From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hannes Reinecke Subject: Re: Deadlock during multipath failover Date: Thu, 12 Feb 2009 14:25:33 +0100 Message-ID: <4994234D.1000404@suse.de> References: <20090212094022.GA4973@schmichrtp.de.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from mail.suse.de ([195.135.220.2]:53123 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757681AbZBLNZg (ORCPT ); Thu, 12 Feb 2009 08:25:36 -0500 In-Reply-To: <20090212094022.GA4973@schmichrtp.de.ibm.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Christof Schmitt Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org Hi Christof, Christof Schmitt wrote: > During failover tests on a current distribution kernel, we found this > problem. From reading the code, the upstream kernel has the same > problem: >=20 > During multipath failover tests with SCSI on System z, the kernel > deadlocks in this situation: >=20 >> STACK: >> 0 blk_add_timer+206 [0x2981ea] >> 1 blk_rq_timed_out+132 [0x2982a8] >> 2 blk_abort_request+114 [0x29833e] >> 3 blk_abort_queue+92 [0x2983a8] >> 4 deactivate_path+74 [0x3e00009625a] >> 5 run_workqueue+236 [0x149e04] >> 6 worker_thread+294 [0x149fce] >> 7 kthread+110 [0x14f436] >> 8 kernel_thread_starter+6 [0x10941a] >=20 > blk_abort_queue takes the queue_lock with spinlock_irqsave and walks > the timer_list with list_for_each_entry_safe. Since a path to a SCSI > device just failed, the rport state is FC_PORTSTATE_BLOCKED. This > rport state triggers blk_add_timer that calls list_add_tail to move > the request to the end of timer_list. Thus, the > list_for_each_entry_safe never reaches the end of the timer_list, it > continously moves the requests to the end of the list. >=20 Hmm. That would be fixes by using list_splice() here: diff --git a/block/blk-timeout.c b/block/blk-timeout.c index a095353..67bcc3f 100644 --- a/block/blk-timeout.c +++ b/block/blk-timeout.c @@ -209,12 +209,15 @@ void blk_abort_queue(struct request_queue *q) { unsigned long flags; struct request *rq, *tmp; + LIST_HEAD(list); =20 spin_lock_irqsave(q->queue_lock, flags); =20 elv_abort_queue(q); =20 - list_for_each_entry_safe(rq, tmp, &q->timeout_list, timeout_lis= t) + list_splice_init(&q->timeout_list, &list); + + list_for_each_entry_safe(rq, tmp, &list, timeout_list) blk_abort_request(rq); =20 spin_unlock_irqrestore(q->queue_lock, flags); > The rport state FC_PORTSTATE_BLOCKED would end, when the function > fc_timeout_deleted_rport would run to remove the rport. But this > function was schedules from queue_delayed_work. The timer already > expired, but the timer function does not run, because the timer > interrupt is disabled from the spinlock_irqsave call. >=20 =2E. but this shouldn't happen anymore when using splice, as the timer will be called _after_ the irqrestore above. Cheers, Hannes --=20 Dr. Hannes Reinecke zSeries & Storage hare@suse.de +49 911 74053 688 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg GF: Markus Rex, HRB 16746 (AG N=FCrnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html