From patchwork Tue Oct 10 20:04:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Peter Zijlstra X-Patchwork-Id: 13415982 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 525BECD8CB7 for ; Tue, 10 Oct 2023 20:05:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=XE2HwTU4b17DFNAvyMLs00xUHflfotyCEK2qjvZ4nlM=; b=FUNCV8mLBfMgLA +XQE2bteoIsLdRyFxK9GWoOeS1gx6iEGb5JgU5d/ksT1l/av7M653rClgoVkAujm5YhM3PwUkLE8k v2PClLp2DYf48Anqf9hu8ayGyOFSZUd9RDfJapjmVKeKSJRKKSpeUSVnH349DcEJ1ITmdwG55vMZE pKxVXIvo4UWIRQaXD2FE7cU0p+SWVP+jMSWIuEHU7ZtomeUvQ7xOnSN1ZR1NPimq1vLRLJbhZYoc4 K2D8NLUS7n1WfVlYQ3jxh5tD4xfF+MUOppwaKv6BWCnuVO29okvjeFi+lXhHuzYPAEVSHX+xq7yLI pxj15XjpEQDY4OMZM0Pw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qqIyI-00E5qB-0z; Tue, 10 Oct 2023 20:04:50 +0000 Received: from casper.infradead.org ([2001:8b0:10b:1236::1]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1qqIyH-00E5pv-2S; Tue, 10 Oct 2023 20:04:49 +0000 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=3oQwwKYwoiZ0SHY/ewVGJIxzoCy1EpL15euKfoG+Nm4=; b=nxi6ki9eV37suWsQbArzTWN5mq glkierP26zkTuu3TneEwh+vLLif+J+JUOQjIwvfjvmbZ2t3lHsUI1QvpsZ/Q8Wc9DffoUYmTO0CFl 7jV6RY8nuwENh5D7inZnNa1rROwNs9rImi4QgioqXpF4EzzKbR1nd5gzfrFomqA6A7yZSgCcDwOhc H3ETW0vty5I53RP0RYb36cggPiwx33fDh8P47Tzu0cIYvd0CStWflEDH+RlYO0arSoQ5fSea1uPDj mXHSeNHcByNcXmMM8PItN11/P4DDcFXfD0do1T9oENp1qh44BVxUT2X+fJpIMBLcYrcADqFBhbZJE DhdWwCpw==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1qqIyA-006Y9B-U1; Tue, 10 Oct 2023 20:04:43 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 3A292300392; Tue, 10 Oct 2023 22:04:42 +0200 (CEST) Date: Tue, 10 Oct 2023 22:04:42 +0200 From: Peter Zijlstra To: Kuyo Chang =?utf-8?b?KOW8teW7uuaWhyk=?= Cc: "dietmar.eggemann@arm.com" , "linux-kernel@vger.kernel.org" , "linux-mediatek@lists.infradead.org" , "rostedt@goodmis.org" , wsd_upstream , "vschneid@redhat.com" , "bristot@redhat.com" , "juri.lelli@redhat.com" , "mingo@redhat.com" , "linux-arm-kernel@lists.infradead.org" , "bsegall@google.com" , "mgorman@suse.de" , "matthias.bgg@gmail.com" , "vincent.guittot@linaro.org" , "angelogioacchino.delregno@collabora.com" Subject: [PATCH] sched: Fix stop_one_cpu_nowait() vs hotplug Message-ID: <20231010200442.GA16515@noisy.programming.kicks-ass.net> References: <20230927033431.12406-1-kuyo.chang@mediatek.com> <20230927080850.GB21824@noisy.programming.kicks-ass.net> <20230929102135.GD6282@noisy.programming.kicks-ass.net> <8ad1b617a1040ce4cc56a5d04e8219b5313a9a6e.camel@mediatek.com> <20231010145747.GQ377@noisy.programming.kicks-ass.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20231010145747.GQ377@noisy.programming.kicks-ass.net> X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Oct 10, 2023 at 04:57:47PM +0200, Peter Zijlstra wrote: > On Tue, Oct 10, 2023 at 02:40:22PM +0000, Kuyo Chang (張建文) wrote: > > It is running good so far(more than a week)on hotplug/set affinity > > stress test. I will keep it testing and report back if it happens > > again. > > OK, I suppose I should look at writing a coherent Changelog for this > then... Something like the below... ? --- Subject: sched: Fix stop_one_cpu_nowait() vs hotplug From: Peter Zijlstra Date: Tue Oct 10 20:57:39 CEST 2023 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)" --- kernel/sched/core.c | 10 ++++++++-- kernel/sched/deadline.c | 2 ++ kernel/sched/fair.c | 4 +++- 3 files changed, 13 insertions(+), 3 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2645,9 +2645,11 @@ 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: @@ -2967,12 +2969,13 @@ static int affine_move_task(struct rq *r 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); @@ -3038,12 +3041,13 @@ static int affine_move_task(struct rq *r 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; @@ -9459,9 +9463,11 @@ 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 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2420,9 +2420,11 @@ static void pull_dl_task(struct rq *this 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); } } --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -11299,13 +11299,15 @@ static int load_balance(int this_cpu, st 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;