linux-kernel - Re: Problem with freezable workqueues

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Message-ID: <20070228030113.GJ29179@in.ibm.com>
Date:	Wed, 28 Feb 2007 08:31:13 +0530
From:	Srivatsa Vaddagiri <vatsa@...ibm.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Pavel Machek <pavel@....cz>, Gautham R Shenoy <ego@...ibm.com>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>,
	Oleg Nesterov <oleg@...sign.ru>
Subject: Re: Problem with freezable workqueues

On Tue, Feb 27, 2007 at 10:51:27PM +0100, Rafael J. Wysocki wrote:
> We have a problem with freezable workqueues in 2.6.21-rc1 and in -mm
> (there are only two of them, in XFS, but still).  Namely, their worker threads
> deadlock with workqueue_cpu_callback() that gets called during the CPU hotplug,
> becuase workqueue_cpu_callback() tries to stop these threads while they are
> frozen (disable_nonboot_cpus() happens after we've frozen tasks).

This problem (of kthread_stopping a frozen thread) was there when we
implemented freezer-based cpu hotplug. We worked around that in the
callbacks by thawing the worker thread first before kthread_stopping it,
which is working pretty neatly.

Should that fix the issue? 

-- 
Regards,
vatsa
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