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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 64F08C3F2CD for ; Mon, 23 Mar 2020 17:17:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 403E52072D for ; Mon, 23 Mar 2020 17:17:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584983874; bh=KcCLdSNLDw74He1EmOUNqPpOZ07dejFOpJQUk5cPJ5w=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=P0iDM/anrJdGu3EHAkpsCk1VlDydlGAXexjCcrLW+fVL75QnWcNHl7WuTk7FFwbEo gjQVuGYUItsiZ+BF5OiX3cPt8uz5J8T3dcZALyzrSxZdjviK1kb+n1tZDDXV82bc0E r8MMNMWUT+H9ahdJpIDjWMqfvbVx/BPrbbcgHE6Y= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727742AbgCWRRx (ORCPT ); Mon, 23 Mar 2020 13:17:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:50610 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727510AbgCWRRw (ORCPT ); Mon, 23 Mar 2020 13:17:52 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1F54720722; Mon, 23 Mar 2020 17:17:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1584983872; bh=KcCLdSNLDw74He1EmOUNqPpOZ07dejFOpJQUk5cPJ5w=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Y6gPuI8XMrMkQCp4S2oaerKqqo4f2OfebD1lgtLUF7jmFxiCSto8DX+b+c8pL88vL 92AYoT/zYKUTmoeprgE4JfAWCxnarhdoJd/Q+nP1iUYwHI2fyvc2kqZttnB7I7se9T furFmlhBINS8j9cYImZ/dR1A8hHUacT/j0akvGNI= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id D840F35226E4; Mon, 23 Mar 2020 10:17:51 -0700 (PDT) Date: Mon, 23 Mar 2020 10:17:51 -0700 From: "Paul E. McKenney" To: Qais Yousef Cc: Davidlohr Bueso , Josh Triplett , linux-kernel@vger.kernel.org Subject: Re: Hit WARN_ON() in rcutorture.c:1055 Message-ID: <20200323171751.GL3199@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200323154309.nah44so2556ee56g@e107158-lin.cambridge.arm.com> <20200323155731.GK3199@paulmck-ThinkPad-P72> <20200323170609.w64xrfahd2snfz6h@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200323170609.w64xrfahd2snfz6h@e107158-lin.cambridge.arm.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 23, 2020 at 05:06:10PM +0000, Qais Yousef wrote: > On 03/23/20 08:57, Paul E. McKenney wrote: > > On Mon, Mar 23, 2020 at 03:43:09PM +0000, Qais Yousef wrote: > > > Hi > > > > > > I hit the following warning while running rcutorture tests. It only happens > > > when I try to hibernate the system (arm64 Juno-r2). > > > > Hibernating the system during rcutorture tests. Now that is gutsy! ;-) > > Hehe was just a side effect of testing the cpu hotplug stuff :-) > > > > > > Let me know if you need additional info. > > > > 1. Do you need this to work? If so, please tell me your use case. > > Nope. It just happened while trying to stress the cpu hotplug series I just > posted. > > > 2. What is line 1055 of your rcutorture.c? Here is my guess: > > It's 5.6-rc6, sorry should have mentioned in the report. > > /* Cycle through nesting levels of rcu_expedite_gp() calls. */ > if (can_expedite && > !(torture_random(&rand) & 0xff & (!!expediting - 1))) { > WARN_ON_ONCE(expediting == 0 && rcu_gp_is_expedited()); > if (expediting >= 0) > rcu_expedite_gp(); > else > rcu_unexpedite_gp(); > if (++expediting > 3) > expediting = -expediting; > } else if (!can_expedite) { /* Disabled during boot, recheck. */ > > If it's something you don't care about, then I don't care about too. I just > thought I'd report it in case it uncovered something worthwhile. Well, my guess was wrong. ;-) This is instead rcutorture being surprised by the fact that RCU grace periods are expedited during the hibernate process. I could fix this particular situation, but I bet that there are a number of others, including my guess above. One approach would be to halt rcutorture testing just before hibernating and restart it just after resuming. Thoughts? Thanx, Paul