linux-kernel - Re: Problem with freezable workqueues

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Date:	Wed, 28 Feb 2007 18:47:21 +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 Wed, Feb 28, 2007 at 12:11:03PM +0100, Rafael J. Wysocki wrote:
> > In addition to thawing worker thread before kthread_stopping it, there
> > are minor changes required in worker threads, to check for
> > is_cpu_offline(bind_cpu) when they come out of refrigerator and jump to
> > wait_to_die if so (ex: softirq.c).
> > 
> > I guess you would need these changes before freezer-based hotplug is
> > merged, in which case Gautham can send those patches out first.
> 
> Yes, please, if that's possible.

After looking at the current workqueue code, the above minor change I
suggested is not required.

So you should be able to fix your "kthread_stop on a frozen worker
thread hangs" problem by just a simple patch like this (against
2.6.20-mm2):


--- workqueue.c.org	2007-02-28 18:32:48.000000000 +0530
+++ workqueue.c	2007-02-28 18:44:23.000000000 +0530
@@ -718,6 +718,8 @@ static void cleanup_workqueue_thread(str
 		insert_wq_barrier(cwq, &barr, 1);
 		cwq->should_stop = 1;
 		alive = 1;
+		if (frozen(cwq->thread))
+			thaw(cwq->thread);
 	}
 	spin_unlock_irq(&cwq->lock);
 

Can you test with this?

Note that as Oleg commented, freezable workqueues are broken w/o his
patch here:

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

So you need to have Andrew/Linux pick up the above patch first to have
correctly functioning freezable workqueues.

-- 
Regards,
vatsa
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