From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755841Ab1LGN2n (ORCPT ); Wed, 7 Dec 2011 08:28:43 -0500 Received: from casper.infradead.org ([85.118.1.10]:38935 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755693Ab1LGN2l convert rfc822-to-8bit (ORCPT ); Wed, 7 Dec 2011 08:28:41 -0500 Message-ID: <1323264485.32012.106.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 14:28:05 +0100 In-Reply-To: <20111207073942.GA12029@zhy> References: <20111207073942.GA12029@zhy> 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 On Wed, 2011-12-07 at 15:39 +0800, Yong Zhang wrote: > =============================== > [ INFO: suspicious RCU usage. ] > ------------------------------- > /build/linux/kernel/sched/fair.c:5091 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by swapper/0/1: > #0: (&sb->s_type->i_mutex_key#2){+.+.+.}, at: [] debugfs_create_file+0x8c/0x270 > > stack backtrace: > Pid: 1, comm: swapper/0 Not tainted 3.2.0-rc1-00339-gcd490c5 #14 > Call Trace: > [] ? _raw_spin_unlock_irqrestore+0x38/0x80 > [] lockdep_rcu_suspicious+0xbf/0xe0 > [] trigger_load_balance+0x5b8/0x5c0 > [] scheduler_tick+0x104/0x160 > [] update_process_times+0x6e/0x90 > [] tick_periodic+0x2c/0x70 > [] tick_handle_periodic+0x24/0x80 > [] ? T.562+0xf7/0x170 > [] smp_apic_timer_interrupt+0x66/0x98 > [] apic_timer_interrupt+0x70/0x80 > [] ? lock_release+0xe4/0x2b0 > [] _raw_spin_unlock+0x23/0x60 > [] T.562+0xf7/0x170 > [] debugfs_create_file+0xf1/0x270 > [] trace_create_file+0x19/0x50 > [] tracer_init_debugfs+0x2bd/0x3c0 > [] ? trace_create_file+0x19/0x50 > [] ? clear_boot_tracer+0x2d/0x2d > [] do_one_initcall+0x43/0x180 > [] kernel_init+0xd0/0x156 > [] kernel_thread_helper+0x4/0x10 > [] ? finish_task_switch+0x88/0xf0 > [] ? _raw_spin_unlock_irq+0x3b/0x70 > [] ? retint_restore_args+0xe/0xe > [] ? parse_early_options+0x20/0x20 > [] ? gs_change+0xb/0xb > > Seems due to commit [0b005cf5: sched, nohz: Implement sched group, domain > aware nohz idle load balancing] I think something like the below should suffice, the sd argument only lives inside the for_each_domain() so wrapping the whole block should suffice. --- kernel/sched/fair.c | 9 +++++++-- 1 files changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6482136..a4d2b7a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5088,23 +5088,28 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu) 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; }