Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933904AbaJ1FYm (ORCPT ); Tue, 28 Oct 2014 01:24:42 -0400 Received: from relay.parallels.com ([195.214.232.42]:47912 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933696AbaJ1FYk (ORCPT ); Tue, 28 Oct 2014 01:24:40 -0400 Message-ID: <1414473874.8574.2.camel@tkhai> Subject: Re: [PATCH] sched: Fix race between task_group and sched_task_group From: Kirill Tkhai To: Oleg Nesterov CC: , Peter Zijlstra , Ingo Molnar , Burke Libbey , Vladimir Davydov , Kirill Tkhai Date: Tue, 28 Oct 2014 08:24:34 +0300 In-Reply-To: <20141027230427.GA18454@redhat.com> References: <1414405105.19914.169.camel@tkhai> <20141027230427.GA18454@redhat.com> Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5-2+b3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org В Вт, 28/10/2014 в 00:04 +0100, Oleg Nesterov пишет: > On 10/27, Kirill Tkhai wrote: > > > > +static void cpu_cgroup_fork(struct task_struct *task) > > +{ > > + sched_move_task(task); > > +} > > + > > static int cpu_cgroup_can_attach(struct cgroup_subsys_state *css, > > struct cgroup_taskset *tset) > > { > > @@ -8205,6 +8210,7 @@ struct cgroup_subsys cpu_cgrp_subsys = { > > .css_free = cpu_cgroup_css_free, > > .css_online = cpu_cgroup_css_online, > > .css_offline = cpu_cgroup_css_offline, > > + .fork = cpu_cgroup_fork, > > Agreed, but it seems that sched_move_task() -> task_css_check() can > complain if CONFIG_PROVE_RCU... Thanks, Oleg. > > cpu_cgroup_exit() too calls sched_move_task() without any lock, but > there is the PF_EXITING check and init_css_set can't go away. > > perhaps sched_move_task() should just take rcu_read_lock() and use > task_css() ? This lockdep_is_held(siglock) looks ugly, and iiuc we > need it to shut up the warning if autogroup_move_group() is the caller. Shouldn't we do that in separate patch? How about this? [PATCH]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. Signed-off-by: Kirill Tkhai Reported-by: Oleg Nesterov diff --git a/kernel/sched/core.c b/kernel/sched/core.c index dde8adb..d77e6ee 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7403,8 +7403,12 @@ 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; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/