linux-kernel - Re: [LKP] [sched] BUG: kernel boot hang

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Message-ID: <20150216150733.GD5029@twins.programming.kicks-ass.net>
Date:	Mon, 16 Feb 2015 16:07:33 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Huang Ying <ying.huang@...el.com>,
	Ingo Molnar <mingo@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>, LKP ML <lkp@...org>
Subject: Re: [LKP] [sched] BUG: kernel boot hang

On Sun, Feb 15, 2015 at 01:18:07PM -0500, Steven Rostedt wrote:
> On Sun, 15 Feb 2015 16:46:22 +0100
> Frederic Weisbecker <fweisbec@...il.com> wrote:
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index c017a5f..a6d4d6c 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -2879,7 +2879,7 @@ void __sched schedule_preempt_disabled(void)
> >  	preempt_disable();
> >  }
> >  
> > -static void preempt_schedule_common(void)
> > +static void __sched notrace preempt_schedule_common(void)
> >  {
> >  	do {
> >  		preempt_count_add(PREEMPT_ACTIVE);
> 
> Ah, since I added better recursion protection code in function tracer
> this didn't break that. But unfortunately, function graph tracer
> doesn't have that protection.
> 
> If it traces between preempt_schedule() and where it sets
> PREEMPT_ACTIVE, it can indeed go into an infinite recursion. Yeah,
> preempt_schedule_common() should be notrace, at least until we change
> function_graph to have that recursion protection.
> 
> Acked-by: Steven Rostedt <rostedt@...dmis.org>


Can someone shoot me a proper patch with Changelog and such?
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