From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753499AbbJTJeA (ORCPT ); Tue, 20 Oct 2015 05:34:00 -0400 Received: from terminus.zytor.com ([198.137.202.10]:49749 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751036AbbJTJd5 (ORCPT ); Tue, 20 Oct 2015 05:33:57 -0400 Date: Tue, 20 Oct 2015 02:33:20 -0700 From: tip-bot for Oleg Nesterov Message-ID: Cc: peterz@infradead.org, tglx@linutronix.de, mingo@kernel.org, oleg@redhat.com, riel@redhat.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, tj@kernel.org, hpa@zytor.com, efault@gmx.de, paulmck@linux.vnet.ibm.com, torvalds@linux-foundation.org Reply-To: riel@redhat.com, mingo@kernel.org, oleg@redhat.com, peterz@infradead.org, tglx@linutronix.de, torvalds@linux-foundation.org, paulmck@linux.vnet.ibm.com, efault@gmx.de, hpa@zytor.com, tj@kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org In-Reply-To: <20151008170141.GA25537@redhat.com> References: <20151008170141.GA25537@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] stop_machine: Change cpu_stop_queue_two_works() to rely on stopper->enabled Git-Commit-ID: d8bc853582bfd81a9c08ca6922aeb01570080ccc 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: d8bc853582bfd81a9c08ca6922aeb01570080ccc Gitweb: http://git.kernel.org/tip/d8bc853582bfd81a9c08ca6922aeb01570080ccc Author: Oleg Nesterov AuthorDate: Thu, 8 Oct 2015 19:01:41 +0200 Committer: Ingo Molnar CommitDate: Tue, 20 Oct 2015 10:23:55 +0200 stop_machine: Change cpu_stop_queue_two_works() to rely on stopper->enabled Change cpu_stop_queue_two_works() to ensure that both CPU's have stopper->enabled == T or fail otherwise. This way stop_two_cpus() no longer needs to check cpu_active() to avoid the deadlock. This patch doesn't remove these checks, we will do this later. Note: we need to take both stopper->lock's at the same time, but this will also help to remove lglock from stop_machine.c, so I hope this is fine. Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Mike Galbraith Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Rik van Riel Cc: Tejun Heo Cc: Thomas Gleixner Cc: heiko.carstens@de.ibm.com Link: http://lkml.kernel.org/r/20151008170141.GA25537@redhat.com Signed-off-by: Ingo Molnar --- kernel/stop_machine.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-) diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c index 688d6b3..91fbb10 100644 --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -219,12 +219,27 @@ static int multi_cpu_stop(void *data) static int cpu_stop_queue_two_works(int cpu1, struct cpu_stop_work *work1, int cpu2, struct cpu_stop_work *work2) { + struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1); + struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2); + int err; + lg_double_lock(&stop_cpus_lock, cpu1, cpu2); - cpu_stop_queue_work(cpu1, work1); - cpu_stop_queue_work(cpu2, work2); + spin_lock_irq(&stopper1->lock); + spin_lock_nested(&stopper2->lock, SINGLE_DEPTH_NESTING); + + err = -ENOENT; + if (!stopper1->enabled || !stopper2->enabled) + goto unlock; + + err = 0; + __cpu_stop_queue_work(stopper1, work1); + __cpu_stop_queue_work(stopper2, work2); +unlock: + spin_unlock(&stopper2->lock); + spin_unlock_irq(&stopper1->lock); lg_double_unlock(&stop_cpus_lock, cpu1, cpu2); - return 0; + return err; } /** * stop_two_cpus - stops two cpus @@ -261,12 +276,8 @@ int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void * set_state(&msdata, MULTI_STOP_PREPARE); /* - * If we observe both CPUs active we know _cpu_down() cannot yet have - * queued its stop_machine works and therefore ours will get executed - * first. Or its not either one of our CPUs that's getting unplugged, - * in which case we don't care. - * - * This relies on the stopper workqueues to be FIFO. + * We do not want to migrate to inactive CPU. FIXME: move this + * into migrate_swap_stop() callback. */ if (!cpu_active(cpu1) || !cpu_active(cpu2)) { preempt_enable();