linux-kernel - Re: [RFC][PATCH] kprobes: Add separate preempt

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Date:	Fri, 01 Jul 2011 22:15:05 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC][PATCH] kprobes: Add separate preempt_disabling for kprobes

(2011/07/01 21:19), Steven Rostedt wrote:
> On Fri, 2011-07-01 at 14:09 +0900, Masami Hiramatsu wrote:
> 
>> BTW, on my tip tree, add_preempt_count (a.k.a. inc_preempt_count())
>> is marked as __kprobes, so it can not be probed. Is there any change?
>>
> 
> That is when debug or preempt tracer is enabled. Otherwise it's
> hardcoded into whatever calls it:
> 
> #if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
>   extern void add_preempt_count(int val);
>   extern void sub_preempt_count(int val);
> #else
> # define add_preempt_count(val)	do { preempt_count() += (val); } while (0)
> # define sub_preempt_count(val)	do { preempt_count() -= (val); } while (0)
> #endif
> 
> 
> Anyway, it still doesn't help the place that reads preempt_count() and
> then later uses the result. I hit the crash in schedule_bug() where it
> increments preempt count, then reads it to see if it is only 1.

Ah, I see, that what I need...
I've made a fix patch for that, so could you test that?

Thank you,

-- 
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com
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