From: Eric Wong <normalperson@yhbt.net>
To: linux-kernel@vger.kernel.org
Cc: 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>,
Eric Dumazet <eric.dumazet@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andreas Voellmy <andreas.voellmy@yale.edu>,
"Junchang(Jason) Wang" <junchang.wang@yale.edu>,
netdev@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] poll: prevent missed events if _qproc is NULL
Date: Mon, 31 Dec 2012 23:24:24 +0000 [thread overview]
Message-ID: <20121231232424.GA24235@dcvr.yhbt.net> (raw)
In-Reply-To: <1356960060-1263-1-git-send-email-normalperson@yhbt.net>
Eric Wong <normalperson@yhbt.net> wrote:
> This patch seems to fix my issue with ppoll() being stuck on my
> SMP machine: http://article.gmane.org/gmane.linux.file-systems/70414
OK, it doesn't fix my issue, but it seems to make it harder-to-hit...
> The change to sock_poll_wait() in
> commit 626cf236608505d376e4799adb4f7eb00a8594af
> (poll: add poll_requested_events() and poll_does_not_wait() functions)
> seems to have allowed additional cases where the SMP memory barrier
> is not issued before checking for readiness.
>
> In my case, this affects the select()-family of functions
> which register descriptors once and set _qproc to NULL before
> checking events again (after poll_schedule_timeout() returns).
> The set_mb() barrier in poll_schedule_timeout() appears to be
> insufficient on my SMP x86-64 machine (as it's only an xchg()).
>
> This may also be related to the epoll issue described by
> Andreas Voellmy in http://thread.gmane.org/gmane.linux.kernel/1408782/
However, I believe my patch will still fix Andreas' issue with epoll
due to how ep_modify() uses a NULL qproc when calling ->poll().
(I've never been able to reproduce Andreas' issue on my 4-core system,
but he's been hitting it since 3.4 (at least))
next prev parent reply other threads:[~2012-12-31 23:24 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 [this message]
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
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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