linux-kernel - Re: [PATCH][GIT PULL] tracing: Fix compile issue for trace_sched

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Date:	Thu, 21 Oct 2010 11:58:56 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	2nddept-manager@....hitachi.co.jp
Subject: Re: [PATCH][GIT PULL] tracing: Fix compile issue for	trace_sched_wakeup.c

(2010/10/21 1:43), Jason Baron wrote:
> On Wed, Oct 20, 2010 at 05:40:45PM +0200, Ingo Molnar wrote:
>> FYI, there's a new mystery hang (sometimes crash) that triggers in -tip - and which 
>> seems to be tracing related. See the crashlog below - config attached.
>>
>> It's not bisectable - small changes in the kernel make the bug come/go. (might be a 
>> race of some sorts)
>>
>> Thanks,
>>
>> 	Ingo
>>
> 
> strange b/c it looks like we get though enabling/disabling the
> tracepoitns individually, but then when we go to enable all the
> tracepoints we hit this hang - perhaps, suggesting a race. Do we always
> fail after "Testing all events:" is printed? Does the crash have any
> more clues. I will try and re-produce this.
> 
> Also, I noticed some recent changes to text_poke_smp() usage of
> stop_machine() on Oct. 14th. That's related to the area where this appears
> to hang, so if things were working with this .config before then, that
> might be a place to look. Adding Masami to the 'cc list.

Recent changes of text_poke_smp() just removed unnecessary
get/put_online_cpu(), so I think it's not related this bug.

It seems there can be a bug in stop_machine() routine under
heavy use. usually that is called just once at a time, but jump
label and optprobe might call it heavily (thousands times?).
So some racy situation can be happen easily.

Thanks,

> 
> thanks,
> 
> -Jason
> --
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-- 
Masami HIRAMATSU
2nd Dept. Linux Technology Center
Hitachi, Ltd., Systems Development Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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