linux-kernel - Re: 2.6.22-rc1: Broken suspend on SMP with tifm

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Message-Id: <200705132350.32582.rjw@sisk.pl>
Date:	Sun, 13 May 2007 23:50:31 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Alex Dubov <oakad@...oo.com>, Pierre Ossman <drzeus@...eus.cx>
Subject: Re: 2.6.22-rc1: Broken suspend on SMP with tifm

On Sunday, 13 May 2007 23:34, Oleg Nesterov wrote:
> On 05/13, Rafael J. Wysocki wrote:
> >
> > > > On Sunday, 13 May 2007 22:30, Oleg Nesterov wrote:
> > > > >
> > > > > I think the better fix (at least for now) is
> > > > > 
> > > > > 	- #define create_freezeable_workqueue(name) __create_workqueue((name), 0, 1)
> > > > > 	+ #define create_freezeable_workqueue(name) __create_workqueue((name), 1, 1)
> > > > > 
> > > > > Alex, do you really need a multithreaded wq?
> > > > > 
> > > > > Rafael, what do you think?
> > > > 
> > Sure, if a singlethread workqueue is sufficient for Alex, I agree that this
> > would be preferable.
> 
> Great. Alex?
> 
> > @@ -819,20 +843,31 @@ static int __devinit workqueue_cpu_callb
> >  
> > +
> > +		case CPU_DEAD_FROZEN:
> > +			if (wq->freezeable) {
> > +				take_over_work(wq, cpu);
> > +				thaw_process(cwq->thread);
> 
> Suppose that PF_NOFREEZE task T does flush_workqueue(), and CPU 1 has pending
> works. T does flush_cpu_workqueue(0), CPU_DEAD_FROZEN moves works from CPU 1
> to CPU 0, T does flush_cpu_workqueue(1) and finds nothing.

I don't think this is possible, because we've acquired workqueue_mutex in
_cpu_down().

Greetings,
Rafael
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