From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759535Ab0CNQ6n (ORCPT ); Sun, 14 Mar 2010 12:58:43 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.124]:35111 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753530Ab0CNQ6m (ORCPT ); Sun, 14 Mar 2010 12:58:42 -0400 X-Authority-Analysis: v=1.0 c=1 a=pnHbx7LlBzgA:10 a=IkcTkHD0fZMA:10 a=zUv7YOsU7YJl4P8mGsMA:9 a=oWdcjAXW-CPajTmz0ub4ldDtab4A:4 a=QEXdDO2ut3YA:10 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.89.75 Subject: Re: [PATCH 5/5] tracing: Do not record user stack trace from NMI context From: Steven Rostedt To: Frederic Weisbecker Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Li Zefan , Lai Jiangshan , stable@kernel.org In-Reply-To: <20100314102747.GB5140@nowhere> References: <20100313025655.104950166@goodmis.org> <20100313025855.495916344@goodmis.org> <20100314102747.GB5140@nowhere> Content-Type: text/plain; charset="UTF-8" Date: Sun, 14 Mar 2010 12:58:40 -0400 Message-ID: <1268585920.13400.14.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.28.2 (2.28.2-1.fc12) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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