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 8DD8FC433F5 for ; Sun, 20 Feb 2022 20:04:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244760AbiBTUEx (ORCPT ); Sun, 20 Feb 2022 15:04:53 -0500 Received: from mxb-00190b01.gslb.pphosted.com ([23.128.96.19]:42080 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234114AbiBTUEt (ORCPT ); Sun, 20 Feb 2022 15:04:49 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC8A14B869; Sun, 20 Feb 2022 12:04:26 -0800 (PST) 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 6651560EFB; Sun, 20 Feb 2022 20:04:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id CA597C340E8; Sun, 20 Feb 2022 20:04:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1645387465; bh=m+rT89uQz+jwHipLccYFbVmSPuL28Du43sR4r18/q0Y=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=rRLIBIgOZWPI2NLtN1M2gLanOlSF/wTWtmxxTej2D3P+sAWMiD8uNQxgp5bWjO3xV 6apYe4BMu3bQC9IKvPuYfCDhRNrYPNMjNTZq55HjRl+cYD89ZvEpJUMpUTogSafsKg 8iYkCHDnIJpqwbOrIzlSo1s9uDbd1xCBP7I2QAFTqI6oo5HjrjlCnWF63XGdg4VcT6 IrEEQrbS929otv9TWWHVQrDDFZIeXDCjFWkhe6wmHhGHWXE/5Um9Umtlnr/sI2J5Lg ofHreyksy+2yB2lzngIgnUxovYU3+ldGcI6Um+Fif9GAD2VD9fQcnwy24yR/Ndig/I ST8t4mqo24LCg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 633545C0B86; Sun, 20 Feb 2022 12:04:25 -0800 (PST) Date: Sun, 20 Feb 2022 12:04:25 -0800 From: "Paul E. McKenney" To: Padmanabha Srinivasaiah Cc: josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, tj@kernel.org, linux-rpi-kernel@lists.infradead.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] rcu-tasks: Fix race in schedule and flush work Message-ID: <20220220200425.GB4285@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220217152520.18972-1-treasure4paddy@gmail.com> <20220217174330.GR4285@paulmck-ThinkPad-P17-Gen-1> <20220220183517.GA3164@pswork> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220220183517.GA3164@pswork> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Feb 20, 2022 at 07:35:17PM +0100, Padmanabha Srinivasaiah wrote: > On Thu, Feb 17, 2022 at 09:43:30AM -0800, Paul E. McKenney wrote: > > On Thu, Feb 17, 2022 at 04:25:19PM +0100, Padmanabha Srinivasaiah wrote: > > > While booting secondary CPUs, cpus_read_[lock/unlock] 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. > > > > > > Link: https://lore.kernel.org/lkml/20220210184319.25009-1-treasure4paddy@gmail.com/T/ > > > Suggested-by: Paul E. McKenney > > > Signed-off-by: Padmanabha Srinivasaiah > > > > Thank you, Padmanabha! I have queued this with additional explanation > > in the commit log as shown below. > > Thanks paul. > > > > If you have not already tested this by repeatedly rebooting, for > > example continuously in an overnight test, could you please do so? > > (I am assuming that your system can do an automated reboot loop, so no, > > I am not asking you to stay up all night!) > > > Yes, tested and issue doesn't appear. Very good, thank you! May I add your Tested-by? Thanx, Paul > > Should this somehow recur with larger systems, in which the call starts > > with (say) five CPUs online but has trouble with the sixth CPU, there > > are several ways to address it: > > > > 1. Make cpus_read_lock() act as expected. > > > > 2. Make the first for_each_online_cpu() in schedule_on_each_cpu() > > instead be for_each_possible_cpu(), always do the INIT_WORK(), > > but invoke schedule_work_on() only if cpu_online(cpu). > > > Yes, agree and was also suggested by Tejun Heo. Will also submit same, in > other thread. > > > 3. Other ideas here, when and if. > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > commit f6823834aa2e2e581ca627238fa3ad3e0a727c08 > > Author: Padmanabha Srinivasaiah > > Date: Thu Feb 17 16:25:19 2022 +0100 > > > > rcu-tasks: Fix race in schedule and flush work > > > > 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 > > > > diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h > > index d73e32d803438..f7fdb349f8b8e 100644 > > --- a/kernel/rcu/tasks.h > > +++ b/kernel/rcu/tasks.h > > @@ -955,6 +955,9 @@ 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); > > }