Message-ID: <4B556118.7020502@cn.fujitsu.com>
Date: Tue, 19 Jan 2010 15:36:56 +0800
From: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Ingo Molnar <mingo@elte.hu>, Frederic Weisbecker <fweisbec@gmail.com>,
       Paul Mackerras <paulus@samba.org>, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 1/3] perf_event: fix race in perf_swevent_get_recursion_context()
References: <4B54654A.4090601@cn.fujitsu.com> <1263822958.4283.560.camel@laptop>
In-Reply-To: <1263822958.4283.560.camel@laptop>
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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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