linux-kernel - Re: [PATCH 5/5] tracing: Do not record user stack trace from NMI context

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Date:	Sun, 14 Mar 2010 12:58:40 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Li Zefan <lizf@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>, stable@...nel.org
Subject: Re: [PATCH 5/5] tracing: Do not record user stack trace from NMI
 context

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



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