From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:55570 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965515AbeFRIWf (ORCPT ); Mon, 18 Jun 2018 04:22:35 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Peter Zijlstra (Intel)" , Matt Fleming , Linus Torvalds , Michal Hocko , Mike Galbraith , Thomas Gleixner , Ingo Molnar , Sasha Levin Subject: [PATCH 4.16 159/279] stop_machine, sched: Fix migrate_swap() vs. active_balance() deadlock Date: Mon, 18 Jun 2018 10:12:24 +0200 Message-Id: <20180618080615.404029993@linuxfoundation.org> In-Reply-To: <20180618080608.851973560@linuxfoundation.org> References: <20180618080608.851973560@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra [ Upstream commit 0b26351b910fb8fe6a056f8a1bbccabe50c0e19f ] Matt reported the following deadlock: CPU0 CPU1 schedule(.prev=migrate/0) pick_next_task() ... idle_balance() migrate_swap() active_balance() stop_two_cpus() spin_lock(stopper0->lock) spin_lock(stopper1->lock) ttwu(migrate/0) smp_cond_load_acquire() -- waits for schedule() stop_one_cpu(1) spin_lock(stopper1->lock) -- waits for stopper lock Fix this deadlock by taking the wakeups out from under stopper->lock. This allows the active_balance() to queue the stop work and finish the context switch, which in turn allows the wakeup from migrate_swap() to observe the context and complete the wakeup. Signed-off-by: Peter Zijlstra (Intel) Reported-by: Matt Fleming Signed-off-by: Peter Zijlstra (Intel) Acked-by: Matt Fleming Cc: Linus Torvalds Cc: Michal Hocko Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20180420095005.GH4064@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/stop_machine.c | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) --- a/kernel/stop_machine.c +++ b/kernel/stop_machine.c @@ -21,6 +21,7 @@ #include #include #include +#include /* * Structure to determine completion condition and record errors. May @@ -65,27 +66,31 @@ static void cpu_stop_signal_done(struct } static void __cpu_stop_queue_work(struct cpu_stopper *stopper, - struct cpu_stop_work *work) + struct cpu_stop_work *work, + struct wake_q_head *wakeq) { list_add_tail(&work->list, &stopper->works); - wake_up_process(stopper->thread); + wake_q_add(wakeq, stopper->thread); } /* queue @work to @stopper. if offline, @work is completed immediately */ static bool cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work) { struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu); + DEFINE_WAKE_Q(wakeq); unsigned long flags; bool enabled; spin_lock_irqsave(&stopper->lock, flags); enabled = stopper->enabled; if (enabled) - __cpu_stop_queue_work(stopper, work); + __cpu_stop_queue_work(stopper, work, &wakeq); else if (work->done) cpu_stop_signal_done(work->done); spin_unlock_irqrestore(&stopper->lock, flags); + wake_up_q(&wakeq); + return enabled; } @@ -229,6 +234,7 @@ static int cpu_stop_queue_two_works(int { struct cpu_stopper *stopper1 = per_cpu_ptr(&cpu_stopper, cpu1); struct cpu_stopper *stopper2 = per_cpu_ptr(&cpu_stopper, cpu2); + DEFINE_WAKE_Q(wakeq); int err; retry: spin_lock_irq(&stopper1->lock); @@ -252,8 +258,8 @@ retry: goto unlock; err = 0; - __cpu_stop_queue_work(stopper1, work1); - __cpu_stop_queue_work(stopper2, work2); + __cpu_stop_queue_work(stopper1, work1, &wakeq); + __cpu_stop_queue_work(stopper2, work2, &wakeq); unlock: spin_unlock(&stopper2->lock); spin_unlock_irq(&stopper1->lock); @@ -263,6 +269,9 @@ unlock: cpu_relax(); goto retry; } + + wake_up_q(&wakeq); + return err; } /**