Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754680AbYLISOT (ORCPT ); Tue, 9 Dec 2008 13:14:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753673AbYLISOF (ORCPT ); Tue, 9 Dec 2008 13:14:05 -0500 Received: from mtagate5.uk.ibm.com ([195.212.29.138]:42465 "EHLO mtagate5.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753573AbYLISOD (ORCPT ); Tue, 9 Dec 2008 13:14:03 -0500 Date: Tue, 9 Dec 2008 19:12:36 +0100 From: Heiko Carstens To: Brian King Cc: mingo@elte.hu, a.p.zijlstra@chello.nl, efault@gmx.de, vatsa@in.ibm.com, balbir@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, Nick Piggin Subject: Re: [PATCH 1/1] sched: CPU remove deadlock fix Message-ID: <20081209181236.GA4432@osiris.boeblingen.de.ibm.com> References: <200812091548.mB9Fm0sm011959@d01av04.pok.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200812091548.mB9Fm0sm011959@d01av04.pok.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2457 Lines: 53 On Tue, Dec 09, 2008 at 08:47:00AM -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. > > [c000000058eab2e0] c000000000502078 ._spin_lock_irqsave+0x98/0xf0 > [c000000058eab370] c00000000008011c .tg_shares_up+0x10c/0x20c > [c000000058eab430] c00000000007867c .walk_tg_tree+0xc4/0xfc > [c000000058eab4d0] c0000000000840c8 .try_to_wake_up+0xb0/0x3c4 > [c000000058eab590] c0000000000799a0 .__wake_up_common+0x6c/0xe0 > [c000000058eab640] c00000000007ada4 .complete+0x54/0x80 > [c000000058eab6e0] c000000000509fa8 .migration_call+0x5fc/0x6f8 > [c000000058eab7c0] c000000000504074 .notifier_call_chain+0x68/0xe0 > [c000000058eab860] c000000000506568 ._cpu_down+0x2b0/0x3f4 > [c000000058eaba60] c000000000506750 .cpu_down+0xa4/0x108 > [c000000058eabb10] c000000000507e54 .store_online+0x44/0xa8 > [c000000058eabba0] c000000000396260 .sysdev_store+0x3c/0x50 > [c000000058eabc10] c0000000001a39b8 .sysfs_write_file+0x124/0x18c > [c000000058eabcd0] c00000000013061c .vfs_write+0xd0/0x1bc > [c000000058eabd70] c0000000001308a4 .sys_write+0x68/0x114 > [c000000058eabe30] c0000000000086b4 syscall_exit+0x0/0x40 > > 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; I've seen the same deadlock on s390 and had a similar fix, but no testing yet. Thanks for the fix! :) Will this be in 2.6.28? -- 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/