linux-kernel - Re: Failure to release lock after CPU hot-unplug canceled

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Date:	Tue, 9 Jan 2007 17:57:40 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Benjamin Gilbert <bgilbert@...cmu.edu>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Gautham shenoy <ego@...ibm.com>, Andrew Morton <akpm@...l.org>
Subject: Re: Failure to release lock after CPU hot-unplug canceled

On Tue, Jan 09, 2007 at 01:17:38PM +0100, Heiko Carstens wrote:
> missing in kernel cpu.c in _cpu_down() in case CPU_DOWN_PREPARE
> returned with NOTIFY_BAD. However... this reveals that there is just a
> more fundamental problem.
> 
> The workqueue code grabs a lock on CPU_[UP|DOWN]_PREPARE and releases it
> again on CPU_DOWN_FAILED/CPU_UP_CANCELED. If something in the callchain
> returns NOTIFY_BAD the rest of the entries in the callchain won't be
> called anymore. But DOWN_FAILED/UP_CANCELED will be called for every
> entry.
> So we might even end up with a mutex_unlock(&workqueue_mutex) even if
> mutex_lock(&workqueue_mutex) hasn't been called...

This is a known problem. Gautham had sent out patches to address them

http://lkml.org/lkml/2006/11/14/93

Looks like they are in latest mm tree. Perhaps the testcase should be
retried against latest mm.

-- 
Regards,
vatsa
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