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 X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38CBBC33CA9 for ; Mon, 13 Jan 2020 00:33:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F402D22314 for ; Mon, 13 Jan 2020 00:33:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387535AbgAMAdR (ORCPT ); Sun, 12 Jan 2020 19:33:17 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:57771 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387493AbgAMAdR (ORCPT ); Sun, 12 Jan 2020 19:33:17 -0500 Received: from fsav109.sakura.ne.jp (fsav109.sakura.ne.jp [27.133.134.236]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 00D0XE7i088571; Mon, 13 Jan 2020 09:33:14 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav109.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav109.sakura.ne.jp); Mon, 13 Jan 2020 09:33:14 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav109.sakura.ne.jp) Received: from [192.168.1.9] (softbank126040062084.bbtec.net [126.40.62.84]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 00D0X8lX088530 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 13 Jan 2020 09:33:14 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: [PATCH] sched/core: fix illegal RCU from offline CPUs To: Qian Cai , peterz@infradead.org, mingo@redhat.com Cc: juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, paulmck@kernel.org, tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200112161752.10492-1-cai@lca.pw> From: Tetsuo Handa Message-ID: <3ffaaf32-88b6-fdf1-c7c7-ab56292c047f@I-love.SAKURA.ne.jp> Date: Mon, 13 Jan 2020 09:33:08 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.3.1 MIME-Version: 1.0 In-Reply-To: <20200112161752.10492-1-cai@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020/01/13 1:17, Qian Cai wrote: > In the CPU-offline process, it calls mmdrop() after idle entry and the > subsequent call to cpuhp_report_idle_dead(). Once execution passes the > call to rcu_report_dead(), RCU is ignoring the CPU, which results in > lockdep complaints when mmdrop() uses RCU from either memcg or > debugobjects. Fix it by scheduling mmdrop() on another online CPU. > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 90e4b00ace89..41fb49f3dfce 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -6194,7 +6194,8 @@ void idle_task_exit(void) > current->active_mm = &init_mm; > finish_arch_post_lock_switch(); > } > - mmdrop(mm); > + smp_call_function_single(cpumask_first(cpu_online_mask), > + (void (*)(void *))mmdrop, mm, 0); mmdrop() might sleep, but /* * smp_call_function_single - Run a function on a specific CPU * @func: The function to run. This must be fast and non-blocking. * @info: An arbitrary pointer to pass to the function. * @wait: If true, wait until function has completed on other CPUs. * * Returns 0 on success, else a negative status code. */ . Maybe mmdrop_async() instead?