From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] as i/o hang with aacraid driver 2.6.0-test1 Date: Wed, 16 Jul 2003 15:20:36 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20030716132036.GB833@suse.de> References: <1058310172.981.7.camel@markh1.pdx.osdl.net> <1058359278.1856.8.camel@mulgrave> <20030716124549.GX833@suse.de> <1058360162.1850.15.camel@mulgrave> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from ns.virtualhost.dk ([195.184.98.160]:43400 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S270776AbTGPNFs (ORCPT ); Wed, 16 Jul 2003 09:05:48 -0400 Content-Disposition: inline In-Reply-To: <1058360162.1850.15.camel@mulgrave> List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Mark Haverkamp , Nick Piggin , Andrew Morton , Cliff White , linux-scsi On Wed, Jul 16 2003, James Bottomley wrote: > > SCSI does it right, don't worry. It's a block layer problem that we need > > to find out how to correctly make sure that we deal it. Basically > > elv_next_request() does an implicit elv_started_request(), at least that > > is what AS assumes. So request re-adds should notify the scheduler of > > that fact. > > What about exporting a more generic requeue function (perhaps one that > would take care of ending the tag)? > > Our current requeue code looks like > > if (blk_rq_tagged(req)) > blk_queue_end_tag(q, req); > __elv_add_request(q, req, 0, 0); > > which looks slightly fragile given that we have to remember to end the > tag and then call a __ function (which are usually private). Not usually private, but lockless. > If we called an explicit request requeue hook, schedulers that need to > adjust for requeueing would have a single place they could plug into? blk_insert_request() is close, but it does a little more (it's useful another place in the scsi queueing, though). How about something like this? Then I can add the 'back on queue but not completed' stuff after that. ===== drivers/block/ll_rw_blk.c 1.192 vs edited ===== --- 1.192/drivers/block/ll_rw_blk.c Sun Jul 13 14:15:43 2003 +++ edited/drivers/block/ll_rw_blk.c Wed Jul 16 15:17:23 2003 @@ -1494,6 +1494,23 @@ return rq; } +/** + * blk_requeue_request - put a request back on queue + * @q: request queue where request should be inserted + * @rq: request to be inserted + * + * Description: + * Drivers often keep queueing requests until the hardware cannot accept + * more, when that condition happens we need to put the request back + * on the queue. Must be called with queue lock held. + */ +void blk_requeue_request(request_queue_t *q, struct request *rq) +{ + if (blk_rq_tagged(rq)) + blk_queue_end_tag(q, rq); + + __elv_add_request(q, rq, 0, 0); +} /** * blk_insert_request - insert a special request in to a request queue ===== drivers/scsi/scsi_lib.c 1.99 vs edited ===== --- 1.99/drivers/scsi/scsi_lib.c Mon Jun 30 03:14:44 2003 +++ edited/drivers/scsi/scsi_lib.c Wed Jul 16 15:17:52 2003 @@ -444,22 +444,8 @@ */ static void scsi_requeue_command(struct request_queue *q, struct scsi_cmnd *cmd) { - unsigned long flags; - - spin_lock_irqsave(q->queue_lock, flags); - cmd->request->special = cmd; - if (blk_rq_tagged(cmd->request)) - blk_queue_end_tag(q, cmd->request); - - /* - * set REQ_SPECIAL - we have a command - * clear REQ_DONTPREP - we assume the sg table has been - * nuked so we need to set it up again. - */ - cmd->request->flags |= REQ_SPECIAL; cmd->request->flags &= ~REQ_DONTPREP; - __elv_add_request(q, cmd->request, 0, 0); - spin_unlock_irqrestore(q->queue_lock, flags); + blk_insert_request(cmd->request, 1, cmd); scsi_run_queue(q); } @@ -1213,9 +1199,7 @@ * later time. */ spin_lock_irq(q->queue_lock); - if (blk_rq_tagged(req)) - blk_queue_end_tag(q, req); - __elv_add_request(q, req, 0, 0); + blk_requeue_request(q, req); sdev->device_busy--; if(sdev->device_busy == 0) blk_plug_device(q); ===== include/linux/blkdev.h 1.116 vs edited ===== --- 1.116/include/linux/blkdev.h Sat Jul 5 08:52:51 2003 +++ edited/include/linux/blkdev.h Wed Jul 16 15:18:06 2003 @@ -491,6 +491,7 @@ extern struct request *blk_get_request(request_queue_t *, int, int); extern void blk_put_request(struct request *); extern void blk_insert_request(request_queue_t *, struct request *, int, void *); +extern void blk_requeue_request(request_queue_t *, struct request *); extern void blk_plug_device(request_queue_t *); extern int blk_remove_plug(request_queue_t *); extern void blk_recount_segments(request_queue_t *, struct bio *); -- Jens Axboe