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=-2.2 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 E9229C3A5A1 for ; Wed, 28 Aug 2019 13:14:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCDA22070B for ; Wed, 28 Aug 2019 13:14:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726515AbfH1NOj (ORCPT ); Wed, 28 Aug 2019 09:14:39 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:47186 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726545AbfH1NOg (ORCPT ); Wed, 28 Aug 2019 09:14:36 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1i2xmT-00045m-G8; Wed, 28 Aug 2019 15:14:33 +0200 Date: Wed, 28 Aug 2019 15:14:33 +0200 From: Sebastian Andrzej Siewior To: "Paul E. McKenney" Cc: Joel Fernandes , Scott Wood , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Juri Lelli , Clark Williams Subject: Re: [PATCH RT v2 2/3] sched: migrate_enable: Use sleeping_lock to indicate involuntary sleep Message-ID: <20190828131433.3gi4debho5zc7hgc@linutronix.de> References: <20190821231906.4224-3-swood@redhat.com> <20190823162024.47t7br6ecfclzgkw@linutronix.de> <433936e4c720e6b81f9b297fefaa592fd8a961ad.camel@redhat.com> <20190824031014.GB2731@google.com> <20190826152523.dcjbsgyyir4zjdol@linutronix.de> <20190826162945.GE28441@linux.ibm.com> <20190827092333.jp3darw7teyyw67g@linutronix.de> <20190827155306.GF26530@linux.ibm.com> <20190828092739.46mrffvzjv6v3de5@linutronix.de> <20190828125426.GO26530@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190828125426.GO26530@linux.ibm.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 2019-08-28 05:54:26 [-0700], Paul E. McKenney wrote: > On Wed, Aug 28, 2019 at 11:27:39AM +0200, Sebastian Andrzej Siewior wrote: > > On 2019-08-27 08:53:06 [-0700], Paul E. McKenney wrote: > > > Am I understanding this correctly? > > > > Everything perfect except that it is not lockdep complaining but the > > WARN_ON_ONCE() in rcu_note_context_switch(). > > This one, right? > > WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); > > Another approach would be to change that WARN_ON_ONCE(). This fix might > be too extreme, as it would suppress other issues: > > WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT_BASE) && !preempt && t->rcu_read_lock_nesting > 0); > > But maybe what is happening under the covers is that preempt is being > set when sleeping on a spinlock. Is that the case? I would like to keep that check and that is why we have: | #if defined(CONFIG_PREEMPT_RT_FULL) | sleeping_l = t->sleeping_lock; | #endif | WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0 && !sleeping_l); in -RT and ->sleeping_lock is that counter that is incremented in spin_lock(). And the only reason why sleeping_lock_inc() was used in the patch was to disable _this_ warning. > Thanx, Paul Sebastian