Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933446AbaFIJOH (ORCPT ); Mon, 9 Jun 2014 05:14:07 -0400 Received: from mail-ig0-f179.google.com ([209.85.213.179]:37869 "EHLO mail-ig0-f179.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932579AbaFIJOA (ORCPT ); Mon, 9 Jun 2014 05:14:00 -0400 Date: Mon, 9 Jun 2014 02:13:57 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Gu Zheng cc: Andrew Morton , linux-kernel , Tejun Heo , linux-mm@kvack.org, Cgroups , stable@vger.kernel.org, Li Zefan Subject: Re: [PATCH] mm/mempolicy: fix sleeping function called from invalid context In-Reply-To: <539574F1.2060701@cn.fujitsu.com> Message-ID: References: <53902A44.50005@cn.fujitsu.com> <20140605132339.ddf6df4a0cf5c14d17eb8691@linux-foundation.org> <539192F1.7050308@cn.fujitsu.com> <539574F1.2060701@cn.fujitsu.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 9 Jun 2014, Gu Zheng wrote: > > I think your patch addresses the problem that you're reporting but misses > > the larger problem with cpuset.mems rebinding on fork(). When the > > forker's task_struct is duplicated (which includes ->mems_allowed) and it > > races with an update to cpuset_being_rebound in update_tasks_nodemask() > > then the task's mems_allowed doesn't get updated. > > Yes, you are right, this patch just wants to address the bug reported above. > The race condition you mentioned above inherently exists there, but it is yet > another issue, the rcu lock here makes no sense to it, and I think we need > additional sync-mechanisms if want to fix it. Yes, the rcu lock is not providing protection for any critical section here that requires (1) the forker's cpuset to be stored in cpuset_being_rebound or (2) the forked thread's cpuset to be rebound by the cpuset nodemask update, and no race involving the two. > But thinking more, though the current implementation has flaw, but I worry > about the negative effect if we really want to fix it. Or maybe the fear > is unnecessary.:) > It needs to be slightly rewritten to work properly without negatively impacting the latency of fork(). Do you have the cycles to do it? -- 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/