linux-kernel - Re: [PATCH 1/6] [2.6.29] epoll: fix for epoll_wait sometimes returning events on closed fds

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Date:	Tue, 24 Feb 2009 12:45:14 -0800 (PST)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Tony Battersby <tonyb@...ernetics.com>
cc:	Eric Dumazet <dada1@...mosbay.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] [2.6.29] epoll: fix for epoll_wait sometimes returning
 events on closed fds

On Tue, 24 Feb 2009, Tony Battersby wrote:

> Ugh.  The manpage on Ubuntu 8.04 that I am using doesn't contain this
> lengthy caveat; it just says "A6     Yes."  To me it sounds like the
> (newer) manpage is just documenting away a bug/misfeature with "It's
> supposed to do that.  Gives it character." rather than expecting the
> kernel developers to make the API behave in a more reasonable way.  Just
> my opinion; others may agree or disagree.
> 
> If the officially-sanctioned epoll interface is supposed to report
> events on fds that were added, duped, and then the original fd closed,
> then my patch will probably break that behavior.  In that case, it will
> be more difficult to fix problem that my patch is trying to fix (which
> doesn't involve dup, dup2, fcntl, fork, etc.).  So before I try to think
> of another way, let me ask: do we want to fix the problem that I am
> reporting, or just document it away in the manpage as (apparently) has
> been done before?

No. Like it has been explained, MT applications can report events for 
closed files anyway. It is a matter of where the close() happen in time 
(pretty easy to figure out if you make a time/thread chart).
As for the other patches, some could be applied, but I didn't look at them 
deeply and I need time to review them. Will take time to review them 
tomorrow or the day after.



- Davide


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