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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,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 41D12C3A5A2 for ; Fri, 23 Aug 2019 19:46:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0E00121874 for ; Fri, 23 Aug 2019 19:46:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391734AbfHWTqq (ORCPT ); Fri, 23 Aug 2019 15:46:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:18852 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732627AbfHWTqp (ORCPT ); Fri, 23 Aug 2019 15:46:45 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 8A5F3C08C33E; Fri, 23 Aug 2019 19:46:45 +0000 (UTC) Received: from ovpn-117-150.phx2.redhat.com (ovpn-117-150.phx2.redhat.com [10.3.117.150]) by smtp.corp.redhat.com (Postfix) with ESMTP id DFACF5C578; Fri, 23 Aug 2019 19:46:39 +0000 (UTC) Message-ID: <40dd3a7e37ed9b3d03c50221dafc7aa137827ce8.camel@redhat.com> Subject: Re: [PATCH RT v2 1/3] rcu: Acquire RCU lock when disabling BHs From: Scott Wood To: Sebastian Andrzej Siewior Cc: Joel Fernandes , "Paul E. McKenney" , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Juri Lelli , Clark Williams Date: Fri, 23 Aug 2019 14:46:39 -0500 In-Reply-To: <20190823161740.xhntflxs3vlf3xnu@linutronix.de> References: <20190821231906.4224-1-swood@redhat.com> <20190821231906.4224-2-swood@redhat.com> <20190821233358.GU28441@linux.ibm.com> <20190822133955.GA29841@google.com> <20190823161740.xhntflxs3vlf3xnu@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 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Fri, 23 Aug 2019 19:46:45 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2019-08-23 at 18:17 +0200, Sebastian Andrzej Siewior wrote: > On 2019-08-22 22:23:23 [-0500], Scott Wood wrote: > > On Thu, 2019-08-22 at 09:39 -0400, Joel Fernandes wrote: > > > On Wed, Aug 21, 2019 at 04:33:58PM -0700, Paul E. McKenney wrote: > > > > On Wed, Aug 21, 2019 at 06:19:04PM -0500, Scott Wood wrote: > > > > > Signed-off-by: Scott Wood > > > > > --- > > > > > Another question is whether non-raw spinlocks are intended to > > > > > create > > > > > an > > > > > RCU read-side critical section due to implicit preempt disable. > > > > > > > > Hmmm... Did non-raw spinlocks act like rcu_read_lock_sched() > > > > and rcu_read_unlock_sched() pairs in -rt prior to the RCU flavor > > > > consolidation? If not, I don't see why they should do so after that > > > > consolidation in -rt. > > > > > > May be I am missing something, but I didn't see the connection between > > > consolidation and this patch. AFAICS, this patch is so that > > > rcu_read_lock_bh_held() works at all on -rt. Did I badly miss > > > something? > > > > Before consolidation, RT mapped rcu_read_lock_bh_held() to > > rcu_read_lock_bh() and called rcu_read_lock() from > > rcu_read_lock_bh(). This > > somehow got lost when rebasing on top of 5.0. > > so now rcu_read_lock_bh_held() is untouched and in_softirq() reports 1. > So the problem is that we never hold RCU but report 1 like we do? Yes. -Scott