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

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Message-Id: <200705140021.14129.rjw@sisk.pl>
Date:	Mon, 14 May 2007 00:21:13 +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 23:54, Oleg Nesterov wrote:
> On 05/13, Rafael J. Wysocki wrote:
> >
> > On Sunday, 13 May 2007 23:34, Oleg Nesterov wrote:
> > > On 05/13, Rafael J. Wysocki wrote:
> > > >
> > > > @@ -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().
> 
> Yes, we did... but flush_workqueue() doesn't take it?

I was looking at the 2.6.21 code, sorry.

Hmm, I guess we could add an additional mutex that would only be taken in
flush_workqueue() and in _cpu_down()/_cpu_up() via workqueue_cpu_callback()
with CPU_LOCK_ACQUIRE?

It doesn't seem to be a good idea to run flush_workqueue() while CPUs are being
taken up and down anyway.

Greetings,
Rafael
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