From patchwork Mon Jun 20 22:58:12 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: 12888418 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 E1BD3CCA480 for ; Mon, 20 Jun 2022 23:00:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345759AbiFTXAI (ORCPT ); Mon, 20 Jun 2022 19:00:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60376 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346008AbiFTW7s (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 5394819C16; 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 C694DB8164C; Mon, 20 Jun 2022 22:58:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A404C341CF; 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=lkXPYbCU6J1sMOYOFTGUNwP6b8VX52iPPeaB18M4sJs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=K+NV2xHvgTWjzhRFD6v8kuYd+nTk5kr3p1xxBKsFK530HaLi/h3o4eqmzPETv3Qfi 9tOOS/DN8WI4N88fVjdF7Ow48RAOEl8IPfpGhhrm9AY+AQxVK2gpE2TpkdXCZK6DA7 TWf20BsYspTzE914RXl1ncX9qjOq8xklNLLvi5FO1317rRz+7weDcc6/JTN+xPVUej VkMqiKPwHFTp+/U4XGnEO6gG9IDLWB9TH0sG6A8Ans/2q1ucmBh23QnnXKHO06pOYH XTwyoRoLstOOaaIcY4+hVk954GGpormi4tqSoac4yt0tUtlPdNdY40iTS1Dv1TqQYg NnfFc/NKIQHYg== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id A19455C0BCC; 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, Zqiang , "Paul E . McKenney" Subject: [PATCH rcu 07/12] rcu/rcuscale: Fix smp_processor_id()-in-preemptible warnings Date: Mon, 20 Jun 2022 15:58:12 -0700 Message-Id: <20220620225817.3843106-7-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: Zqiang Systems built with CONFIG_DEBUG_PREEMPT=y can trigger the following BUG while running the rcuscale performance test: BUG: using smp_processor_id() in preemptible [00000000] code: rcu_scale_write/69 CPU: 0 PID: 66 Comm: rcu_scale_write Not tainted 5.18.0-rc7-next-20220517-yoctodev-standard+ caller is debug_smp_processor_id+0x17/0x20 Call Trace: dump_stack_lvl+0x49/0x5e dump_stack+0x10/0x12 check_preemption_disabled+0xdf/0xf0 debug_smp_processor_id+0x17/0x20 rcu_scale_writer+0x2b5/0x580 kthread+0x177/0x1b0 ret_from_fork+0x22/0x30 Reproduction method: runqemu kvm slirp nographic qemuparams="-m 4096 -smp 8" bootparams="isolcpus=2,3 nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1 rcuscale.shutdown=false rcuscale.gp_async=true" -d The problem is that the rcu_scale_writer() kthreads fail to set the PF_NO_SETAFFINITY flags, which causes is_percpu_thread() to assume that the kthread's affinity might change at any time, thus the BUG noted above. This commit therefore causes rcu_scale_writer() to set PF_NO_SETAFFINITY in its kthread's ->flags field, thus preventing this BUG. Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney --- kernel/rcu/rcuscale.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c index 277a5bfb37d48..3ef02d4a81085 100644 --- a/kernel/rcu/rcuscale.c +++ b/kernel/rcu/rcuscale.c @@ -419,6 +419,7 @@ rcu_scale_writer(void *arg) VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started"); WARN_ON(!wdpp); set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); + current->flags |= PF_NO_SETAFFINITY; sched_set_fifo_low(current); if (holdoff)