From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E793C43142 for ; Thu, 2 Aug 2018 12:07:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0CA2C214F1 for ; Thu, 2 Aug 2018 12:07:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0CA2C214F1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=zytor.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732372AbeHBN6O (ORCPT ); Thu, 2 Aug 2018 09:58:14 -0400 Received: from terminus.zytor.com ([198.137.202.136]:48141 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732034AbeHBN6O (ORCPT ); Thu, 2 Aug 2018 09:58:14 -0400 Received: from terminus.zytor.com (localhost [127.0.0.1]) by terminus.zytor.com (8.15.2/8.15.2) with ESMTPS id w72C6tAS3494026 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Thu, 2 Aug 2018 05:06:55 -0700 Received: (from tipbot@localhost) by terminus.zytor.com (8.15.2/8.15.2/Submit) id w72C6tNR3494023; Thu, 2 Aug 2018 05:06:55 -0700 Date: Thu, 2 Aug 2018 05:06:55 -0700 X-Authentication-Warning: terminus.zytor.com: tipbot set sender to tipbot@zytor.com using -f From: tip-bot for Peter Zijlstra Message-ID: Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, peterz@infradead.org, bigeasy@linutronix.de, mingo@kernel.org, hpa@zytor.com Reply-To: mingo@kernel.org, hpa@zytor.com, bigeasy@linutronix.de, peterz@infradead.org, tglx@linutronix.de, linux-kernel@vger.kernel.org In-Reply-To: <20180730112140.GH2494@hirez.programming.kicks-ass.net> References: <20180730112140.GH2494@hirez.programming.kicks-ass.net> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] stop_machine: Reflow cpu_stop_queue_two_works() Git-Commit-ID: 2171ce2d470d6e389ebbef3edd22c7643918a02f 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 2171ce2d470d6e389ebbef3edd22c7643918a02f Gitweb: https://git.kernel.org/tip/2171ce2d470d6e389ebbef3edd22c7643918a02f Author: Peter Zijlstra AuthorDate: Mon, 30 Jul 2018 13:21:40 +0200 Committer: Thomas Gleixner CommitDate: Thu, 2 Aug 2018 14:02:53 +0200 stop_machine: Reflow cpu_stop_queue_two_works() The code flow in cpu_stop_queue_two_works() is a little arcane; fix this by lifting the preempt_disable() to the top to create more natural nesting wrt the spinlocks and make the wake_up_q() and preempt_enable() unconditional at the end. Furthermore, enable preemption in the -EDEADLK case, such that we spin-wait with preemption enabled. Suggested-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Cc: Sebastian Andrzej Siewior Cc: isaacm@codeaurora.org Cc: matt@codeblueprint.co.uk Cc: psodagud@codeaurora.org Cc: gregkh@linuxfoundation.org Cc: pkondeti@codeaurora.org Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20180730112140.GH2494@hirez.programming.kicks-ass.net --- kernel/stop_machine.c | 41 +++++++++++++++++++++++------------------ 1 file changed, 23 insertions(+), 18 deletions(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index e190d1ef3a23..34b6652e8677 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -236,13 +236,24 @@ static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1, struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2); DEFINE_WAKE_Q(wakeq); int err; + retry: + /* + * The waking up of stopper threads has to happen in the same + * scheduling context as the queueing. Otherwise, there is a + * possibility of one of the above stoppers being woken up by another + * CPU, and preempting us. This will cause us to not wake up the other + * stopper forever. + */ + preempt_disable(); raw_spin_lock_irq(&stopper1->lock); raw_spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING); - err = -ENOENT; - if (!stopper1->enabled || !stopper2->enabled) + if (!stopper1->enabled || !stopper2->enabled) { + err = -ENOENT; goto unlock; + } + /* * Ensure that if we race with __stop_cpus() the stoppers won't get * queued up in reverse order leading to system deadlock. @@ -253,36 +264,30 @@ retry: * It can be falsely true but it is safe to spin until it is cleared, * queue_stop_cpus_work() does everything under preempt_disable(). */ - err = -EDEADLK; - if (unlikely(stop_cpus_in_progress)) - goto unlock; + if (unlikely(stop_cpus_in_progress)) { + err = -EDEADLK; + goto unlock; + } err = 0; __cpu_stop_queue_work(stopper1, work1, &wakeq); __cpu_stop_queue_work(stopper2, work2, &wakeq); - /* - * The waking up of stopper threads has to happen - * in the same scheduling context as the queueing. - * Otherwise, there is a possibility of one of the - * above stoppers being woken up by another CPU, - * and preempting us. This will cause us to n ot - * wake up the other stopper forever. - */ - preempt_disable(); + unlock: raw_spin_unlock(&stopper2->lock); raw_spin_unlock_irq(&stopper1->lock); if (unlikely(err == -EDEADLK)) { + preempt_enable(); + while (stop_cpus_in_progress) cpu_relax(); + goto retry; } - if (!err) { - wake_up_q(&wakeq); - preempt_enable(); - } + wake_up_q(&wakeq); + preempt_enable(); return err; }