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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D22F8C2BB3F for ; Wed, 15 Nov 2023 19:52:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235503AbjKOTw4 (ORCPT ); Wed, 15 Nov 2023 14:52:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235498AbjKOTwz (ORCPT ); Wed, 15 Nov 2023 14:52:55 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5745812C for ; Wed, 15 Nov 2023 11:52:52 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CF89AC433C8; Wed, 15 Nov 2023 19:52:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1700077972; bh=kRiwSO2or1SHqhDQgcuIZG8K7RLtSHpmK9ULnCs3jnc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M7TbzD5aUxUuzWfAEmyTZDe44aS+V/Kg6O9VqlYY99O+0Oi0QFYRLg47KEZAU/0LM Ay0w1iibqCPROb2oNFJhqtzuB51pYAIHOmOSU/C/zVXiLs0atDgZTTS6ZCMWzEBBz6 CgRm46W6LfYOeE6RS4G0S4pZJByu8Q0LZCQtf1mk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Kuyo=20Chang=20 ?= , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 6.1 007/379] sched: Fix stop_one_cpu_nowait() vs hotplug Date: Wed, 15 Nov 2023 14:21:22 -0500 Message-ID: <20231115192645.576433491@linuxfoundation.org> X-Mailer: git-send-email 2.42.1 In-Reply-To: <20231115192645.143643130@linuxfoundation.org> References: <20231115192645.143643130@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra [ Upstream commit f0498d2a54e7966ce23cd7c7ff42c64fa0059b07 ] Kuyo reported sporadic failures on a sched_setaffinity() vs CPU hotplug stress-test -- notably affine_move_task() remains stuck in wait_for_completion(), leading to a hung-task detector warning. Specifically, it was reported that stop_one_cpu_nowait(.fn = migration_cpu_stop) returns false -- this stopper is responsible for the matching complete(). The race scenario is: CPU0 CPU1 // doing _cpu_down() __set_cpus_allowed_ptr() task_rq_lock(); takedown_cpu() stop_machine_cpuslocked(take_cpu_down..) ack_state() MULTI_STOP_RUN take_cpu_down() __cpu_disable(); stop_machine_park(); stopper->enabled = false; /> /> stop_one_cpu_nowait(.fn = migration_cpu_stop); if (stopper->enabled) // false!!! That is, by doing stop_one_cpu_nowait() after dropping rq-lock, the stopper thread gets a chance to preempt and allows the cpu-down for the target CPU to complete. OTOH, since stop_one_cpu_nowait() / cpu_stop_queue_work() needs to issue a wakeup, it must not be ran under the scheduler locks. Solve this apparent contradiction by keeping preemption disabled over the unlock + queue_stopper combination: preempt_disable(); task_rq_unlock(...); if (!stop_pending) stop_one_cpu_nowait(...) preempt_enable(); This respects the lock ordering contraints while still avoiding the above race. That is, if we find the CPU is online under rq-lock, the targeted stop_one_cpu_nowait() must succeed. Apply this pattern to all similar stop_one_cpu_nowait() invocations. Fixes: 6d337eab041d ("sched: Fix migrate_disable() vs set_cpus_allowed_ptr()") Reported-by: "Kuyo Chang (張建文)" Signed-off-by: Peter Zijlstra (Intel) Tested-by: "Kuyo Chang (張建文)" Link: https://lkml.kernel.org/r/20231010200442.GA16515@noisy.programming.kicks-ass.net Signed-off-by: Sasha Levin --- kernel/sched/core.c | 10 ++++++++-- kernel/sched/deadline.c | 2 ++ kernel/sched/fair.c | 4 +++- kernel/sched/rt.c | 4 ++++ 4 files changed, 17 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 55d13980e29fd..18a4f8f28a25f 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2463,9 +2463,11 @@ static int migration_cpu_stop(void *data) * it. */ WARN_ON_ONCE(!pending->stop_pending); + preempt_disable(); task_rq_unlock(rq, p, &rf); stop_one_cpu_nowait(task_cpu(p), migration_cpu_stop, &pending->arg, &pending->stop_work); + preempt_enable(); return 0; } out: @@ -2746,12 +2748,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag complete = true; } + preempt_disable(); task_rq_unlock(rq, p, rf); - if (push_task) { stop_one_cpu_nowait(rq->cpu, push_cpu_stop, p, &rq->push_work); } + preempt_enable(); if (complete) complete_all(&pending->done); @@ -2817,12 +2820,13 @@ static int affine_move_task(struct rq *rq, struct task_struct *p, struct rq_flag if (flags & SCA_MIGRATE_ENABLE) p->migration_flags &= ~MDF_PUSH; + preempt_disable(); task_rq_unlock(rq, p, rf); - if (!stop_pending) { stop_one_cpu_nowait(cpu_of(rq), migration_cpu_stop, &pending->arg, &pending->stop_work); } + preempt_enable(); if (flags & SCA_MIGRATE_ENABLE) return 0; @@ -9255,9 +9259,11 @@ static void balance_push(struct rq *rq) * Temporarily drop rq->lock such that we can wake-up the stop task. * Both preemption and IRQs are still disabled. */ + preempt_disable(); raw_spin_rq_unlock(rq); stop_one_cpu_nowait(rq->cpu, __balance_push_cpu_stop, push_task, this_cpu_ptr(&push_work)); + preempt_enable(); /* * At this point need_resched() is true and we'll take the loop in * schedule(). The next pick is obviously going to be the stop task diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 9ce9810861ba5..389290e950bea 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2460,9 +2460,11 @@ static void pull_dl_task(struct rq *this_rq) double_unlock_balance(this_rq, src_rq); if (push_task) { + preempt_disable(); raw_spin_rq_unlock(this_rq); stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop, push_task, &src_rq->push_work); + preempt_enable(); raw_spin_rq_lock(this_rq); } } diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e7ae0ba3fd0bc..2558ab9033bee 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10713,13 +10713,15 @@ static int load_balance(int this_cpu, struct rq *this_rq, busiest->push_cpu = this_cpu; active_balance = 1; } - raw_spin_rq_unlock_irqrestore(busiest, flags); + preempt_disable(); + raw_spin_rq_unlock_irqrestore(busiest, flags); if (active_balance) { stop_one_cpu_nowait(cpu_of(busiest), active_load_balance_cpu_stop, busiest, &busiest->active_balance_work); } + preempt_enable(); } } else { sd->nr_balance_failed = 0; diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 576eb2f51f043..76bafa8d331a7 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2109,9 +2109,11 @@ static int push_rt_task(struct rq *rq, bool pull) */ push_task = get_push_task(rq); if (push_task) { + preempt_disable(); raw_spin_rq_unlock(rq); stop_one_cpu_nowait(rq->cpu, push_cpu_stop, push_task, &rq->push_work); + preempt_enable(); raw_spin_rq_lock(rq); } @@ -2448,9 +2450,11 @@ static void pull_rt_task(struct rq *this_rq) double_unlock_balance(this_rq, src_rq); if (push_task) { + preempt_disable(); raw_spin_rq_unlock(this_rq); stop_one_cpu_nowait(src_rq->cpu, push_cpu_stop, push_task, &src_rq->push_work); + preempt_enable(); raw_spin_rq_lock(this_rq); } } -- 2.42.0