linux-kernel - Re: [PATCH] epoll: prevent missed events on EPOLL_CTL

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Message-ID: <20130102211632.GB17806@dcvr.yhbt.net>
Date:	Wed, 2 Jan 2013 21:16:32 +0000
From:	Eric Wong <normalperson@...t.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hans Verkuil <hans.verkuil@...co.com>,
	Jiri Olsa <jolsa@...hat.com>, Jonathan Corbet <corbet@....net>,
	Al Viro <viro@...iv.linux.org.uk>,
	Davide Libenzi <davidel@...ilserver.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	David Miller <davem@...emloft.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andreas Voellmy <andreas.voellmy@...e.edu>,
	"Junchang(Jason) Wang" <junchang.wang@...e.edu>,
	Network Development <netdev@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] epoll: prevent missed events on EPOLL_CTL_MOD

Eric Wong <normalperson@...t.net> wrote:
> Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> > Please document the barrier that this mb() pairs with, and then give
> > an explanation for the fix in the commit message, and I'll happily
> > take it. Even if it's just duplicating the comments above the
> > wq_has_sleeper() function, except modified for the ep_modify() case.
> 
> Hopefully my explanation is correct and makes sense below,
> I think both effects of the barrier are needed

I noticed Linus accepted this already.  This should probably go to
stable, right?

>From ancient git history[1], it seems this bug exists for all
2.6 kernels:

	commit 424980a87e226d63af46579b2af16ec1b8d17e52
	Author: Davide Libenzi <davidel@...ilserver.org>
	Date:   Thu Nov 14 16:17:23 2002 -0800

	    [PATCH] epoll bits 0.46 ...

[1] - git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git
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