From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752446Ab1LTTBh (ORCPT ); Tue, 20 Dec 2011 14:01:37 -0500 Received: from mail-qy0-f174.google.com ([209.85.216.174]:33149 "EHLO mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752374Ab1LTTBW (ORCPT ); Tue, 20 Dec 2011 14:01:22 -0500 From: Frederic Weisbecker To: Tejun Heo , Li Zefan Cc: LKML , Frederic Weisbecker , Containers , Cgroups , KAMEZAWA Hiroyuki , Oleg Nesterov , Andrew Morton , Paul Menage , Mandeep Singh Baines Subject: [PATCH 2/2] cgroup: Drop task_lock(parent) on cgroup_fork() Date: Tue, 20 Dec 2011 20:01:13 +0100 Message-Id: <1324407673-18975-2-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1324407673-18975-1-git-send-email-fweisbec@gmail.com> References: <1324320274-18485-1-git-send-email-msb@chromium.org> <1324407673-18975-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We don't need to hold the parent task_lock() on the parent in cgroup_fork() because we are already synchronized against the two places that may change the parent css_set concurrently: - cgroup_exit(), but the parent obviously can't exit concurrently - cgroup migration: we are synchronized against threadgroup_lock() So we can safely remove the task_lock() there. Signed-off-by: Frederic Weisbecker Cc: Tejun Heo Cc: Li Zefan Cc: Containers Cc: Cgroups Cc: KAMEZAWA Hiroyuki Cc: Oleg Nesterov Cc: Andrew Morton Cc: Paul Menage Cc: Mandeep Singh Baines --- kernel/cgroup.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 6b5f693..a1e87a4 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4544,7 +4544,7 @@ static const struct file_operations proc_cgroupstats_operations = { * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since - * it was not made under the protection of RCU or cgroup_mutex, so + * it was not made under the protection of threadgroup_change_begin(), so * might no longer be a valid cgroup pointer. cgroup_attach_task() might * have already changed current->cgroups, allowing the previously * referenced cgroup group to be removed and freed. @@ -4554,10 +4554,14 @@ static const struct file_operations proc_cgroupstats_operations = { */ void cgroup_fork(struct task_struct *child) { - task_lock(current); + /* + * We don't need to task_lock() current because current->cgroups + * can't be changed concurrently here. The parent obviously hasn't + * exited and called cgroup_exit(), and we are synchronized against + * cgroup migration through threadgroup_change_begin(). + */ child->cgroups = current->cgroups; get_css_set(child->cgroups); - task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } -- 1.7.5.4