From mboxrd@z Thu Jan 1 00:00:00 1970 From: linas@austin.ibm.com (Linas Vepstas) Subject: [PATCH] adjust use of unplug in elevator code Date: Mon, 15 Jan 2007 15:51:17 -0600 Message-ID: <20070115215117.GD13157@austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from e32.co.us.ibm.com ([32.97.110.150]:52442 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751146AbXAOVvT (ORCPT ); Mon, 15 Jan 2007 16:51:19 -0500 Content-Disposition: inline Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Jens Axboe , Chris Wright Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, Nick Piggin , Bino.Sebastian@Emulex.Com, James.Smart@Emulex.Com, rlary@us.ibm.com, Laurie.Barry@Emulex.Com, strosake@us.ibm.com, vaios.papadimitriou@Emulex.Com Hi Chris, Jens, Can you look at this, and push upstream if this looks reasonable to you? It fixes a bug I've been tripping over. --linas A flag was recently added to the elevator code to avoid performing an unplug when reuests are being re-queued. The goal of this flag was to avoid a deep recursion that can occur when re-queueing requests after a SCSI device/host reset. See http://lkml.org/lkml/2006/5/17/254 However, that fix added the flag near the bottom of a case statement, where an earlier break (in an if statement) could transport one out of the case, without setting the flag. This patch sets the flag earlier in the case statement. I re-discovered the deep recursion recently during testing; I was told that it was a known problem, and the fix to it was in the kernel I was testing. Indeed it was ... but it didn't fix the bug. With the patch below, I no longer see the bug. Signed-off by: Linas Vepstas Cc: Jens Axboe Cc: Chris Wright ---- block/elevator.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) Index: linux-2.6.20-rc4/block/elevator.c =================================================================== --- linux-2.6.20-rc4.orig/block/elevator.c 2007-01-15 14:16:03.000000000 -0600 +++ linux-2.6.20-rc4/block/elevator.c 2007-01-15 14:20:04.000000000 -0600 @@ -590,6 +590,12 @@ void elv_insert(request_queue_t *q, stru */ rq->cmd_flags |= REQ_SOFTBARRIER; + /* + * Most requeues happen because of a busy condition, + * don't force unplug of the queue for that case. + */ + unplug_it = 0; + if (q->ordseq == 0) { list_add(&rq->queuelist, &q->queue_head); break; @@ -604,11 +610,6 @@ void elv_insert(request_queue_t *q, stru } list_add_tail(&rq->queuelist, pos); - /* - * most requeues happen because of a busy condition, don't - * force unplug of the queue for that case. - */ - unplug_it = 0; break; default: