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

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Message-ID: <20090315174445.GD18305@kvack.org>
Date:	Sun, 15 Mar 2009 13:44:45 -0400
From:	Benjamin LaHaise <bcrl@...ck.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.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

On Sat, Mar 14, 2009 at 06:36:34PM -0700, Davide Libenzi wrote:
> 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 conceptually the bug is there.
> 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.

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.

		-ben
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