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 BBB59C3A5A1 for ; Thu, 22 Aug 2019 19:31:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F4BA21848 for ; Thu, 22 Aug 2019 19:31:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389251AbfHVTbW (ORCPT ); Thu, 22 Aug 2019 15:31:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:48852 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726319AbfHVTbW (ORCPT ); Thu, 22 Aug 2019 15:31:22 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A3981308427C; Thu, 22 Aug 2019 19:31:21 +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 46A3B600CD; Thu, 22 Aug 2019 19:31:18 +0000 (UTC) Message-ID: Subject: Re: [PATCH RT v2 3/3] rcu: Disable use_softirq on PREEMPT_RT From: Scott Wood To: Joel Fernandes Cc: Sebastian Andrzej Siewior , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, "Paul E . McKenney" , Thomas Gleixner , Peter Zijlstra , Juri Lelli , Clark Williams Date: Thu, 22 Aug 2019 14:31:17 -0500 In-Reply-To: <20190822135953.GB29841@google.com> References: <20190821231906.4224-1-swood@redhat.com> <20190821231906.4224-4-swood@redhat.com> <20190822135953.GB29841@google.com> 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 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Thu, 22 Aug 2019 19:31:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2019-08-22 at 09:59 -0400, Joel Fernandes wrote: > On Wed, Aug 21, 2019 at 06:19:06PM -0500, Scott Wood wrote: > > I think the prohibition on use_softirq can be dropped once RT gets the > > latest RCU code, but the question of what use_softirq should default > > to on PREEMPT_RT remains. > > Independent of the question of what use_softirq should default to, could > we > test RT with latest RCU code now to check if the deadlock goes away? That > way, maybe we can find any issues in current RCU that cause scheduler > deadlocks in the situation you pointed. The reason I am asking is because > recently additional commits [1] try to prevent deadlock and it'd be nice > to > ensure that other conditions are not lingering (I don't think they are but > it'd be nice to be sure). > > I am happy to do such testing myself if you want, however what does it > take > to apply the RT patchset to the latest mainline? Is it an achievable feat? I did run such a test (cherry picking all RCU patches that aren't already in RT, plus your RFC patch to rcu_read_unlock_special, rather than applying RT to current mainline) with rcutorture plus a looping kernel build overnight, and didn't see any splats with or without use_softirq. -Scott