linux-kernel - Re: [PATCH wq#for-next] workqueue: fix how cpu number is stored in work->data

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Date:	Thu, 22 Jul 2010 17:10:28 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Sachin Sant <sachinp@...ibm.com>, linux-s390@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>
Subject: Re: [PATCH wq#for-next] workqueue: fix how cpu number is stored in
 work->data

On Thu, 22 Jul 2010 14:25:28 +0200
Tejun Heo <tj@...nel.org> wrote:

> Once a work starts execution, its data contains the cpu number it was
> on instead of pointing to cwq.  This is added by commit 7a22ad75
> (workqueue: carry cpu number in work data once execution starts) to
> reliably determine the work was last on even if the workqueue itself
> was destroyed inbetween.
> 
> Whether data points to a cwq or contains a cpu number was
> distinguished by comparing the value against PAGE_OFFSET.  The
> assumption was that a cpu number should be below PAGE_OFFSET while a
> pointer to cwq should be above it.  However, on architectures which
> use separate address spaces for user and kernel spaces, this doesn't
> hold as PAGE_OFFSET is zero.
> 
> Fix it by using an explicit flag, WORK_STRUCT_CWQ, to mark what the
> data field contains.  If the flag is set, it's pointing to a cwq;
> otherwise, it contains a cpu number.
> 
> Reported on s390 and microblaze during linux-next testing.
> 
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Reported-by: Sachin Sant <sachinp@...ibm.com>
> Reported-by: Michal Simek <michal.simek@...alogix.com>
> Reported-by: Martin Schwidefsky <schwidefsky@...ibm.com>
> ---
> Yeah, that was a stupid assumption by me.  Can you guys please test
> whether this fixes the problem?

Compiles and boots for s390. Thanks.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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