From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752515AbaI0IlJ (ORCPT ); Sat, 27 Sep 2014 04:41:09 -0400 Received: from forward1l.mail.yandex.net ([84.201.143.144]:58467 "EHLO forward1l.mail.yandex.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751885AbaI0IlD (ORCPT ); Sat, 27 Sep 2014 04:41:03 -0400 X-Yandex-Uniq: 9c25fd92-2837-4a2e-b9ab-ba2f183b845d Authentication-Results: smtp3o.mail.yandex.net; dkim=pass header.i=@yandex.ru Subject: [PATCH 1/2] sched/dl: Implement cancel_dl_timer() to use in switched_from_dl() From: Kirill Tkhai To: linux-kernel@vger.kernel.org Cc: Peter Zijlstra , Kirill Tkhai , Ingo Molnar , Juri Lelli Date: Sat, 27 Sep 2014 12:40:58 +0400 Message-ID: <20140927084044.1634.60573.stgit@localhost> User-Agent: StGit/0.17.1-dirty MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kirill Tkhai hrtimer_try_to_cancel() may bring a suprise, and even two its calls may fail. So, let's implement 100% guaranteed way to cancel the timer and let's be sure we are safe even in very unlikely situations. We do not create any problem with rq unlocking, because it already may happed below in pull_dl_task(). No problem with deadline tasks balancing too. Signed-off-by: Kirill Tkhai --- kernel/sched/deadline.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index abfaf3d..63f8b4a 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -555,11 +555,6 @@ void init_dl_task_timer(struct sched_dl_entity *dl_se) { struct hrtimer *timer = &dl_se->dl_timer; - if (hrtimer_active(timer)) { - hrtimer_try_to_cancel(timer); - return; - } - hrtimer_init(timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); timer->function = dl_task_timer; } @@ -1567,10 +1562,34 @@ void init_sched_dl_class(void) #endif /* CONFIG_SMP */ +/* + * Surely cancel task's dl_timer. May drop rq->lock. + */ +static void cancel_dl_timer(struct rq *rq, struct task_struct *p) +{ + struct hrtimer *dl_timer = &p->dl.dl_timer; + + /* Nobody will change task's class if pi_lock is held */ + lockdep_assert_held(&p->pi_lock); + + if (hrtimer_active(dl_timer)) { + int ret = hrtimer_try_to_cancel(dl_timer); + + if (unlikely(ret == -1)) { + /* + * Note, p may migrate OR new deadline tasks + * may appear in rq when we are unlocking it. + */ + raw_spin_unlock(&rq->lock); + hrtimer_cancel(dl_timer); + raw_spin_lock(&rq->lock); + } + } +} + static void switched_from_dl(struct rq *rq, struct task_struct *p) { - if (hrtimer_active(&p->dl.dl_timer) && !dl_policy(p->policy)) - hrtimer_try_to_cancel(&p->dl.dl_timer); + cancel_dl_timer(rq, p); __dl_clear_params(p);