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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED 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 E18E2C43387 for ; Thu, 10 Jan 2019 17:11:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2ADA20874 for ; Thu, 10 Jan 2019 17:11:58 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=efficios.com header.i=@efficios.com header.b="dTwzf+GA" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729434AbfAJRL5 (ORCPT ); Thu, 10 Jan 2019 12:11:57 -0500 Received: from mail.efficios.com ([167.114.142.138]:47150 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729390AbfAJRL5 (ORCPT ); Thu, 10 Jan 2019 12:11:57 -0500 Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id 374A4AF4E5; Thu, 10 Jan 2019 12:11:56 -0500 (EST) Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10032) with ESMTP id 7pptXIhLtyaG; Thu, 10 Jan 2019 12:11:55 -0500 (EST) Received: from localhost (ip6-localhost [IPv6:::1]) by mail.efficios.com (Postfix) with ESMTP id A6D0CAF4DE; Thu, 10 Jan 2019 12:11:55 -0500 (EST) DKIM-Filter: OpenDKIM Filter v2.10.3 mail.efficios.com A6D0CAF4DE DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=efficios.com; s=default; t=1547140315; bh=kZSmyay1d5c2mhy8Cf7ox6oAbf9TKQ+v011C3uWWyQY=; h=Date:From:To:Message-ID:MIME-Version; b=dTwzf+GAQEYzCIRBYVKShqkL37N0xng7E/l8PfSQbFsT6y/nYm/NokIsxVP2wLfZN GxZAS2zRc9G+CE073xMWoa+kjdnmIQCsXzgxISEu3LfaWRn6RinRbTkDFXwnC3He5o B0eLnVWMpHq7o0mNXOdduDq1e9VuH6MoNCKsQPewm76gaiFZvmBMnImDBcKpMFla0L mHNn8cyqsHYeBHur0d3J6xNZVN3y5Ndp4vd08lwzyPXfl82r7wDd9xVLk8RXE7Qwmw vxKN3rXbJVrWpO0mxQVv398xW2SHtdO7gqqMkNbeXH2VhyhDIvzGQ0qxasRRjiqRyC bgcbQj/zRFuzA== X-Virus-Scanned: amavisd-new at efficios.com Received: from mail.efficios.com ([IPv6:::1]) by localhost (mail02.efficios.com [IPv6:::1]) (amavisd-new, port 10026) with ESMTP id p6Zh1nIHVw2F; Thu, 10 Jan 2019 12:11:55 -0500 (EST) Received: from mail02.efficios.com (mail02.efficios.com [167.114.142.138]) by mail.efficios.com (Postfix) with ESMTP id 938E7AF4D4; Thu, 10 Jan 2019 12:11:55 -0500 (EST) Date: Thu, 10 Jan 2019 12:11:55 -0500 (EST) From: Mathieu Desnoyers To: rostedt Cc: "Paul E. McKenney" , linux-kernel , Peter Zijlstra Message-ID: <600900741.1177.1547140315581.JavaMail.zimbra@efficios.com> In-Reply-To: <1884815641.993.1547138653377.JavaMail.zimbra@efficios.com> References: <2103471967.794.1547084331086.JavaMail.zimbra@efficios.com> <20190110110839.7daeef3d@gandalf.local.home> <1884815641.993.1547138653377.JavaMail.zimbra@efficios.com> Subject: Re: Possible use of RCU while in extended QS: idle vs RCU read-side in interrupt vs rcu_eqs_exit MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Originating-IP: [167.114.142.138] X-Mailer: Zimbra 8.8.10_GA_3716 (ZimbraWebClient - FF52 (Linux)/8.8.10_GA_3745) Thread-Topic: Possible use of RCU while in extended QS: idle vs RCU read-side in interrupt vs rcu_eqs_exit Thread-Index: 27wp/p4E6gUF7FLK8PORZvci3aR5Z84PIFV8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ----- On Jan 10, 2019, at 8:44 AM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote: > ----- On Jan 10, 2019, at 8:08 AM, rostedt rostedt@goodmis.org wrote: > >> On Wed, 9 Jan 2019 20:38:51 -0500 (EST) >> Mathieu Desnoyers wrote: >> >>> Hi Paul, >>> >>> I've had a user report that trace_sched_waking() appears to be >>> invoked while !rcu_is_watching() in some situation, so I started >>> digging into the scheduler idle code. >> >> I'm wondering if this isn't a bug. Do you have the backtrace for where >> trace_sched_waking() was called without rcu watching? > > I strongly suspect a bug as well. I'm awaiting a reproducer from the > user whom reported this issue so I can add a WARN_ON_ONCE(!rcu_is_watching()) > in the scheduler code near trace_sched_waking() and gather a backtrace. > > It still has to be confirmed, but I suspect this have been triggered > within a HyperV guest. It may therefore be related to a virtualized environment. > > I'll try to ask more specifically on which environment this was encountered. So it ends up it happens directly on hardware on a Linux laptop. Here is the stacktrace: vmlinux!try_to_wake_up vmlinux!default_wake_function vmlinux!pollwake vmlinux!__wake_up_common vmlinux!__wake_up_common_lock vmlinux!__wake_up vmlinux!perf_event_wakeup vmlinux!perf_pending_event vmlinux!irq_work_run_list vmlinux!irq_work_run vmlinux!smp_irq_work_iterrupt vmlinux!irq_work_interrupt vmlinux!finish_task_switch vmlinux!__schedule vmlinux!schedule_idle vmlinux!do_idle vmlinux!cpu_startup_entry vmlinux!start_secondary vmlinux!secondary_startup_64 Does it raise any red flag ? Thanks, Mathieu > > Thanks, > > Mathieu > >> >> -- Steve >> >>> >>> It appears that interrupts are re-enabled before rcu_eqs_exit() is >>> invoked when exiting idle code from the scheduler. >>> >>> I wonder what happens if an interrupt handler (including scheduler code) >>> happens to issue a RCU read-side critical section before rcu_eqs_exit() >>> is called ? Is there some code on interrupt entry that ensures rcu eqs >>> state is exited in such scenario ? >>> >>> Thanks, >>> >>> Mathieu > > -- > Mathieu Desnoyers > EfficiOS Inc. > http://www.efficios.com -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com