From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755807Ab1LGNcr (ORCPT ); Wed, 7 Dec 2011 08:32:47 -0500 Received: from merlin.infradead.org ([205.233.59.134]:34070 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754820Ab1LGNcq convert rfc822-to-8bit (ORCPT ); Wed, 7 Dec 2011 08:32:46 -0500 Message-ID: <1323264728.32012.107.camel@twins> Subject: Re: [BUG -tip/sched] INFO: suspicious RCU usage From: Peter Zijlstra To: Yong Zhang Cc: linux-kernel@vger.kernel.org, mingo@elte.hu, Suresh Siddha Date: Wed, 07 Dec 2011 14:32:08 +0100 In-Reply-To: <1323264485.32012.106.camel@twins> References: <20111207073942.GA12029@zhy> <1323264485.32012.106.camel@twins> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.2.1- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org I made that --- Subject: sched, nohz: Fix missing RCU read lock From: Peter Zijlstra Date: Wed Dec 07 14:28:44 CET 2011 Yong Zhang reported: > [ INFO: suspicious RCU usage. ] > kernel/sched/fair.c:5091 suspicious rcu_dereference_check() usage! This is due to the sched_domain stuff being RCU protected and commit 0b005cf5 ("sched, nohz: Implement sched group, domain aware nohz idle load balancing") overlooking this fact. The sd variable only lives inside the for_each_domain() block, so we only need to wrap that. Cc: Suresh Siddha Reported-by: Yong Zhang Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/n/tip-gt616u9aetdzgb1oc4m6uydr@git.kernel.org --- Index: linux-2.6/kernel/sched/fair.c =================================================================== --- linux-2.6.orig/kernel/sched/fair.c +++ linux-2.6/kernel/sched/fair.c @@ -5088,23 +5088,28 @@ static inline int nohz_kick_needed(struc if (rq->nr_running >= 2) goto need_kick; + rcu_read_lock(); for_each_domain(cpu, sd) { struct sched_group *sg = sd->groups; struct sched_group_power *sgp = sg->sgp; int nr_busy = atomic_read(&sgp->nr_busy_cpus); if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1) - goto need_kick; + goto need_kick_unlock; if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight && (cpumask_first_and(nohz.idle_cpus_mask, sched_domain_span(sd)) < cpu)) - goto need_kick; + goto need_kick_unlock; if (!(sd->flags & (SD_SHARE_PKG_RESOURCES | SD_ASYM_PACKING))) break; } + rcu_read_unlock(); return 0; + +need_kick_unlock: + rcu_read_unlock(); need_kick: return 1; }