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

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Date:	Tue, 19 Jan 2010 09:41:03 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
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()

On Tue, 2010-01-19 at 15:36 +0800, Xiao Guangrong wrote:
> 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

Still its not going to happen, we need those 4 recursion contexts.
Otherwise we could not receive a software event from an IRQ while we are
processing a software event from process context, etc.

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