linux-kernel - Re: Problem with freezable workqueues

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Message-Id: <200702281840.40113.rjw@sisk.pl>
Date:	Wed, 28 Feb 2007 18:40:39 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	vatsa@...ibm.com
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 Wednesday, 28 February 2007 14:17, Srivatsa Vaddagiri wrote:
> 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?

Sure, I will.

> 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.

This one already is in -mm.
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