From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754570Ab1L1VHn (ORCPT ); Wed, 28 Dec 2011 16:07:43 -0500 Received: from mx1.redhat.com ([209.132.183.28]:11127 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754311Ab1L1VHl (ORCPT ); Wed, 28 Dec 2011 16:07:41 -0500 Message-ID: <4EFB850C.4030801@redhat.com> Date: Wed, 28 Dec 2011 22:07:24 +0100 From: Denys Vlasenko User-Agent: Mozilla/5.0 (X11; Linux i686; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: Denys Vlasenko CC: Tejun Heo , Oleg Nesterov , linux-kernel@vger.kernel.org, =?UTF-8?B?xYF1a2FzeiBNaWNoYWxpaw==?= , "Dmitry V. Levin" Subject: Re: Possible bug introduced in commit 9b84cca References: <201112281955.55200.vda.linux@googlemail.com> In-Reply-To: <201112281955.55200.vda.linux@googlemail.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/28/2011 07:55 PM, Denys Vlasenko wrote: > Hi Tejun, Oleg, > > Apologies if you are already informed about this bug > by people who originally discovered it. > > Looks like after commit 9b84cca, waitpid under strace > sometimes returns bogus ECHILD while child does exist. > > I did not yet confirm that the bug appeared exactly > at this commit - Łukasz says that. > > I confirmed that bug exists on kernels 3.1.6 (in Fedora) > and 3.1.0-rc4 (vanilla). I tested it under a few more Fedora kernels. On kernel-PAE-2.6.39-1.fc16.i686 bug does not trigger. On next Fedora kernel, kernel-PAE-3.0-0.rc1.git0.2.fc16.i686, it triggers. And indeed, these kernels differ in kernel/exit.c::wait_consider_task() only by commit 9b84cca. Oleg, if you need to test it, I have the setup on my machine. On Thu, Nov 17, 2011 at 10:25:26AM +0100, Łukasz Michalik wrote: > The bug only happens on recent linux. I've bisected the kernel and > found that it was introduced by 9b84cca2564b9 [2] in linux.git, so > pretty much everything since 3.0-rc2 is affected. Łukasz, looks like 3.0-rc1 is affected too. -- vda