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 30532C433EF for ; Tue, 19 Apr 2022 00:00:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236116AbiDSADH (ORCPT ); Mon, 18 Apr 2022 20:03:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236108AbiDSAC6 (ORCPT ); Mon, 18 Apr 2022 20:02:58 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C80211C34; Mon, 18 Apr 2022 17:00:17 -0700 (PDT) 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 CF3BE6128A; Tue, 19 Apr 2022 00:00:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 30AA4C385A8; Tue, 19 Apr 2022 00:00:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1650326416; bh=B3FKOAVi0h12Jmquk99abkkXI6DRfWVVNn7fsz2s47Y=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=eIyVIelsePL2hXcgK1LeA+D2oq1psbS3en+cIiWfV7CXR5CSKfcL1p4YR/RyUp8ia S8NKPlNqDslxqSV7Ze5lTntCIkums0iS3VJCgwe+BKyEEs9wD2xtXD7NusbV5suYKl LBRPZga+AsvMFW+fabpwlOd+621ojGTW/xp9GgJiNRbKb6hdsZv6i/YySjaJ3pg2LQ NDX6paN4TEYkdD8Q/VtTaTDYFcZYGHMJ3vhtzVDgqrmnrclZ15bSwyYHzCsD8lRXvo PXgW1s9rH/OZomfLNHgOg9o4UNnJ0PPM4NPY5u2H3MjsbqJiPdbvJvaCfwL5ysvr5e v4KpUy+s8l4lQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id D5D605C04BD; Mon, 18 Apr 2022 17:00:15 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Padmanabha Srinivasaiah , "Paul E . McKenney" Subject: [PATCH rcu 1/9] rcu-tasks: Fix race in schedule and flush work Date: Mon, 18 Apr 2022 17:00:06 -0700 Message-Id: <20220419000014.3948512-1-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220419000007.GA3945818@paulmck-ThinkPad-P17-Gen-1> References: <20220419000007.GA3945818@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Padmanabha Srinivasaiah While booting secondary CPUs, cpus_read_[lock/unlock] is not keeping online cpumask stable. The transient online mask results in below calltrace. [ 0.324121] CPU1: Booted secondary processor 0x0000000001 [0x410fd083] [ 0.346652] Detected PIPT I-cache on CPU2 [ 0.347212] CPU2: Booted secondary processor 0x0000000002 [0x410fd083] [ 0.377255] Detected PIPT I-cache on CPU3 [ 0.377823] CPU3: Booted secondary processor 0x0000000003 [0x410fd083] [ 0.379040] ------------[ cut here ]------------ [ 0.383662] WARNING: CPU: 0 PID: 10 at kernel/workqueue.c:3084 __flush_work+0x12c/0x138 [ 0.384850] Modules linked in: [ 0.385403] CPU: 0 PID: 10 Comm: rcu_tasks_rude_ Not tainted 5.17.0-rc3-v8+ #13 [ 0.386473] Hardware name: Raspberry Pi 4 Model B Rev 1.4 (DT) [ 0.387289] pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 0.388308] pc : __flush_work+0x12c/0x138 [ 0.388970] lr : __flush_work+0x80/0x138 [ 0.389620] sp : ffffffc00aaf3c60 [ 0.390139] x29: ffffffc00aaf3d20 x28: ffffffc009c16af0 x27: ffffff80f761df48 [ 0.391316] x26: 0000000000000004 x25: 0000000000000003 x24: 0000000000000100 [ 0.392493] x23: ffffffffffffffff x22: ffffffc009c16b10 x21: ffffffc009c16b28 [ 0.393668] x20: ffffffc009e53861 x19: ffffff80f77fbf40 x18: 00000000d744fcc9 [ 0.394842] x17: 000000000000000b x16: 00000000000001c2 x15: ffffffc009e57550 [ 0.396016] x14: 0000000000000000 x13: ffffffffffffffff x12: 0000000100000000 [ 0.397190] x11: 0000000000000462 x10: ffffff8040258008 x9 : 0000000100000000 [ 0.398364] x8 : 0000000000000000 x7 : ffffffc0093c8bf4 x6 : 0000000000000000 [ 0.399538] x5 : 0000000000000000 x4 : ffffffc00a976e40 x3 : ffffffc00810444c [ 0.400711] x2 : 0000000000000004 x1 : 0000000000000000 x0 : 0000000000000000 [ 0.401886] Call trace: [ 0.402309] __flush_work+0x12c/0x138 [ 0.402941] schedule_on_each_cpu+0x228/0x278 [ 0.403693] rcu_tasks_rude_wait_gp+0x130/0x144 [ 0.404502] rcu_tasks_kthread+0x220/0x254 [ 0.405264] kthread+0x174/0x1ac [ 0.405837] ret_from_fork+0x10/0x20 [ 0.406456] irq event stamp: 102 [ 0.406966] hardirqs last enabled at (101): [] _raw_spin_unlock_irq+0x78/0xb4 [ 0.408304] hardirqs last disabled at (102): [] el1_dbg+0x24/0x5c [ 0.409410] softirqs last enabled at (54): [] local_bh_enable+0xc/0x2c [ 0.410645] softirqs last disabled at (50): [] local_bh_disable+0xc/0x2c [ 0.411890] ---[ end trace 0000000000000000 ]--- [ 0.413000] smp: Brought up 1 node, 4 CPUs [ 0.413762] SMP: Total of 4 processors activated. [ 0.414566] CPU features: detected: 32-bit EL0 Support [ 0.415414] CPU features: detected: 32-bit EL1 Support [ 0.416278] CPU features: detected: CRC32 instructions [ 0.447021] Callback from call_rcu_tasks_rude() invoked. [ 0.506693] Callback from call_rcu_tasks() invoked. This commit therefore fixes this issue by applying a single-CPU optimization to the RCU Tasks Rude grace-period process. The key point here is that the purpose of this RCU flavor is to force a schedule on each online CPU since some past event. But the rcu_tasks_rude_wait_gp() function runs in the context of the RCU Tasks Rude's grace-period kthread, so there must already have been a context switch on the current CPU since the call to either synchronize_rcu_tasks_rude() or call_rcu_tasks_rude(). So if there is only a single CPU online, RCU Tasks Rude's grace-period kthread does not need to anything at all. It turns out that the rcu_tasks_rude_wait_gp() function's call to schedule_on_each_cpu() causes problems during early boot. During that time, there is only one online CPU, namely the boot CPU. Therefore, applying this single-CPU optimization fixes early-boot instances of this problem. Link: https://lore.kernel.org/lkml/20220210184319.25009-1-treasure4paddy@gmail.com/T/ Suggested-by: Paul E. McKenney Signed-off-by: Padmanabha Srinivasaiah Signed-off-by: Paul E. McKenney --- kernel/rcu/tasks.h | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 99cf3a13954c..b43320b149d2 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -950,6 +950,9 @@ static void rcu_tasks_be_rude(struct work_struct *work) // Wait for one rude RCU-tasks grace period. static void rcu_tasks_rude_wait_gp(struct rcu_tasks *rtp) { + if (num_online_cpus() <= 1) + return; // Fastpath for only one CPU. + rtp->n_ipis += cpumask_weight(cpu_online_mask); schedule_on_each_cpu(rcu_tasks_be_rude); } -- 2.31.1.189.g2e36527f23