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Date: Wed, 17 Mar 2010 03:08:01 +0100
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
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
Subject: Re: [PATCH 5/5] tracing: Do not record user stack trace from NMI
	context
Message-ID: <20100317020759.GE5258@nowhere>
References: <20100313025655.104950166@goodmis.org> <20100313025855.495916344@goodmis.org> <20100314102747.GB5140@nowhere> <1268585920.13400.14.camel@localhost>
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On Sun, Mar 14, 2010 at 12:58:40PM -0400, Steven Rostedt wrote:
> 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.


Yeah, agreed.