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=-0.8 required=3.0 tests=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 27F94C4CEC9 for ; Tue, 17 Sep 2019 16:32:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 02B5F20665 for ; Tue, 17 Sep 2019 16:32:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730281AbfIQQcN (ORCPT ); Tue, 17 Sep 2019 12:32:13 -0400 Received: from mx1.redhat.com ([209.132.183.28]:19362 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727788AbfIQQcN (ORCPT ); Tue, 17 Sep 2019 12:32:13 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E264169097; Tue, 17 Sep 2019 16:32:12 +0000 (UTC) Received: from ovpn-117-172.phx2.redhat.com (ovpn-117-172.phx2.redhat.com [10.3.117.172]) by smtp.corp.redhat.com (Postfix) with ESMTP id E797960923; Tue, 17 Sep 2019 16:32:11 +0000 (UTC) Message-ID: Subject: Re: [PATCH RT v3 5/5] rcutorture: Avoid problematic critical section nesting on RT From: Scott Wood To: Sebastian Andrzej Siewior Cc: Joel Fernandes , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, "Paul E . McKenney" , Thomas Gleixner , Steven Rostedt , Peter Zijlstra , Juri Lelli , Clark Williams Date: Tue, 17 Sep 2019 11:32:11 -0500 In-Reply-To: <20190917145035.l6egzthsdzp7aipe@linutronix.de> References: <20190911165729.11178-1-swood@redhat.com> <20190911165729.11178-6-swood@redhat.com> <20190912221706.GC150506@google.com> <500cabaa80f250b974409ee4a4fca59bf2e24564.camel@redhat.com> <20190917100728.wnhdvmbbzzxolef4@linutronix.de> <26dbecfee2c02456ddfda3647df1bcd56d9cc520.camel@redhat.com> <20190917145035.l6egzthsdzp7aipe@linutronix.de> Organization: Red Hat Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5 (3.30.5-1.fc29) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Tue, 17 Sep 2019 16:32:13 +0000 (UTC) Sender: linux-rt-users-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org On Tue, 2019-09-17 at 16:50 +0200, Sebastian Andrzej Siewior wrote: > On 2019-09-17 09:36:22 [-0500], Scott Wood wrote: > > > On non-RT you can (but should not) use the counter part of the > > > function > > > in random order like: > > > local_bh_disable(); > > > local_irq_disable(); > > > local_bh_enable(); > > > local_irq_enable(); > > > > Actually even non-RT will assert if you do local_bh_enable() with IRQs > > disabled -- but the other combinations do work, and are used some places > > via > > spinlocks. If they are used via direct calls to preempt_disable() or > > local_irq_disable() (or via raw spinlocks), then that will not go away > > on RT > > and we'll have a problem. > > lockdep_assert_irqs_enabled() is a nop with CONFIG_PROVE_LOCKING=N and > RT breaks either way. Right, I meant a non-RT kernel with debug checks enabled. > > > Since you _can_ use it in random order Paul wants to test that the > > > random use of those function does not break RCU in any way. Since they > > > can not be used on RT in random order it has been agreed that we keep > > > the test for !RT but disable it on RT. > > > > For now, yes. Long term it would be good to keep track of when > > preemption/irqs would be disabled on RT, even when running a non-RT > > debug > > kernel, and assert when bad things are done with it (assuming an RT- > > capable > > arch). Besides detecting these fairly unusual patterns, it could also > > detect earlier the much more common problem of nesting a non-raw > > spinlock > > inside a raw spinlock or other RT-atomic context. > > you will be surprised but we have patches for that. We need first get > rid of other "false positives" before plugging this in. Nice! Are the "false positives" real issues from components that are currently blacklisted on RT, or something different? -Scott