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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_2 autolearn=ham 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 C1352C10F14 for ; Thu, 3 Oct 2019 11:43:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 930552086A for ; Thu, 3 Oct 2019 11:43:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730060AbfJCLnX (ORCPT ); Thu, 3 Oct 2019 07:43:23 -0400 Received: from mail.kernel.org ([198.145.29.99]:34032 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730027AbfJCLnX (ORCPT ); Thu, 3 Oct 2019 07:43:23 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 05D0320830; Thu, 3 Oct 2019 11:43:20 +0000 (UTC) Date: Thu, 3 Oct 2019 07:43:19 -0400 From: Steven Rostedt To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E . McKenney" Subject: Re: [PATCH tip/core/rcu 4/8] rcu: Ensure that ->rcu_urgent_qs is set before resched IPI Message-ID: <20191003074319.2df342dd@gandalf.local.home> In-Reply-To: <20191003013305.12854-4-paulmck@kernel.org> References: <20191003013243.GA12705@paulmck-ThinkPad-P72> <20191003013305.12854-4-paulmck@kernel.org> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Wed, 2 Oct 2019 18:33:01 -0700 paulmck@kernel.org wrote: > From: "Joel Fernandes (Google)" > > The RCU-specific resched_cpu() function sends a resched IPI to the > specified CPU, which can be used to force the tick on for a given > nohz_full CPU. This is needed when this nohz_full CPU is looping in the > kernel while blocking the current grace period. However, for the tick > to actually be forced on in all cases, that CPU's rcu_data structure's > ->rcu_urgent_qs flag must be set beforehand. This commit therefore > causes rcu_implicit_dynticks_qs() to set this flag prior to invoking > resched_cpu() on a holdout nohz_full CPU. Should this be marked for stable? -- Steve > > Signed-off-by: Joel Fernandes (Google) > Signed-off-by: Paul E. McKenney > --- > kernel/rcu/tree.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 8110514..0d83b19 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1073,6 +1073,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) > if (tick_nohz_full_cpu(rdp->cpu) && > time_after(jiffies, > READ_ONCE(rdp->last_fqs_resched) + jtsq * 3)) { > + WRITE_ONCE(*ruqp, true); > resched_cpu(rdp->cpu); > WRITE_ONCE(rdp->last_fqs_resched, jiffies); > }