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 49349C3A5A1 for ; Wed, 28 Aug 2019 09:27:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1DBCC217F5 for ; Wed, 28 Aug 2019 09:27:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726432AbfH1J1n (ORCPT ); Wed, 28 Aug 2019 05:27:43 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:46220 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726339AbfH1J1n (ORCPT ); Wed, 28 Aug 2019 05:27:43 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1i2uEt-0006qQ-MY; Wed, 28 Aug 2019 11:27:39 +0200 Date: Wed, 28 Aug 2019 11:27:39 +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: <20190828092739.46mrffvzjv6v3de5@linutronix.de> References: <20190821231906.4224-1-swood@redhat.com> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190827155306.GF26530@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 2019-08-27 08:53:06 [-0700], Paul E. McKenney wrote: > > > On the other hand, within a PREEMPT=n kernel, the call to schedule() > > > would split even an rcu_read_lock() critical section. Which is why I > > > asked earlier if sleeping_lock_inc() and sleeping_lock_dec() are no-ops > > > in !PREEMPT_RT_BASE kernels. We would after all want the usual lockdep > > > complaints in that case. > > > > sleeping_lock_inc() +dec() is only RT specific. It is part of RT's > > spin_lock() implementation and used by RCU (rcu_note_context_switch()) > > to not complain if invoked within a critical section. > > Then this is being called when we have something like this, correct? > > DEFINE_SPINLOCK(mylock); // As opposed to DEFINE_RAW_SPINLOCK(). > > ... > > rcu_read_lock(); > do_something(); > spin_lock(&mylock); // Can block in -rt, thus needs sleeping_lock_inc() > ... > rcu_read_unlock(); > > Without sleeping_lock_inc(), lockdep would complain about a voluntary > schedule within an RCU read-side critical section. But in -rt, voluntary > schedules due to sleeping on a "spinlock" are OK. > > Am I understanding this correctly? Everything perfect except that it is not lockdep complaining but the WARN_ON_ONCE() in rcu_note_context_switch(). > > Thanx, Paul Sebastian