Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758012Ab2JXJkV (ORCPT ); Wed, 24 Oct 2012 05:40:21 -0400 Received: from casper.infradead.org ([85.118.1.10]:57873 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754548Ab2JXJkU convert rfc822-to-8bit (ORCPT ); Wed, 24 Oct 2012 05:40:20 -0400 Message-ID: <1351071502.13456.54.camel@twins> Subject: Re: [RFC][PATCH] sched: Fix a deadlock of cpu-hotplug From: Peter Zijlstra To: Huacai Chen Cc: Ingo Molnar , linux-kernel@vger.kernel.org, Fuxin Zhang , Thomas Gleixner , "Srivatsa S. Bhat" , Tejun Heo Date: Wed, 24 Oct 2012 11:38:22 +0200 In-Reply-To: <1351070714-17676-1-git-send-email-chenhc@lemote.com> References: <1351070714-17676-1-git-send-email-chenhc@lemote.com> Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT X-Mailer: Evolution 3.2.2- Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5430 Lines: 118 On Wed, 2012-10-24 at 17:25 +0800, Huacai Chen wrote: > We found poweroff sometimes fails on our computers, so we have the > lock debug options configured. Then, when we do poweroff or take a > cpu down via cpu-hotplug, kernel complain as below. To resove this, > we modify sched_ttwu_pending(), disable the local irq when acquire > rq->lock. > > [ 83.066406] ================================= > [ 83.066406] [ INFO: inconsistent lock state ] > [ 83.066406] 3.5.0-3.lemote #428 Not tainted > [ 83.066406] --------------------------------- > [ 83.066406] inconsistent {IN-HARDIRQ-W} -> {HARDIRQ-ON-W} usage. > [ 83.066406] migration/1/7 [HC0[0]:SC0[0]:HE1:SE1] takes: > [ 83.066406] (&rq->lock){?.-.-.}, at: [] sched_ttwu_pending+0x64/0x98 > [ 83.066406] {IN-HARDIRQ-W} state was registered at: > [ 83.066406] [] __lock_acquire+0x80c/0x1cc0 > [ 83.066406] [] lock_acquire+0x60/0x9c > [ 83.066406] [] _raw_spin_lock+0x3c/0x50 > [ 83.066406] [] scheduler_tick+0x48/0x178 > [ 83.066406] [] update_process_times+0x54/0x70 > [ 83.066406] [] tick_handle_periodic+0x2c/0x9c > [ 83.066406] [] c0_compare_interrupt+0x8c/0x94 > [ 83.066406] [] handle_irq_event_percpu+0x7c/0x248 > [ 83.066406] [] handle_percpu_irq+0x8c/0xc0 > [ 83.066406] [] generic_handle_irq+0x48/0x58 > [ 83.066406] [] do_IRQ+0x18/0x24 > [ 83.066406] [] mach_irq_dispatch+0xe4/0x124 > [ 83.066406] [] ret_from_irq+0x0/0x4 > [ 83.066406] [] console_unlock+0x3e8/0x4c0 > [ 83.066406] [] con_init+0x370/0x398 > [ 83.066406] [] console_init+0x34/0x50 > [ 83.066406] [] start_kernel+0x2f8/0x4e0 > [ 83.066406] irq event stamp: 971 > [ 83.066406] hardirqs last enabled at (971): [] local_flush_tlb_all+0x134/0x17c > [ 83.066406] hardirqs last disabled at (970): [] local_flush_tlb_all+0x48/0x17c > [ 83.066406] softirqs last enabled at (0): [] copy_process+0x510/0x117c > [ 83.066406] softirqs last disabled at (0): [< (null)>] (null) > [ 83.066406] > [ 83.066406] other info that might help us debug this: > [ 83.066406] Possible unsafe locking scenario: > [ 83.066406] > [ 83.066406] CPU0 > [ 83.066406] ---- > [ 83.066406] lock(&rq->lock); > [ 83.066406] > [ 83.066406] lock(&rq->lock); > [ 83.066406] > [ 83.066406] *** DEADLOCK *** > [ 83.066406] > [ 83.066406] no locks held by migration/1/7. > [ 83.066406] > [ 83.066406] stack backtrace: > [ 83.066406] Call Trace: > [ 83.066406] [] dump_stack+0x8/0x34 > [ 83.066406] [] print_usage_bug+0x2ec/0x314 > [ 83.066406] [] mark_lock+0x3fc/0x774 > [ 83.066406] [] __lock_acquire+0x8a8/0x1cc0 > [ 83.066406] [] lock_acquire+0x60/0x9c > [ 83.066406] [] _raw_spin_lock+0x3c/0x50 > [ 83.066406] [] sched_ttwu_pending+0x64/0x98 > [ 83.066406] [] migration_call+0x10c/0x2e0 > [ 83.066406] [] notifier_call_chain+0x44/0x94 > [ 83.066406] [] __cpu_notify+0x30/0x5c > [ 83.066406] [] take_cpu_down+0x5c/0x70 > [ 83.066406] [] stop_machine_cpu_stop+0x104/0x1e8 > [ 83.066406] [] cpu_stopper_thread+0x110/0x1ac > [ 83.066406] [] kthread+0x88/0x90 > [ 83.066406] [] kernel_thread_helper+0x10/0x18 Weird, that's from a CPU_DYING call, I thought those were with IRQs disabled. Look at how __stop_machine() calls the function with IRQs disabled for ! stop_machine_initialized or !SMP. Also stop_machine_cpu_stop() seems to disabled interrupts, so how do we end up calling take_cpu_down() with IRQs enabled? That simply doesn't make any sense. > Signed-off-by: Huacai Chen > --- > kernel/sched/core.c | 5 +++-- > 1 files changed, 3 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 36e2666..703754a 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1468,9 +1468,10 @@ static void sched_ttwu_pending(void) > { > struct rq *rq = this_rq(); > struct llist_node *llist = llist_del_all(&rq->wake_list); > + unsigned long flags; > struct task_struct *p; > > - raw_spin_lock(&rq->lock); > + raw_spin_lock_irqsave(&rq->lock, flags); > > while (llist) { > p = llist_entry(llist, struct task_struct, wake_entry); > @@ -1478,7 +1479,7 @@ static void sched_ttwu_pending(void) > ttwu_do_activate(rq, p, 0); > } > > - raw_spin_unlock(&rq->lock); > + raw_spin_unlock_irqrestore(&rq->lock, flags); > } > > void scheduler_ipi(void) That's wrong though, you add the cost to the common case instead of the hardly ever ran hotplug case. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/