linux-kernel - Re: [patch] eventfd/kaio integration fix

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Message-ID: <Pine.LNX.4.64.0804091217150.7000@alien.or.mcafeemobile.com>
Date:	Wed, 9 Apr 2008 12:19:50 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	zach.brown@...cle.com, jroberson@...sapeake.net
Subject: Re: [patch] eventfd/kaio integration fix

On Wed, 9 Apr 2008, Andrew Morton wrote:

> On Wed, 9 Apr 2008 11:45:47 -0700 (PDT)
> Davide Libenzi <davidel@...ilserver.org> wrote:
> 
> > Jeff Roberson discovered a race when using kaio eventfd based 
> > notifications. This patch fixes the race by moving the notification inside 
> > the spinlocked section of kaio.
> 
> Missing information.
> 
> What are the consequences of this race, when it occurs?

This was described in the original email. I posted a patch back then 
(waiting for Jeff test feedback - that never came), but then I forgot 
about it till now:

http://groups.google.com/group/linux.kernel/browse_thread/thread/e814b54c14198616



> > The operation is safe since eventfd 
> > spinlock and kaio one are unrelated.
> 
> Yes, it's safe from that perspective.
> 
> However with this patch applied, we will no longer run eventfd_signal() if
> kiocbIsCancelled(iocb).  Convincing is needed, please?

This was the intended behaviour. No event was actually *ready*, so no need 
to signal completion of an event.



- Davide


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