From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756186Ab1LWA1g (ORCPT ); Thu, 22 Dec 2011 19:27:36 -0500 Received: from mga03.intel.com ([143.182.124.21]:50183 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753817Ab1LWA1c (ORCPT ); Thu, 22 Dec 2011 19:27:32 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="88765633" Subject: Re: [patch 1/2]scsi: scsi_run_queue() doesn't use local list to handle starved sdev From: Shaohua Li To: James Bottomley Cc: lkml , "linux-scsi@vger.kernel.org" , Jens Axboe , Christoph Hellwig , "Ted Ts'o" , "Wu, Fengguang" , "Darrick J. Wong" In-Reply-To: <1324578449.9709.15.camel@dabdike.int.hansenpartnership.com> References: <1324523412.22361.471.camel@sli10-conroe> <1324578449.9709.15.camel@dabdike.int.hansenpartnership.com> Content-Type: text/plain; charset="UTF-8" Date: Fri, 23 Dec 2011 08:40:51 +0800 Message-ID: <1324600851.22361.475.camel@sli10-conroe> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2011-12-22 at 18:27 +0000, James Bottomley wrote: > On Thu, 2011-12-22 at 11:10 +0800, Shaohua Li wrote: > > scsi_run_queue() picks off all sdev from host starved_list to a local list, > > then handle them. If there are multiple threads running scsi_run_queue(), > > the starved_list will get messed. This is quite common, because request > > rq_affinity is on by default. > > > > Signed-off-by: Shaohua Li > > --- > > drivers/scsi/scsi_lib.c | 21 ++++++++++++++------- > > 1 file changed, 14 insertions(+), 7 deletions(-) > > > > Index: linux/drivers/scsi/scsi_lib.c > > =================================================================== > > --- linux.orig/drivers/scsi/scsi_lib.c 2011-12-21 16:56:23.000000000 +0800 > > +++ linux/drivers/scsi/scsi_lib.c 2011-12-22 09:33:09.000000000 +0800 > > @@ -401,9 +401,8 @@ static inline int scsi_host_is_busy(stru > > */ > > static void scsi_run_queue(struct request_queue *q) > > { > > - struct scsi_device *sdev = q->queuedata; > > + struct scsi_device *sdev = q->queuedata, *head_sdev = NULL; > > struct Scsi_Host *shost; > > - LIST_HEAD(starved_list); > > unsigned long flags; > > > > /* if the device is dead, sdev will be NULL, so no queue to run */ > > @@ -415,9 +414,8 @@ static void scsi_run_queue(struct reques > > scsi_single_lun_run(sdev); > > > > spin_lock_irqsave(shost->host_lock, flags); > > - list_splice_init(&shost->starved_list, &starved_list); > > > > - while (!list_empty(&starved_list)) { > > + while (!list_empty(&shost->starved_list)) { > > The original reason for working from a copy instead of the original list > was that the device can end up back on the starved list because of a > variety of conditions in the HBA and so this would cause the loop not to > exit, so this piece of the patch doesn't look right to me. + /* + * the head sdev is no longer starved and removed from the + * starved list, select a new sdev as head. + */ + if (head_sdev == sdev && list_empty(&sdev->starved_entry)) + head_sdev = NULL; I had this in the loop, which is to guarantee the loop will exit if a device is removed from the starved list. Thanks, Shaohua