linux-kernel - Re: [BUG] perf: hard lockup when using perf-sched

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Date:	Fri, 26 Mar 2010 18:23:54 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Mike Galbraith <efault@....de>
Cc:	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Paul Mackerras <paulus@...ba.org>
Subject: Re: [BUG] perf: hard lockup when using perf-sched

On Fri, Mar 26, 2010 at 11:11:33AM +0100, Mike Galbraith wrote:
> On Thu, 2010-03-25 at 10:27 +0100, Mike Galbraith wrote:
> > On Thu, 2010-03-25 at 16:04 +0800, Li Zefan wrote:
> > > Mike Galbraith wrote:
> > > > On Wed, 2010-03-24 at 08:32 +0100, Mike Galbraith wrote:
> > > > 
> > > >> I just saw this, hunted down your testcase and tried it here.  Looks
> > > >> like perf_output_lock() wedged box.
> > > > 
> > > > (turns on frame pointers, and adds noinline)
> > > > 
> > > 
> > > Thanks! Then who's going to fix this...
> > 
> > Well, that kinda depends on whether I figure out how the heck it's all
> > supposed to work before somebody else whacks it or not.
> 
> This seems to work, in contrast to everything I tried yesterday.  Not
> exactly a thing of beauty, but at least it's an option, so...
> 
> perf: fix perf sched record forkbomb deadlock
> 
> perf sched record can deadlock a box should the holder of handle->data->lock
> take an interrupt, and then attempt to acquire an rq lock held by a CPU trying
> to acquire the same lock.  Disable interrupts.



Aah.

So the scenario is the following inversion?

	CPU0				CPU1
sched event with rq->lock held
				grab handle->data->lock
spin on handle->data->lock
				interrupt
				try to grab rq->lock

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