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 D9CB0C4CECD for ; Tue, 17 Sep 2019 14:06:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B815E21852 for ; Tue, 17 Sep 2019 14:06:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726736AbfIQOGj (ORCPT ); Tue, 17 Sep 2019 10:06:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60634 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726234AbfIQOGj (ORCPT ); Tue, 17 Sep 2019 10:06:39 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E2631300CB2C; Tue, 17 Sep 2019 14:06:38 +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 46B175D9D5; Tue, 17 Sep 2019 14:06:29 +0000 (UTC) Message-ID: <63b430ca2f067e61bef1c387fad782ab4a2c1ed3.camel@redhat.com> Subject: Re: [PATCH RT v3 1/5] rcu: Acquire RCU lock when disabling BHs From: Scott Wood To: Sebastian Andrzej Siewior Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, "Paul E . McKenney" , Joel Fernandes , Thomas Gleixner , Steven Rostedt , Peter Zijlstra , Juri Lelli , Clark Williams Date: Tue, 17 Sep 2019 09:06:28 -0500 In-Reply-To: <20190917074456.yj7t3wdwuhn3zcng@linutronix.de> References: <20190911165729.11178-1-swood@redhat.com> <20190911165729.11178-2-swood@redhat.com> <20190917074456.yj7t3wdwuhn3zcng@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 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Tue, 17 Sep 2019 14:06:39 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2019-09-17 at 09:44 +0200, Sebastian Andrzej Siewior wrote: > On 2019-09-11 17:57:25 [+0100], Scott Wood wrote: > > > > @@ -615,10 +645,7 @@ static inline void rcu_read_unlock(void) > > static inline void rcu_read_lock_bh(void) > > { > > local_bh_disable(); > > - __acquire(RCU_BH); > > - rcu_lock_acquire(&rcu_bh_lock_map); > > - RCU_LOCKDEP_WARN(!rcu_is_watching(), > > - "rcu_read_lock_bh() used illegally while idle"); > > + rcu_bh_lock_acquire(); > > } > > > > /* > > I asked previously why do you need to change rcu_read_lock_bh() and you > replied that you don't remember: > > https://lore.kernel.org/linux-rt-users/b948ec6cccda31925ed8dc123bd0f55423fff3d4.camel@redhat.com/ > > Did this change? Sorry, I missed that you were asking about rcu_read_lock_bh() as well. I did remove the change to rcu_read_lock_bh_held(). With this patch, local_bh_disable() calls rcu_read_lock() on RT which handles this debug stuff. Doing it twice shouldn't be explicitly harmful, but it's redundant, and debug kernels are slow enough as is. -Scott