From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754861AbaKDQJA (ORCPT ); Tue, 4 Nov 2014 11:09:00 -0500 Received: from terminus.zytor.com ([198.137.202.10]:59381 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754237AbaKDQIx (ORCPT ); Tue, 4 Nov 2014 11:08:53 -0500 Date: Tue, 4 Nov 2014 08:07:37 -0800 From: tip-bot for Kirill Tkhai Message-ID: Cc: fengguang.wu@intel.com, peterz@infradead.org, mingo@kernel.org, ktkhai@parallels.com, oleg@redhat.com, linux-kernel@vger.kernel.org, hpa@zytor.com, torvalds@linux-foundation.org, tglx@linutronix.de Reply-To: torvalds@linux-foundation.org, hpa@zytor.com, tglx@linutronix.de, oleg@redhat.com, ktkhai@parallels.com, fengguang.wu@intel.com, mingo@kernel.org, peterz@infradead.org, linux-kernel@vger.kernel.org In-Reply-To: <1414473874.8574.2.camel@tkhai> References: <1414473874.8574.2.camel@tkhai> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] sched: Remove lockdep check in sched_move_task () Git-Commit-ID: f7b8a47da17c9ee4998f2ca2018fcc424e953c0e X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: f7b8a47da17c9ee4998f2ca2018fcc424e953c0e Gitweb: http://git.kernel.org/tip/f7b8a47da17c9ee4998f2ca2018fcc424e953c0e Author: Kirill Tkhai AuthorDate: Tue, 28 Oct 2014 08:24:34 +0300 Committer: Ingo Molnar CommitDate: Tue, 4 Nov 2014 07:07:30 +0100 sched: Remove lockdep check in sched_move_task() sched_move_task() is the only interface to change sched_task_group: cpu_cgrp_subsys methods and autogroup_move_group() use it. Everything is synchronized by task_rq_lock(), so cpu_cgroup_attach() is ordered with other users of sched_move_task(). This means we do no need RCU here: if we've dereferenced a tg here, the .attach method hasn't been called for it yet. Thus, we should pass "true" to task_css_check() to silence lockdep warnings. Fixes: eeb61e53ea19 ("sched: Fix race between task_group and sched_task_group") Reported-by: Oleg Nesterov Reported-by: Fengguang Wu Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Link: http://lkml.kernel.org/r/1414473874.8574.2.camel@tkhai Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 240157c..6841fb4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7444,8 +7444,12 @@ void sched_move_task(struct task_struct *tsk) if (unlikely(running)) put_prev_task(rq, tsk); - tg = container_of(task_css_check(tsk, cpu_cgrp_id, - lockdep_is_held(&tsk->sighand->siglock)), + /* + * All callers are synchronized by task_rq_lock(); we do not use RCU + * which is pointless here. Thus, we pass "true" to task_css_check() + * to prevent lockdep warnings. + */ + tg = container_of(task_css_check(tsk, cpu_cgrp_id, true), struct task_group, css); tg = autogroup_task_group(tsk, tg); tsk->sched_task_group = tg;