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=-6.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, 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 5A2AAC4338F for ; Fri, 20 Aug 2021 04:11:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33AF8610E6 for ; Fri, 20 Aug 2021 04:11:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231148AbhHTEML (ORCPT ); Fri, 20 Aug 2021 00:12:11 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:43326 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229792AbhHTEML (ORCPT ); Fri, 20 Aug 2021 00:12:11 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1629432689; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=0XvUZ+5BWgTwpJh88VGaw844XRBWGMqqjISDFqgaRlY=; b=MDaRtGfUx9y8afzMzDRRb5sw1oNK6h2Tuyes/5wt+kfONyLCIrCkSvgH0f7il7n5ft7sih YcngGfpEL5qhGyoL0J9mn7yzy5cxlVU4/ZqZ7m+fHXwCLDV+QsLHuJTxbLUD4mk+GkB3jt +TwtRTJ9MJ7UjNzutn3viel+uZmZpsI= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-240-Ux-jbRLdMxOdAUcuOKHHpg-1; Fri, 20 Aug 2021 00:11:22 -0400 X-MC-Unique: Ux-jbRLdMxOdAUcuOKHHpg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CF6911008070; Fri, 20 Aug 2021 04:11:19 +0000 (UTC) Received: from ovpn-113-78.phx2.redhat.com (ovpn-113-78.phx2.redhat.com [10.3.113.78]) by smtp.corp.redhat.com (Postfix) with ESMTP id EA11A189C4; Fri, 20 Aug 2021 04:11:12 +0000 (UTC) Message-ID: <561ab28b18c31fbc221f4cb0c4df6db9b0538675.camel@redhat.com> Subject: Re: [PATCH] rcutorture: Avoid problematic critical section nesting on RT From: Scott Wood To: paulmck@kernel.org, Sebastian Andrzej Siewior Cc: Valentin Schneider , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org, linux-rt-users@vger.kernel.org, Catalin Marinas , Will Deacon , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , Frederic Weisbecker , Josh Triplett , Mathieu Desnoyers , Davidlohr Bueso , Lai Jiangshan , Joel Fernandes , Anshuman Khandual , Vincenzo Frascino , Steven Price , Ard Biesheuvel , Boqun Feng , Mike Galbraith Date: Thu, 19 Aug 2021 23:11:12 -0500 In-Reply-To: <20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1> References: <20210811201354.1976839-1-valentin.schneider@arm.com> <20210811201354.1976839-2-valentin.schneider@arm.com> <20210817121345.5iyj5epemczn3a52@linutronix.de> <20210817131741.evduh4fw7vyv2dzt@linutronix.de> <20210817144018.nqssoq475vitrqlv@linutronix.de> <20210818224651.GY4126399@paulmck-ThinkPad-P17-Gen-1> <20210819153927.clqxr4f7qegpflbr@linutronix.de> <20210819154708.3efz6jtgwtuhpeds@linutronix.de> <20210819182035.GF4126399@paulmck-ThinkPad-P17-Gen-1> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Thu, 2021-08-19 at 11:20 -0700, Paul E. McKenney wrote: > On Thu, Aug 19, 2021 at 05:47:08PM +0200, Sebastian Andrzej Siewior wrote: > > On 2021-08-19 17:39:29 [+0200], To Paul E. McKenney wrote: > > > + /* > > > + * Ideally these sequences would be detected in debug builds > > > + * (regardless of RT), but until then don't stop testing > > > + * them on non-RT. > > > + */ > > > + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { > > > + /* > > > + * Can't release the outermost rcu lock in an irq disabled > > > + * section without preemption also being disabled, if irqs > > > + * had ever been enabled during this RCU critical section > > > + * (could leak a special flag and delay reporting the qs). > > > + */ > > > + if ((oldmask & RCUTORTURE_RDR_RCU) && > > > + (mask & RCUTORTURE_RDR_IRQ) && > > > + !(mask & preempts)) > > > + mask |= RCUTORTURE_RDR_RCU; > > > > This piece above, I don't understand. I had it running for a while and > > it didn't explode. Let me try TREE01 for 30min without that piece. > > This might be historical. There was a time when interrupts being > disabled across rcu_read_unlock() meant that preemption had to have > been disabled across the entire RCU read-side critical section. > > I am not seeing a purpose for it now, but I could easily be missing > something, especially given my tenuous grasp of RT. Yeah, I think this was to deal with not having the irq work stuff in RT at the time. -Scott