From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751346AbdHaBMf (ORCPT ); Wed, 30 Aug 2017 21:12:35 -0400 Received: from mail-qt0-f194.google.com ([209.85.216.194]:34618 "EHLO mail-qt0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750822AbdHaBMe (ORCPT ); Wed, 30 Aug 2017 21:12:34 -0400 Date: Wed, 30 Aug 2017 18:12:30 -0700 From: Tejun Heo To: Neeraj Upadhyay Cc: lizefan@huawei.com, mingo@kernel.org, longman@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, sramana@codeaurora.org, prsood@codeaurora.org Subject: Re: [PATCH] cgroup: Fix potential race between cgroup_exit and migrate path Message-ID: <20170831011230.GD491396@devbig577.frc2.facebook.com> References: <1504097649-32754-1-git-send-email-neeraju@codeaurora.org> <20170831005545.GA491396@devbig577.frc2.facebook.com> <20170831010319.GB491396@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170831010319.GB491396@devbig577.frc2.facebook.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 30, 2017 at 06:03:19PM -0700, Tejun Heo wrote: > Oops, more like the following. > > diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c > index df2e0f1..6f34025 100644 > --- a/kernel/cgroup/cgroup.c > +++ b/kernel/cgroup/cgroup.c > @@ -683,7 +683,7 @@ static void css_set_move_task(struct task_struct *task, > if (it->task_pos == &task->cg_list) > css_task_iter_advance(it); > > - list_del_init(&task->cg_list); > + list_del(&task->cg_list); > if (!css_set_populated(from_cset)) > css_set_update_populated(from_cset, false); > } else { > @@ -702,6 +702,8 @@ static void css_set_move_task(struct task_struct *task, > rcu_assign_pointer(task->cgroups, to_cset); > list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks : > &to_cset->tasks); > + } else { > + INIT_LIST_HEAD(&task->cg_list); > } > } On the third thought, I don't think this can happen either because now migration is strongly synchronized against exits. Please take a look at the changes around cgroup_threadgroup_rwsem. Thanks. -- tejun