linux-kernel - Re: pm-hibernate : possible circular locking dependency detected

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Message-ID: <20090409041746.GF20692@elte.hu>
Date:	Thu, 9 Apr 2009 06:17:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Ming Lei <tom.leiming@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Linux Kernel List <linux-kernel@...r.kernel.org>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: Re: pm-hibernate : possible circular locking dependency detected


* Rusty Russell <rusty@...tcorp.com.au> wrote:

> On Wednesday 08 April 2009 22:18:26 Peter Zijlstra wrote:
> > On Wed, 2009-04-08 at 12:47 +0930, Rusty Russell wrote:
> > > On Tuesday 07 April 2009 16:35:53 Peter Zijlstra wrote:
> > > > On Tue, 2009-04-07 at 13:56 +0930, Rusty Russell wrote:
> > > > > Looks like this will be fixed by Andrew's work-on-cpu-in-own-thread
> > > > > patch which I just put out the pull request for.
> > > > 
> > > > Would it make sense to teach it about a short-circuit like:
> > > > 
> > > > work_on_cpu() {
> > > > 
> > > >   if (cpumask_weight(current->cpus_allowed) == 1 && 
> > > >       smp_processor_id() == cpu)
> > > >     return do_work_right_here();
> > > 
> > > Does that happen much?  I guess put a counter in and see?
> > 
> > Ego spotted the case where cpufreq calls it from an cpu-affine
> > workqueue, it seems to me in that case its desirable to have the
> > short-cut, and currently that's needed for correctness too as it will
> > generate this circular lock thingy.
> 
> Well, the correctness issue is fixed by Andrew's 
> work_on_cpu-via-new-thread patch (hmm, which Linus hasn't taken, 
> re-xmitting).

That's now upstream as per:

 6b44003: work_on_cpu(): rewrite it to create a kernel thread on demand

So re-checking whether the warning still triggers with latest -git 
would be nice.

	Ingo
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