2013-01-07 12:25 ` Mel Gorman
2013-01-07 22:38 ` Eric Dumazet
2013-01-08 0:21 ` Eric Wong
2013-01-07 22:38 ` Eric Wong
2013-01-08 20:14 ` Eric Wong
2013-01-08 22:43 ` Mel Gorman
2013-01-08 23:23 ` Eric Wong
2013-01-09 2:14 ` Eric Dumazet
2013-01-09 2:32 ` Eric Dumazet
2013-01-09 2:54 ` Eric Dumazet
2013-01-09 3:55 ` Eric Wong
2013-01-09 8:42 ` Eric Wong
2013-01-09 8:51 ` Eric Wong
2013-01-09 13:42 ` Mel Gorman
2013-01-09 13:37 ` Mel Gorman
2013-01-09 13:50 ` Mel Gorman
2013-01-10 9:25 ` Eric Wong
2013-01-10 19:42 ` Mel Gorman
2013-01-10 20:03 ` Eric Wong
2013-01-10 20:58 ` Eric Dumazet
2013-01-11 0:51 ` Eric Wong
2013-01-11 9:30 ` Mel Gorman
2013-01-09 21:29 ` Eric Wong
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