linux-kernel - Re: 2.6.35-rc3 deadlocks on semaphore operations

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Message-ID: <AANLkTimE_BeA3yiCovC0ckn_MbbH3lpgctLD8zD5ir6j@mail.gmail.com>
Date:	Wed, 23 Jun 2010 21:14:22 +0200
From:	Luca Tettamanti <kronos.it@...il.com>
To:	Manfred Spraul <manfred@...orfullife.com>
Cc:	Christoph Lameter <cl@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Julia Lawall <julia@...u.dk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	maciej.rutecki@...il.com
Subject: Re: 2.6.35-rc3 deadlocks on semaphore operations

On Wed, Jun 23, 2010 at 6:29 PM, Manfred Spraul
<manfred@...orfullife.com> wrote:
> Hi,
>
> I think I found it:
> Previously, queue.status was never IN_WAKEUP when the semaphore spinlock was
> held.
>
> The last patch changes that:
> Now the change from IN_WAKEUP to the final result code happens after the the
> semaphore spinlock is dropped.
> Thus a task can observe IN_WAKEUP even when it acquired the semaphore
> spinlock.
>
> As a result, semop() sometimes returned 1 (IN_WAKEUP) for a successful
> operation.
>
> Attached is a patch that should fix the bug.

Apache seems fine.

Tested-by: Luca Tettamanti <kronos.it@...il.com>

thanks,
Luca
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