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Subject: Re: [PATCH 5/5] tracing: Do not record user stack trace from NMI
 context
From: Steven Rostedt <rostedt@goodmis.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Li Zefan <lizf@cn.fujitsu.com>, Lai Jiangshan <laijs@cn.fujitsu.com>,
       stable@kernel.org
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References: <20100313025655.104950166@goodmis.org>
	 <20100313025855.495916344@goodmis.org>  <20100314102747.GB5140@nowhere>
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Date: Sun, 14 Mar 2010 11:28:03 -0400
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On Sun, 2010-03-14 at 11:27 +0100, Frederic Weisbecker wrote:

> 
> Wow, that's a race :)
> 
> In perf this is dealt with a special copy_from_user_nmi()
> (see in arch/x86/kernel/cpu/perf_event.c)
> 
> May be save_stack_trace_user() should use that instead
> of a __copy_from_user_inatomic() based thing, just to
> cover such NMI corner race case.
> 

Yeah, we should move the __copy_from_user_nmi() out of the perf code and
into the normal uaccess code. Then we could do as you suggest, and have
the stack code do:

if (in_nmi())
	__copy_from_user_nmi();
else
	__copy_from_user_inatomic();

Or maybe it would be best to have the __copy_from_user_inatomic() handle
it.

-- Steve