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 2EB10C433EF for ; Fri, 14 Jan 2022 08:18:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237177AbiANISx (ORCPT ); Fri, 14 Jan 2022 03:18:53 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:57808 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239773AbiANISZ (ORCPT ); Fri, 14 Jan 2022 03:18:25 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id EACD661E06; Fri, 14 Jan 2022 08:18:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7101AC36AEA; Fri, 14 Jan 2022 08:18:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1642148304; bh=bwY1J0+2FxiQIAXC8w5Wtk4azTdHcn+x77aWhc5xcfM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FGM76jFQG93RgDyy8NWGJ3aSsxNyoK0f39wZ8JZmEOrOIpCSSH85ocFR4eYVc9XtL HVo3sAvC1ju8XE8Cc1j/PoBni7yalqR8EJdw8hbU0aWzPDVXdlc9b2ncYA9FFS9dIb Que3CeE5fQb4yV4pNoK4R4J+XJrxyG/1EMUi8EtY= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Lai Jiangshan , "Paul E. McKenney" , "Peter Zijlstra (Intel)" , Frederic Weisbecker , Thomas Gleixner , Ingo Molnar , Sebastian Andrzej Siewior , Daniel Bristot de Oliveira , Tejun Heo Subject: [PATCH 5.10 02/25] workqueue: Fix unbind_workers() VS wq_worker_running() race Date: Fri, 14 Jan 2022 09:16:10 +0100 Message-Id: <20220114081542.775427055@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220114081542.698002137@linuxfoundation.org> References: <20220114081542.698002137@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Frederic Weisbecker commit 07edfece8bcb0580a1828d939e6f8d91a8603eb2 upstream. At CPU-hotplug time, unbind_worker() may preempt a worker while it is waking up. In that case the following scenario can happen: unbind_workers() wq_worker_running() -------------- ------------------- if (!(worker->flags & WORKER_NOT_RUNNING)) //PREEMPTED by unbind_workers worker->flags |= WORKER_UNBOUND; [...] atomic_set(&pool->nr_running, 0); //resume to worker atomic_inc(&worker->pool->nr_running); After unbind_worker() resets pool->nr_running, the value is expected to remain 0 until the pool ever gets rebound in case cpu_up() is called on the target CPU in the future. But here the race leaves pool->nr_running with a value of 1, triggering the following warning when the worker goes idle: WARNING: CPU: 3 PID: 34 at kernel/workqueue.c:1823 worker_enter_idle+0x95/0xc0 Modules linked in: CPU: 3 PID: 34 Comm: kworker/3:0 Not tainted 5.16.0-rc1+ #34 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014 Workqueue: 0x0 (rcu_par_gp) RIP: 0010:worker_enter_idle+0x95/0xc0 Code: 04 85 f8 ff ff ff 39 c1 7f 09 48 8b 43 50 48 85 c0 74 1b 83 e2 04 75 99 8b 43 34 39 43 30 75 91 8b 83 00 03 00 00 85 c0 74 87 <0f> 0b 5b c3 48 8b 35 70 f1 37 01 48 8d 7b 48 48 81 c6 e0 93 0 RSP: 0000:ffff9b7680277ed0 EFLAGS: 00010086 RAX: 00000000ffffffff RBX: ffff93465eae9c00 RCX: 0000000000000000 RDX: 0000000000000000 RSI: ffff9346418a0000 RDI: ffff934641057140 RBP: ffff934641057170 R08: 0000000000000001 R09: ffff9346418a0080 R10: ffff9b768027fdf0 R11: 0000000000002400 R12: ffff93465eae9c20 R13: ffff93465eae9c20 R14: ffff93465eae9c70 R15: ffff934641057140 FS: 0000000000000000(0000) GS:ffff93465eac0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000000 CR3: 000000001cc0c000 CR4: 00000000000006e0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: worker_thread+0x89/0x3d0 ? process_one_work+0x400/0x400 kthread+0x162/0x190 ? set_kthread_struct+0x40/0x40 ret_from_fork+0x22/0x30 Also due to this incorrect "nr_running == 1", further queued work may end up not being served, because no worker is awaken at work insert time. This raises rcutorture writer stalls for example. Fix this with disabling preemption in the right place in wq_worker_running(). It's worth noting that if the worker migrates and runs concurrently with unbind_workers(), it is guaranteed to see the WORKER_UNBOUND flag update due to set_cpus_allowed_ptr() acquiring/releasing rq->lock. Fixes: 6d25be5782e4 ("sched/core, workqueues: Distangle worker accounting from rq lock") Reviewed-by: Lai Jiangshan Tested-by: Paul E. McKenney Acked-by: Peter Zijlstra (Intel) Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Sebastian Andrzej Siewior Cc: Daniel Bristot de Oliveira Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- kernel/workqueue.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -850,8 +850,17 @@ void wq_worker_running(struct task_struc if (!worker->sleeping) return; + + /* + * If preempted by unbind_workers() between the WORKER_NOT_RUNNING check + * and the nr_running increment below, we may ruin the nr_running reset + * and leave with an unexpected pool->nr_running == 1 on the newly unbound + * pool. Protect against such race. + */ + preempt_disable(); if (!(worker->flags & WORKER_NOT_RUNNING)) atomic_inc(&worker->pool->nr_running); + preempt_enable(); worker->sleeping = 0; }