linux-kernel - Re: Problem with freezable workqueues

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Message-ID: <20070228084859.GB104@tv-sign.ru>
Date:	Wed, 28 Feb 2007 11:48:59 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Gautham R Shenoy <ego@...ibm.com>,
	Johannes Berg <johannes@...solutions.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Problem with freezable workqueues

On 02/28, Srivatsa Vaddagiri wrote:
>
> On Wed, Feb 28, 2007 at 12:57:35AM +0100, Rafael J. Wysocki wrote:
> > > How about other kthread_stop()s ? For example, kernel/softirq.c:cpu_callback() ?
> > 
> > They all are PF_NOFREEZE, I suppose.  If we make all workqueues nonfreezable
> > (as they were before), the problem won't appear.
> 
> We can just thaw the worker thread selectively before kthread_stopping
> them. This will let us freeze all worker threads (which we want to for
> hotplug anyway).

I am not sure this is a good change for 2.6.21.

I strongly believe it is better to change XFS so that it doesn't use
create_freezeable_workqueue() as Rafael suggested. Besides, freezeable
workqueues are buggy anyway in 2.6.21-rc,

	http://marc.theaimsgroup.com/?l=linux-kernel&m=116855740612755

This means that workqueues become non-freezeable after suspend/resume
anyway (if I understand disable_nonboot_cpus() correctly).

Oleg.

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