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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 BB56AC4CEC9 for ; Tue, 17 Sep 2019 14:50:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 964BC214AF for ; Tue, 17 Sep 2019 14:50:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728670AbfIQOuj (ORCPT ); Tue, 17 Sep 2019 10:50:39 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:42118 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727708AbfIQOuj (ORCPT ); Tue, 17 Sep 2019 10:50:39 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1iAEoN-0008Sa-Pj; Tue, 17 Sep 2019 16:50:35 +0200 Date: Tue, 17 Sep 2019 16:50:35 +0200 From: Sebastian Andrzej Siewior To: Scott Wood 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 Subject: Re: [PATCH RT v3 5/5] rcutorture: Avoid problematic critical section nesting on RT Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <26dbecfee2c02456ddfda3647df1bcd56d9cc520.camel@redhat.com> User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > > 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. > -Scott Sebastian