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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 1D651C433DB for ; Wed, 6 Jan 2021 15:45:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE45623127 for ; Wed, 6 Jan 2021 15:45:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727202AbhAFPpJ (ORCPT ); Wed, 6 Jan 2021 10:45:09 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727115AbhAFPpI (ORCPT ); Wed, 6 Jan 2021 10:45:08 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 58231C061357 for ; Wed, 6 Jan 2021 07:44:28 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=gtC4c3Ej8bBFZ9FcoprvJDs27X+S4qSFCKOgvJeaiHM=; b=VLYD91MY/OSoQtdL9IqCVn5DlF XFRILKWh6jpGCxrycvhxLiQxbYYgN4zeSMSkYsa/2mcx4b+kuqZ+XCQ6sMBEJh0AfhPkoXH+e81N/ 6yUxRmU0VnsmtL4Dqf1jUBSvFiR+NatVuEkPvfLWyJC1DFknjET/KtlLkDncIG3kzGCIii92aB9Vi WnHlh4eblDRL9uXglZ+D/+MCyseodVhJirB81YNVZYJOfBobzqRpB+Fvvgm2spI3+DYHkEoEmnMmO f9n8P5VI+xf27h1hJE2IiqvlJGIvHpZJP+Y4JKKh1qJcstnCSdxj3DS8mrsvB6TLHwjCnkreLX+ub rfiuxm0Q==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kxAz1-0002U2-CA; Wed, 06 Jan 2021 15:44:23 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id DDA69305C10; Wed, 6 Jan 2021 16:44:21 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A41A42029C723; Wed, 6 Jan 2021 16:44:21 +0100 (CET) Date: Wed, 6 Jan 2021 16:44:21 +0100 From: Peter Zijlstra To: "Paul E. McKenney" Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, valentin.schneider@arm.com, bristot@redhat.com, frederic@kernel.org Subject: Re: lockdep splat in v5.11-rc1 involving console_sem and rq locks Message-ID: References: <20210105220115.GA27357@paulmck-ThinkPad-P72> <20210106144621.GJ17086@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210106144621.GJ17086@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 06, 2021 at 06:46:21AM -0800, Paul E. McKenney wrote: > Huh. The WARN does not always generate the lockdep complaint. But > fair enough. Any printk()/WARN/BUG with rq lock held ought to generate that splat, sometimes we die before we splat. The printk rewrite should eventually fix that. > > https://lkml.kernel.org/r/20201226025117.2770-1-jiangshanlai@gmail.com > > Thomas pointed me at this one a couple of weeks ago. Here is an > additional fix for rcutorture: f67e04bb0695 ("torture: Break affinity > of kthreads last running on outgoing CPU"). I am still getting WARNs > and lockdep splats with both applied. That patch looks racy, what avoids the task being shuffled right back before the CPU goes offline? > What would break if I made the code dump out a few entries in the > runqueue if the warning triggered? There was a patch around that did that, Valentin might remember where that was.