Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756665Ab1EQVzL (ORCPT ); Tue, 17 May 2011 17:55:11 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:43205 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751984Ab1EQVzJ convert rfc822-to-8bit (ORCPT ); Tue, 17 May 2011 17:55:09 -0400 Subject: Re: [PATCH 1/3] comm: Introduce comm_lock spinlock to protect task->comm access From: Peter Zijlstra To: Ingo Molnar Cc: John Stultz , LKML , Joe Perches , Michal Nazarewicz , Andy Whitcroft , Jiri Slaby , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org In-Reply-To: <20110517212734.GB28054@elte.hu> References: <1305665263-20933-1-git-send-email-john.stultz@linaro.org> <1305665263-20933-2-git-send-email-john.stultz@linaro.org> <20110517212734.GB28054@elte.hu> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Date: Tue, 17 May 2011 23:54:16 +0200 Message-ID: <1305669256.2466.6286.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.30.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1150 Lines: 26 On Tue, 2011-05-17 at 23:27 +0200, Ingo Molnar wrote: > * John Stultz wrote: > > > The implicit rules for current->comm access being safe without locking are no > > longer true. Accessing current->comm without holding the task lock may result > > in null or incomplete strings (however, access won't run off the end of the > > string). > > This is rather unfortunate - task->comm is used in a number of performance > critical codepaths such as tracing. > > Why does this matter so much? A NULL string is not a big deal. > > Note, since task->comm is 16 bytes there's the CMPXCHG16B instruction on x86 > which could be used to update it atomically, should atomicity really be > desired. The changelog also fails to mention _WHY_ this is no longer true. Nor does it treat why making it true again isn't an option. Who is changing another task's comm? That's just silly. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/