linux-kernel - Re: S06cpuspeed/2637 is trying to acquire lock (&(&dbs_info->work)->work (was: Re: [PATCH 4/6] x86/cpufreq: use cpumask

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Date:	Wed, 10 Jun 2009 16:58:48 -0400
From:	Dave Jones <davej@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Yinghai Lu <yinghai@...nel.org>, Avi Kivity <avi@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	cpufreq@...r.kernel.org, mark.langsdorf@....com
Subject: Re: S06cpuspeed/2637 is trying to acquire lock
	(&(&dbs_info->work)->work (was: Re: [PATCH 4/6] x86/cpufreq: use
	cpumask_copy instead of =)

On Wed, Jun 10, 2009 at 01:10:35PM +0200, Ingo Molnar wrote:
 > 
 > With a v2.6.30 based kernel i'm still getting a cpufreq lockdep 
 > warning:
 > 
 >  =======================================================
 >  [ INFO: possible circular locking dependency detected ]
 >  2.6.30-tip #10420
 >  -------------------------------------------------------
 >  S06cpuspeed/2637 is trying to acquire lock:
 >   (&(&dbs_info->work)->work){+.+...}, at: [<ffffffff8106553d>] __cancel_work_timer+0xd6/0x22a
 > 
 >  but task is already holding lock:
 >   (dbs_mutex){+.+.+.}, at: [<ffffffff8193d630>] cpufreq_governor_dbs+0x28f/0x335
 > 
 > This bug got introduced somewhere late in the .30-rc cycle, this box 
 > was fine before.

See the thread " [PATCH] remove rwsem lock from CPUFREQ_GOV_STOP call (second call site)" 
Though there's a report that the last patch posted still doesn't fix the problem,
so we still don't have a quick fix suitable for -stable.

It's this .. http://bugzilla.kernel.org/show_bug.cgi?id=13493
b14893a62c73af0eca414cfed505b8c09efc613c fixed one locking problem, but
introduced this as a side-effect.  The whole thing is a mess really.

	Dave

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