Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936247AbaFJDAy (ORCPT ); Mon, 9 Jun 2014 23:00:54 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:4447 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754382AbaFJDAw (ORCPT ); Mon, 9 Jun 2014 23:00:52 -0400 Message-ID: <53967465.7070908@huawei.com> Date: Tue, 10 Jun 2014 10:58:45 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: David Rientjes CC: Gu Zheng , Andrew Morton , linux-kernel , Tejun Heo , , Cgroups , Subject: Re: [PATCH] mm/mempolicy: fix sleeping function called from invalid context References: <53902A44.50005@cn.fujitsu.com> <20140605132339.ddf6df4a0cf5c14d17eb8691@linux-foundation.org> <539192F1.7050308@cn.fujitsu.com> <539574F1.2060701@cn.fujitsu.com> In-Reply-To: Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.18.230] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014/6/9 17:13, David Rientjes wrote: > 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. > Yes, this is a long-standing issue. Besides the race you described, the child task's mems_allowed can be wrong if the cpuset's nodemask changes before the child has been added to the cgroup's tasklist. I remember Tejun once said he wanted to disallow task migration between cgroups during fork, and that should fix this problem. >> 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? > Sounds you have other idea? -- 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/