Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754509AbYLIPMS (ORCPT ); Tue, 9 Dec 2008 10:12:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753212AbYLIPMF (ORCPT ); Tue, 9 Dec 2008 10:12:05 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:55047 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753156AbYLIPME (ORCPT ); Tue, 9 Dec 2008 10:12:04 -0500 Subject: Re: [PATCH 1/1] sched: CPU remove deadlock fix From: Peter Zijlstra To: Brian King Cc: mingo@elte.hu, efault@gmx.de, vatsa@in.ibm.com, balbir@linux.vnet.ibm.com, linux-kernel@vger.kernel.org In-Reply-To: <1228834794.8684.6.camel@twins> References: <200812091548.mB9Fm0sm011959@d01av04.pok.ibm.com> <1228834342.8684.5.camel@twins> <1228834794.8684.6.camel@twins> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Tue, 09 Dec 2008 16:11:56 +0100 Message-Id: <1228835516.8684.7.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1954 Lines: 53 On Tue, 2008-12-09 at 15:59 +0100, Peter Zijlstra wrote: > On Tue, 2008-12-09 at 15:52 +0100, Peter Zijlstra wrote: > > On Tue, 2008-12-09 at 08:47 -0600, Brian King wrote: > > > This patch fixes a possible deadlock scenario in the CPU remove path. > > > migration_call grabs rq->lock, then wakes up everything on rq->migration_queue > > > with the lock held. Then one of the tasks on the migration queue ends up > > > calling tg_shares_up which then also tries to acquire the same rq->lock. > > > > Looks ok, does lockdep agree? > > On second thought, I'm not seeing it at all.. > > why doesn't every wakeup deadlock? because I'm blind... void __wake_up(wait_queue_head_t *q, unsigned int mode, int nr_exclusive, void *key) { unsigned long flags; spin_lock_irqsave(&q->lock, flags); __wake_up_common(q, mode, nr_exclusive, 0, key); spin_unlock_irqrestore(&q->lock, flags); } that's q->lock, not rq->lock... > > > Signed-off-by: Brian King > > > --- > > > > > > kernel/sched.c | 2 ++ > > > 1 file changed, 2 insertions(+) > > > > > > diff -puN kernel/sched.c~sched_cpu_down_deadlock_fix kernel/sched.c > > > --- linux-2.6/kernel/sched.c~sched_cpu_down_deadlock_fix 2008-12-09 08:42:09.000000000 -0600 > > > +++ linux-2.6-bjking1/kernel/sched.c 2008-12-09 08:42:09.000000000 -0600 > > > @@ -6587,7 +6587,9 @@ migration_call(struct notifier_block *nf > > > req = list_entry(rq->migration_queue.next, > > > struct migration_req, list); > > > list_del_init(&req->list); > > > + spin_unlock_irq(&rq->lock); > > > complete(&req->done); > > > + spin_lock_irq(&rq->lock); > > > } > > > spin_unlock_irq(&rq->lock); > > > break; > > > _ -- 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/