From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755532Ab1IHXcl (ORCPT ); Thu, 8 Sep 2011 19:32:41 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40468 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754596Ab1IHXcg (ORCPT ); Thu, 8 Sep 2011 19:32:36 -0400 Date: Thu, 8 Sep 2011 23:31:30 +0200 From: Oleg Nesterov To: Ben Blum Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, fweisbec@gmail.com, neilb@suse.de, paul@paulmenage.org, paulmck@linux.vnet.ibm.com Subject: Re: + cgroups-more-safe-tasklist-locking-in-cgroup_attach_proc.patch added to -mm tree Message-ID: <20110908213130.GA3924@redhat.com> References: <201109012108.p81L8X0b029484@imap1.linux-foundation.org> <20110902123706.GB26764@redhat.com> <20110902140015.GA31530@redhat.com> <20110902141550.GA24012@unix33.andrew.cmu.edu> <20110902155534.GA4595@redhat.com> <20110907235931.GA22545@unix33.andrew.cmu.edu> <20110908173559.GA26492@redhat.com> <20110908185805.GB15434@ghc03.ghc.andrew.cmu.edu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110908185805.GB15434@ghc03.ghc.andrew.cmu.edu> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/08, Ben Blum wrote: > > As for the patch below (which is the same as it was last time?): It is the same, yes, I simply copied it from my old email. BTW, it wasn't tested at all, even compiled. > did you > mean for Andrew to replace the old tasklist_lock patch with this one, or > should one of us rewrite this against it? This is up to you. And just in case, please feel free to do nothing and keep the current fix. > either way, it should have > something like the comment I proposed in the first thread. Confused... Aha, I missed another email from you. You mean /* If the leader exits, its links on the thread_group list become * invalid. One way this can happen is if a sub-thread does exec() when * de_thread() calls release_task(leader) (and leader->sighand gets set * to NULL, in which case lock_task_sighand will fail). Since in that * case the threadgroup is still around, cgroup_procs_write should try * again (finding the new leader), which EAGAIN indicates here. This is * "double-double-toil-and-trouble-check locking". */ Agreed. Off-topic question... Looking at this code, it seems that attach_task_by_pid(zombie_pid, threadgroup => true) returns 0. single-task-only case fails with -ESRCH in this case. I am not saying this is wrong, just this looks a bit strange (unless I misread the code). Oleg.