From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f181.google.com (mail-we0-f181.google.com [74.125.82.181]) by kanga.kvack.org (Postfix) with ESMTP id B634B6B00DE for ; Mon, 9 Jun 2014 23:00:47 -0400 (EDT) Received: by mail-we0-f181.google.com with SMTP id q59so1429405wes.26 for ; Mon, 09 Jun 2014 20:00:47 -0700 (PDT) Received: from szxga02-in.huawei.com (szxga02-in.huawei.com. [119.145.14.65]) by mx.google.com with ESMTPS id fi1si14453554wib.89.2014.06.09.20.00.44 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 09 Jun 2014 20:00:46 -0700 (PDT) Message-ID: <53967465.7070908@huawei.com> Date: Tue, 10 Jun 2014 10:58:45 +0800 From: Li Zefan MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Gu Zheng , Andrew Morton , linux-kernel , Tejun Heo , linux-mm@kvack.org, Cgroups , stable@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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org