From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753490Ab1IDXjB (ORCPT ); Sun, 4 Sep 2011 19:39:01 -0400 Received: from e8.ny.us.ibm.com ([32.97.182.138]:46532 "EHLO e8.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752568Ab1IDXi4 (ORCPT ); Sun, 4 Sep 2011 19:38:56 -0400 Date: Sun, 4 Sep 2011 16:38:46 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , Ingo Molnar , Thomas Gleixner , Peter Zijlstra Subject: Re: [PATCH 4/4] rcu: Fix early call to rcu_irq_exit() Message-ID: <20110904233846.GO2411@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1313861452-24783-1-git-send-email-fweisbec@gmail.com> <1313861452-24783-5-git-send-email-fweisbec@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1313861452-24783-5-git-send-email-fweisbec@gmail.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Aug 20, 2011 at 07:30:52PM +0200, Frederic Weisbecker wrote: > On the irq exit path, tick_nohz_stop_sched_tick() > may raise a softirq, which action leads to the wake up > path and select_task_rq_fair() that makes use of rcu > to iterate the domains. > > This is an illegal use of RCU because we may be in dyntick > idle mode: The rest of these look good! Thanx, Paul > [ 132.978883] =============================== > [ 132.978883] [ INFO: suspicious RCU usage. ] > [ 132.978883] ------------------------------- > [ 132.978883] kernel/sched_fair.c:1707 suspicious rcu_dereference_check() usage! > [ 132.978883] > [ 132.978883] other info that might help us debug this: > [ 132.978883] > [ 132.978883] > [ 132.978883] rcu_scheduler_active = 1, debug_locks = 0 > [ 132.978883] RCU used illegally from extended quiescent state! > [ 132.978883] 2 locks held by swapper/0: > [ 132.978883] #0: (&p->pi_lock){-.-.-.}, at: [] try_to_wake_up+0x39/0x2f0 > [ 132.978883] #1: (rcu_read_lock){.+.+..}, at: [] select_task_rq_fair+0x6a/0xec0 > [ 132.978883] > [ 132.978883] stack backtrace: > [ 132.978883] Pid: 0, comm: swapper Tainted: G W 3.0.0+ #178 > [ 132.978883] Call Trace: > [ 132.978883] [] lockdep_rcu_suspicious+0xe6/0x100 > [ 132.978883] [] select_task_rq_fair+0x749/0xec0 > [ 132.978883] [] ? select_task_rq_fair+0x6a/0xec0 > [ 132.978883] [] ? do_raw_spin_lock+0x54/0x150 > [ 132.978883] [] ? trace_hardirqs_on+0xd/0x10 > [ 132.978883] [] try_to_wake_up+0xd3/0x2f0 > [ 132.978883] [] ? ktime_get+0x68/0xf0 > [ 132.978883] [] wake_up_process+0x15/0x20 > [ 132.978883] [] raise_softirq_irqoff+0x65/0x110 > [ 132.978883] [] __hrtimer_start_range_ns+0x415/0x5a0 > [ 132.978883] [] ? do_raw_spin_unlock+0x5e/0xb0 > [ 132.978883] [] hrtimer_start+0x18/0x20 > [ 132.978883] [] tick_nohz_stop_sched_tick+0x393/0x450 > [ 132.978883] [] irq_exit+0xd2/0x100 > [ 132.978883] [] do_IRQ+0x66/0xe0 > [ 132.978883] [] common_interrupt+0x13/0x13 > [ 132.978883] [] ? native_safe_halt+0xb/0x10 > [ 132.978883] [] ? trace_hardirqs_on+0xd/0x10 > [ 132.978883] [] default_idle+0xba/0x370 > [ 132.978883] [] amd_e400_idle+0x5e/0x130 > [ 132.978883] [] cpu_idle+0xb6/0x120 > [ 132.978883] [] rest_init+0xef/0x150 > [ 132.978883] [] ? rest_init+0x52/0x150 > [ 132.978883] [] start_kernel+0x3da/0x3e5 > [ 132.978883] [] x86_64_start_reservations+0x131/0x135 > [ 132.978883] [] x86_64_start_kernel+0x103/0x112 > > Fix this by calling rcu_irq_exit() after tick_nohz_stop_sched_tick(). > > Signed-off-by: Frederic Weisbecker > Cc: Paul E. McKenney > Cc: Ingo Molnar > Cc: Thomas Gleixner > Cc: Peter Zijlstra > --- > kernel/softirq.c | 2 +- > 1 files changed, 1 insertions(+), 1 deletions(-) > > diff --git a/kernel/softirq.c b/kernel/softirq.c > index fca82c3..d4047b8 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -347,12 +347,12 @@ void irq_exit(void) > if (!in_interrupt() && local_softirq_pending()) > invoke_softirq(); > > - rcu_irq_exit(); > #ifdef CONFIG_NO_HZ > /* Make sure that timer wheel updates are propagated */ > if (idle_cpu(smp_processor_id()) && !in_interrupt() && !need_resched()) > tick_nohz_stop_sched_tick(0); > #endif > + rcu_irq_exit(); > preempt_enable_no_resched(); > } > > -- > 1.7.5.4 >