linux-kernel - Re: [PATCH] make cancel_rearming_delayed

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Message-ID: <20070513212548.GA3185@tv-sign.ru>
Date:	Mon, 14 May 2007 01:25:48 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Tejun Heo <htejun@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Chinner <dgc@....com>,
	David Howells <dhowells@...hat.com>,
	Gautham Shenoy <ego@...ibm.com>,
	Jarek Poplawski <jarkao2@...pl>, Ingo Molnar <mingo@...e.hu>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] make cancel_rearming_delayed_work() reliable

Hi Tejun,

Sorry, I can't give a "complete" reply today (will do tomorrow),
just one note right now...

On 05/13, Tejun Heo wrote:
> 
> Oleg Nesterov wrote:
> >> * try_to_grab_pending() checks VALID && pointers equal after grabbing
> >> cwq->lock.
> > 
> > We don't even need to check the pointers. VALID bit is always changed
> > under cwq->lock. So, if we see VALID under cwq->lock, we have a right
> > pointer.
> 
> But there are multiple cwq->lock's.  VALID can be set with one of other
> cwq->lock's locked.

Oops. Thanks for correcting me. _This_ was a reson for a stupid barrier!

Oleg.

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