From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755934AbaCYRlL (ORCPT ); Tue, 25 Mar 2014 13:41:11 -0400 Received: from youngberry.canonical.com ([91.189.89.112]:55888 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755001AbaCYRVc (ORCPT ); Tue, 25 Mar 2014 13:21:32 -0400 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Tejun Heo , Kamal Mostafa Subject: [PATCH 3.8 40/81] cgroup: update cgroup_enable_task_cg_lists() to grab siglock Date: Tue, 25 Mar 2014 10:15:53 -0700 Message-Id: <1395767794-5012-41-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.8.3.2 In-Reply-To: <1395767794-5012-1-git-send-email-kamal@canonical.com> References: <1395767794-5012-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.8.13.20 -stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit 532de3fc72adc2a6525c4d53c07bf81e1732083d upstream. Currently, there's nothing preventing cgroup_enable_task_cg_lists() from missing set PF_EXITING and race against cgroup_exit(). Depending on the timing, cgroup_exit() may finish with the task still linked on css_set leading to list corruption. Fix it by grabbing siglock in cgroup_enable_task_cg_lists() so that PF_EXITING is guaranteed to be visible. This whole on-demand cg_list optimization is extremely fragile and has ample possibility to lead to bugs which can cause things like once-a-year oops during boot. I'm wondering whether the better approach would be just adding "cgroup_disable=all" handling which disables the whole cgroup rather than tempting fate with this on-demand craziness. Signed-off-by: Tejun Heo Acked-by: Li Zefan Signed-off-by: Kamal Mostafa --- kernel/cgroup.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index ba9e28c..a2d2c80 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -2982,9 +2982,14 @@ static void cgroup_enable_task_cg_lists(void) * We should check if the process is exiting, otherwise * it will race with cgroup_exit() in that the list * entry won't be deleted though the process has exited. + * Do it while holding siglock so that we don't end up + * racing against cgroup_exit(). */ + spin_lock_irq(&p->sighand->siglock); if (!(p->flags & PF_EXITING) && list_empty(&p->cg_list)) list_add(&p->cg_list, &p->cgroups->tasks); + spin_unlock_irq(&p->sighand->siglock); + task_unlock(p); } while_each_thread(g, p); read_unlock(&tasklist_lock); -- 1.8.3.2