linux-kernel - Re: [PATCH 1/3] perf_event: fix race in perf_swevent_get_recursion

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Message-ID: <4B556118.7020502@cn.fujitsu.com>
Date:	Tue, 19 Jan 2010 15:36:56 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] perf_event: fix race in perf_swevent_get_recursion_context()

Hi Peter,

Peter Zijlstra wrote:
> On Mon, 2010-01-18 at 21:42 +0800, Xiao Guangrong wrote:
>> It only disable preemption in perf_swevent_get_recursion_context()
>> it can't avoid race of hard-irq and NMI
>>
>> In this patch, we use atomic operation to avoid it and reduce
>> cpu_ctx->recursion size, it also make this patch no need diable
>> preemption
> 
> Uhm why?
> 
> This patch looks terminally broken

Please see my explanation in another mail:
http://lkml.org/lkml/2010/1/18/501

Thanks,
Xiao
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