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

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Message-ID: <20080409093150.P43186@desktop>
Date:	Wed, 9 Apr 2008 09:33:00 -1000 (HST)
From:	Jeff Roberson <jroberson@...berson.net>
To:	Davide Libenzi <davidel@...ilserver.org>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	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, Davide Libenzi wrote:

> 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
>

I was thinking about stirring this up again myself.  Testing was 
complicated by several factors.  None of them related to this patch. 
However, I feel confident that this has solved our issue.

Jeff

>
>
>>> 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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