Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753773AbZJVCDb (ORCPT ); Wed, 21 Oct 2009 22:03:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753536AbZJVCDb (ORCPT ); Wed, 21 Oct 2009 22:03:31 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:35664 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753485AbZJVCDa (ORCPT ); Wed, 21 Oct 2009 22:03:30 -0400 Date: Wed, 21 Oct 2009 19:00:28 -0700 From: Andrew Morton To: john stultz Cc: Arjan van de Ven , Andi Kleen , lkml , Mike Fulton , Sean Foley , Darren Hart Subject: Re: [RFC][PATCH] Add prctl to set sibling thread names Message-Id: <20091021190028.623a7f6e.akpm@linux-foundation.org> In-Reply-To: <1256172744.4768.22.camel@localhost.localdomain> References: <1256167297.4768.14.camel@localhost.localdomain> <20091021174804.3885db37@infradead.org> <1256172744.4768.22.camel@localhost.localdomain> X-Mailer: Sylpheed 2.4.7 (GTK+ 2.12.1; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1702 Lines: 45 On Wed, 21 Oct 2009 17:52:24 -0700 john stultz wrote: > On Wed, 2009-10-21 at 17:48 -0700, Arjan van de Ven wrote: > > On Wed, 21 Oct 2009 16:21:37 -0700 > > john stultz wrote: > > > > > > > > Taking a very raw attempt at this, I scratched out the following > > > simple implementation. I'd appreciate any review or suggestions for > > > improvements. I'm not at all certain the passing of the thread pid_t > > > through the unsigned long is valid, for instance, or if > > > same_thread_group() is the right check to make sure we only change > > > siblings and not tid from other processes. So any advice on better > > > approaches would be great. > > > > > > + return -EINVAL; > > > + > > > + set_task_comm(tsk, comm); > > > > > > you're pretty much the first now who touches ->comm from > > not-the-thread-itself.... are you sure that is safe? > > No, I'm not sure at all :) > > Thanks for pointing this out. I'll see whats needed in set_task_comm(). > set_task_comm() is OK. The problem will be the unwritten rule that processes can read *their own* ->comm without task_lock(), because nobody ever alters ->comm apart from tack which owns it. You've changed that, so all the open-coded accesses to current->comm are now racy. Also, you appear to be running set_task_comm() against a task_struct without holding a reference on that task. Will a well-timed exit() cause a modify-after-free? -- 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/