linux-kernel - Re: [patch] eventfd - remove fput() call from possible IRQ context (3rd rev)

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Message-ID: <x493adahh0i.fsf@segfault.boston.devel.redhat.com>
Date:	Wed, 18 Mar 2009 13:34:21 -0400
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Benjamin LaHaise <bcrl@...ck.org>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>,
	linux-aio <linux-aio@...ck.org>, zach.brown@...cle.com
Subject: Re: [patch] eventfd - remove fput() call from possible IRQ context (3rd rev)

Davide Libenzi <davidel@...ilserver.org> writes:

> The following patch remove a possible source of fput() call from inside 
> IRQ context. Myself, like Eric, wasn't able to reproduce an fput() call 
> from IRQ context, but Jeff said he was able to, with the attached test 
> program. Independently from this, the bug is conceptually there, so we 
> might be better off fixing it.
> This patch adds an optimization similar to the one we already do on 
> ->ki_filp, on ->ki_eventfd. Playing with ->f_count directly is not pretty 
> in general, but the alternative here would be to add a brand new delayed 
> fput() infrastructure, that I'm not sure is worth it.
>
>
> On Sun, 15 Mar 2009, Benjamin LaHaise wrote:
>
>> This looks reasonably sane, the only concern I have with it is that I think 
>> it logically makes more sense to use the same convention for fi_filp and 
>> ki_eventfd, as the different in IS_ERR vs checking for NULL is a bit 
>> confusing.  Aside from that, it looks like it should fix the problem 
>> correctly.
>
> Makes sense.
>
>
>
> Signed-off-by: Davide Libenzi <davidel@...ilserver.org>

Signed-off-by: Jeff Moyer <jmoyer@...hat.com>
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