linux-kernel - Re: [PATCH 01/12] rwsem: test for no active locks in __rwsem_do

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Date:	Wed, 12 May 2010 11:39:18 +0100
From:	David Howells <dhowells@...hat.com>
To:	Michel Lespinasse <walken@...gle.com>
Cc:	dhowells@...hat.com,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mike Waychison <mikew@...gle.com>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Ying Han <yinghan@...gle.com>
Subject: Re: [PATCH 01/12] rwsem: test for no active locks in __rwsem_do_wake undo code

Michel Lespinasse <walken@...gle.com> wrote:

> If there are no active threasd using a semaphore, it is always correct to
> unqueue blocked threads. This seems to be what was intended in the undo code.
> 
> What was done instead, was to look for a sem count of zero - this is an
> impossible situation, given that at least one thread is known to be queued
> on the semaphore. The code might be correct as written, but it's hard to
> reason about and it's not what was intended (otherwise the goto out would
> have been unconditional).
> 
> Go for checking the active count - the alternative is not worth the headache.

I think this is a definite bug fix, so I've sent it upstream in advance.

David
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