From patchwork Mon Jun 20 22:58:14 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 12888420 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 03B07C433EF for ; Mon, 20 Jun 2022 23:00:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345964AbiFTXAJ (ORCPT ); Mon, 20 Jun 2022 19:00:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346024AbiFTW7s (ORCPT ); Mon, 20 Jun 2022 18:59:48 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 36EA9193FE; Mon, 20 Jun 2022 15:58:23 -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 ams.source.kernel.org (Postfix) with ESMTPS id C76A7B8164D; Mon, 20 Jun 2022 22:58:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C16BC341D3; Mon, 20 Jun 2022 22:58:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1655765900; bh=ndfRpTTKTYzN9518AyVhDGVdAAXc4cxYGW6C8IJNndY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kyWnO3nIrl1fziSzbt+PKFDLAugvUKcC3qn3ZIYJ5eQApUnWy1xqzbdvjH/Z0iN4b txqKxtoWnnyfCTG6TdecfWzDqdsfOxbra7E1ylzh+opqkMLQElyJvq06bN1GgDnknh b4/00CjPZmSUWh1yLDsTWJ+jnuSLVF+Iri2yRXns96Kj4l/IIa72BumFvy2BTLm5t4 AwM+FhScecn5w30eXeGqSRiFtFQ685k9kqQWutGfe76NgPfBTQ2nODqKHLL4Syk7wn k2LVXAbMjKIUyQoU2bkjmT7yYiZkT2qs80PqdHCnGV+92a4qS0ue4UyroS626P8vAa fyWusP1fxImFw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id A569B5C0D1B; Mon, 20 Jun 2022 15:58:19 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Frederic Weisbecker , "Paul E . McKenney" Subject: [PATCH rcu 09/12] rcutorture: Fix ksoftirqd boosting timing and iteration Date: Mon, 20 Jun 2022 15:58:14 -0700 Message-Id: <20220620225817.3843106-9-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220620225814.GA3842995@paulmck-ThinkPad-P17-Gen-1> References: <20220620225814.GA3842995@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Frederic Weisbecker The RCU priority boosting can fail in two situations: 1) If (nr_cpus= > maxcpus=), which means if the total number of CPUs is higher than those brought online at boot, then torture_onoff() may later bring up CPUs that weren't online on boot. Now since rcutorture initialization only boosts the ksoftirqds of the CPUs that have been set online on boot, the CPUs later set online by torture_onoff won't benefit from the boost, making RCU priority boosting fail. 2) The ksoftirqd kthreads are boosted after the creation of rcu_torture_boost() kthreads, which opens a window large enough for these rcu_torture_boost() kthreads to wait (despite running at FIFO priority) for ksoftirqds that are still running at SCHED_NORMAL priority. The issues can trigger for example with: ./kvm.sh --configs TREE01 --kconfig "CONFIG_RCU_BOOST=y" [ 34.968561] rcu-torture: !!! [ 34.968627] ------------[ cut here ]------------ [ 35.014054] WARNING: CPU: 4 PID: 114 at kernel/rcu/rcutorture.c:1979 rcu_torture_stats_print+0x5ad/0x610 [ 35.052043] Modules linked in: [ 35.069138] CPU: 4 PID: 114 Comm: rcu_torture_sta Not tainted 5.18.0-rc1 #1 [ 35.096424] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-0-g155821a-rebuilt.opensuse.org 04/01/2014 [ 35.154570] RIP: 0010:rcu_torture_stats_print+0x5ad/0x610 [ 35.198527] Code: 63 1b 02 00 74 02 0f 0b 48 83 3d 35 63 1b 02 00 74 02 0f 0b 48 83 3d 21 63 1b 02 00 74 02 0f 0b 48 83 3d 0d 63 1b 02 00 74 02 <0f> 0b 83 eb 01 0f 8e ba fc ff ff 0f 0b e9 b3 fc ff f82 [ 37.251049] RSP: 0000:ffffa92a0050bdf8 EFLAGS: 00010202 [ 37.277320] rcu: De-offloading 8 [ 37.290367] RAX: 0000000000000000 RBX: 0000000000000001 RCX: 0000000000000001 [ 37.290387] RDX: 0000000000000000 RSI: 00000000ffffbfff RDI: 00000000ffffffff [ 37.290398] RBP: 000000000000007b R08: 0000000000000000 R09: c0000000ffffbfff [ 37.290407] R10: 000000000000002a R11: ffffa92a0050bc18 R12: ffffa92a0050be20 [ 37.290417] R13: ffffa92a0050be78 R14: 0000000000000000 R15: 000000000001bea0 [ 37.290427] FS: 0000000000000000(0000) GS:ffff96045eb00000(0000) knlGS:0000000000000000 [ 37.290448] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 37.290460] CR2: 0000000000000000 CR3: 000000001dc0c000 CR4: 00000000000006e0 [ 37.290470] Call Trace: [ 37.295049] [ 37.295065] ? preempt_count_add+0x63/0x90 [ 37.295095] ? _raw_spin_lock_irqsave+0x12/0x40 [ 37.295125] ? rcu_torture_stats_print+0x610/0x610 [ 37.295143] rcu_torture_stats+0x29/0x70 [ 37.295160] kthread+0xe3/0x110 [ 37.295176] ? kthread_complete_and_exit+0x20/0x20 [ 37.295193] ret_from_fork+0x22/0x30 [ 37.295218] Fix this with boosting the ksoftirqds kthreads from the boosting hotplug callback itself and before the boosting kthreads are created. Fixes: ea6d962e80b6 ("rcutorture: Judge RCU priority boosting on grace periods, not callbacks") Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- kernel/rcu/rcutorture.c | 28 +++++++++++++--------------- 1 file changed, 13 insertions(+), 15 deletions(-) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 64ad5305829b6..b896987c21122 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -2076,6 +2076,19 @@ static int rcutorture_booster_init(unsigned int cpu) if (boost_tasks[cpu] != NULL) return 0; /* Already created, nothing more to do. */ + // Testing RCU priority boosting requires rcutorture do + // some serious abuse. Counter this by running ksoftirqd + // at higher priority. + if (IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) { + struct sched_param sp; + struct task_struct *t; + + t = per_cpu(ksoftirqd, cpu); + WARN_ON_ONCE(!t); + sp.sched_priority = 2; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + } + /* Don't allow time recalculation while creating a new task. */ mutex_lock(&boost_mutex); rcu_torture_disable_rt_throttle(); @@ -3324,21 +3337,6 @@ rcu_torture_init(void) rcutor_hp = firsterr; if (torture_init_error(firsterr)) goto unwind; - - // Testing RCU priority boosting requires rcutorture do - // some serious abuse. Counter this by running ksoftirqd - // at higher priority. - if (IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) { - for_each_online_cpu(cpu) { - struct sched_param sp; - struct task_struct *t; - - t = per_cpu(ksoftirqd, cpu); - WARN_ON_ONCE(!t); - sp.sched_priority = 2; - sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); - } - } } shutdown_jiffies = jiffies + shutdown_secs * HZ; firsterr = torture_shutdown_init(shutdown_secs, rcu_torture_cleanup);