Re: [PATCH] as i/o hang with aacraid driver 2.6.0-test1

Jens Axboe
2003-07-16T13:05:48Z

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