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 7E606C433F5 for ; Tue, 22 Feb 2022 16:08:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233901AbiBVQIt (ORCPT ); Tue, 22 Feb 2022 11:08:49 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36028 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233602AbiBVQIr (ORCPT ); Tue, 22 Feb 2022 11:08:47 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 6FA9A163D7E for ; Tue, 22 Feb 2022 08:08:21 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1645546100; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type; bh=DwTS4ZAe5En4e5bUnjwAk7/r75DA0tIgyXdfJ7hCMak=; b=etrh3loeYoUQ9o9HDoBhiIc8kDM7yQ0RlJX/wW1EYyEEevffDdZqOmOq0T7hMV3lls0fCe oU9QFy2w8TVj2XTJsekOxmb8HZw5ka6nkFnYeIucL18f7e06d2B8EzKz3JBJV2Q6EX1rv7 wYbBYYy2Tq21HbgPLoB++zMBqRWcFnc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-282-u4u20x2YOeSyFi9jz9Xmhw-1; Tue, 22 Feb 2022 11:08:17 -0500 X-MC-Unique: u4u20x2YOeSyFi9jz9Xmhw-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D4ACF800422; Tue, 22 Feb 2022 16:08:15 +0000 (UTC) Received: from fuller.cnet (ovpn-112-2.gru2.redhat.com [10.97.112.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 422BB8378A; Tue, 22 Feb 2022 16:08:00 +0000 (UTC) Received: by fuller.cnet (Postfix, from userid 1000) id 40D214168B8E; Tue, 22 Feb 2022 13:01:27 -0300 (-03) Date: Tue, 22 Feb 2022 13:01:27 -0300 From: Marcelo Tosatti To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Minchan Kim , Matthew Wilcox , Mel Gorman , Nicolas Saenz Julienne , Juri Lelli , Thomas Gleixner , Sebastian Andrzej Siewior , "Paul E. McKenney" Subject: [patch v2] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On systems that run FIFO:1 applications that busy loop on isolated CPUs, executing tasks on such CPUs under lower priority is undesired (since that will either hang the system, or cause longer interruption to the FIFO task due to execution of lower priority task with very small sched slices). Commit d479960e44f27e0e52ba31b21740b703c538027c ("mm: disable LRU pagevec during the migration temporarily") relies on queueing work items on all online CPUs to ensure visibility of lru_disable_count. However, its possible to use synchronize_rcu which will provide the same guarantees: * synchronize_rcu() waits for preemption disabled * and RCU read side critical sections * For the users of lru_disable_count: * * preempt_disable, local_irq_disable() [bh_lru_lock()] * rcu_read_lock [lru_pvecs CONFIG_PREEMPT_RT] * preempt_disable [lru_pvecs !CONFIG_PREEMPT_RT] * * * so any calls of lru_cache_disabled wrapped by * local_lock+rcu_read_lock or preemption disabled would be * ordered by that. Fixes: [ 1873.243925] INFO: task kworker/u160:0:9 blocked for more than 622 seconds. [ 1873.243927] Tainted: G I --------- --- 5.14.0-31.rt21.31.el9.x86_64 #1 [ 1873.243929] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 1873.243929] task:kworker/u160:0 state:D stack: 0 pid: 9 ppid: 2 flags:0x00004000 [ 1873.243932] Workqueue: cpuset_migrate_mm cpuset_migrate_mm_workfn [ 1873.243936] Call Trace: [ 1873.243938] __schedule+0x21b/0x5b0 [ 1873.243941] schedule+0x43/0xe0 [ 1873.243943] schedule_timeout+0x14d/0x190 [ 1873.243946] ? resched_curr+0x20/0xe0 [ 1873.243953] ? __prepare_to_swait+0x4b/0x70 [ 1873.243958] wait_for_completion+0x84/0xe0 [ 1873.243962] __flush_work.isra.0+0x146/0x200 [ 1873.243966] ? flush_workqueue_prep_pwqs+0x130/0x130 [ 1873.243971] __lru_add_drain_all+0x158/0x1f0 [ 1873.243978] do_migrate_pages+0x3d/0x2d0 [ 1873.243985] ? pick_next_task_fair+0x39/0x3b0 [ 1873.243989] ? put_prev_task_fair+0x1e/0x30 [ 1873.243992] ? pick_next_task+0xb30/0xbd0 [ 1873.243995] ? __tick_nohz_task_switch+0x1e/0x70 [ 1873.244000] ? raw_spin_rq_unlock+0x18/0x60 [ 1873.244002] ? finish_task_switch.isra.0+0xc1/0x2d0 [ 1873.244005] ? __switch_to+0x12f/0x510 [ 1873.244013] cpuset_migrate_mm_workfn+0x22/0x40 [ 1873.244016] process_one_work+0x1e0/0x410 [ 1873.244019] worker_thread+0x50/0x3b0 [ 1873.244022] ? process_one_work+0x410/0x410 [ 1873.244024] kthread+0x173/0x190 [ 1873.244027] ? set_kthread_struct+0x40/0x40 [ 1873.244031] ret_from_fork+0x1f/0x30 Signed-off-by: Marcelo Tosatti v2: rt_spin_lock calls rcu_read_lock, no need to add it before local_lock on swap.c (Nicolas Saenz Julienne) diff --git a/mm/swap.c b/mm/swap.c index bcf3ac288b56..48299a125d68 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -831,8 +831,7 @@ inline void __lru_add_drain_all(bool force_all_cpus) for_each_online_cpu(cpu) { struct work_struct *work = &per_cpu(lru_add_drain_work, cpu); - if (force_all_cpus || - pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) || + if (pagevec_count(&per_cpu(lru_pvecs.lru_add, cpu)) || data_race(pagevec_count(&per_cpu(lru_rotate.pvec, cpu))) || pagevec_count(&per_cpu(lru_pvecs.lru_deactivate_file, cpu)) || pagevec_count(&per_cpu(lru_pvecs.lru_deactivate, cpu)) || @@ -876,14 +875,21 @@ atomic_t lru_disable_count = ATOMIC_INIT(0); void lru_cache_disable(void) { atomic_inc(&lru_disable_count); + synchronize_rcu(); #ifdef CONFIG_SMP /* - * lru_add_drain_all in the force mode will schedule draining on - * all online CPUs so any calls of lru_cache_disabled wrapped by - * local_lock or preemption disabled would be ordered by that. - * The atomic operation doesn't need to have stronger ordering - * requirements because that is enforced by the scheduling - * guarantees. + * synchronize_rcu() waits for preemption disabled + * and RCU read side critical sections. + * For the users of lru_disable_count: + * + * preempt_disable, local_irq_disable [bh_lru_lock()] + * rcu_read_lock [rt_spin_lock CONFIG_PREEMPT_RT] + * preempt_disable [local_lock !CONFIG_PREEMPT_RT] + * + * so any calls of lru_cache_disabled wrapped by local_lock or + * preemption disabled would be ordered by that. The atomic + * operation doesn't need to have stronger ordering requirements + * because that is enforced by the scheduling guarantees. */ __lru_add_drain_all(true); #else