This patch change scsi mid layer to export its busy status.
Not set the busy flag, when scsi can't dispatch I/Os anymore and
needs to kill I/Os. Otherwise, request stacking drivers may hold
requests forever.


Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
---
drivers/scsi/scsi.c | 4 ++--
drivers/scsi/scsi_lib.c | 23 ++++++++++++++++++++++-
2 files changed, 24 insertions(+), 3 deletions(-)

Index: scsi-misc-2.6/drivers/scsi/scsi_lib.c
================================================== =================
--- scsi-misc-2.6.orig/drivers/scsi/scsi_lib.c
+++ scsi-misc-2.6/drivers/scsi/scsi_lib.c
@@ -459,17 +459,30 @@ static void scsi_init_cmd_errh(struct sc

void scsi_device_unbusy(struct scsi_device *sdev)
{
+ int host_congested;
struct Scsi_Host *shost = sdev->host;
unsigned long flags;

spin_lock_irqsave(shost->host_lock, flags);
shost->host_busy--;
+ if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
+ shost->host_blocked || shost->host_self_blocked ||
+ scsi_host_in_recovery(shost))
+ host_congested = 1;
+ else
+ host_congested = 0;
+
if (unlikely(scsi_host_in_recovery(shost) &&
(shost->host_failed || shost->host_eh_scheduled)))
scsi_eh_wakeup(shost);
spin_unlock(shost->host_lock);
+
spin_lock(sdev->request_queue->queue_lock);
sdev->device_busy--;
+ if (bdi_lld_congested(&sdev->request_queue->backing_dev_info) &&
+ !host_congested && sdev->device_busy < sdev->queue_depth &&
+ !sdev->device_blocked)
+ clear_bdi_lld_congested(&sdev->request_queue->backing_dev_info);
spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
}

@@ -1496,9 +1509,14 @@ static void scsi_request_fn(struct reque
* accept it.
*/
req = elv_next_request(q);
- if (!req || !scsi_dev_queue_ready(q, sdev))
+ if (!req)
break;

+ if (!scsi_dev_queue_ready(q, sdev)) {
+ set_bdi_lld_congested(&q->backing_dev_info);
+ break;
+ }
+
if (unlikely(!scsi_device_online(sdev))) {
sdev_printk(KERN_ERR, sdev,
"rejecting I/O to offline device
");
@@ -1569,6 +1587,8 @@ static void scsi_request_fn(struct reque
rtn = scsi_dispatch_cmd(cmd);
spin_lock_irq(q->queue_lock);
if(rtn) {
+ set_bdi_lld_congested(&q->backing_dev_info);
+
/* we're refusing the command; because of
* the way locks get dropped, we need to
* check here if plugging is required */
@@ -1593,6 +1613,7 @@ static void scsi_request_fn(struct reque
* later time.
*/
spin_lock_irq(q->queue_lock);
+ set_bdi_lld_congested(&q->backing_dev_info);
blk_requeue_request(q, req);
sdev->device_busy--;
if(sdev->device_busy == 0)
Index: scsi-misc-2.6/drivers/scsi/scsi.c
================================================== =================
--- scsi-misc-2.6.orig/drivers/scsi/scsi.c
+++ scsi-misc-2.6/drivers/scsi/scsi.c
@@ -862,8 +862,6 @@ void scsi_finish_command(struct scsi_cmn
struct scsi_driver *drv;
unsigned int good_bytes;

- scsi_device_unbusy(sdev);
-
/*
* Clear the flags which say that the device/host is no longer
* capable of accepting new commands. These are set in scsi_queue.c
@@ -875,6 +873,8 @@ void scsi_finish_command(struct scsi_cmn
shost->host_blocked = 0;
sdev->device_blocked = 0;

+ scsi_device_unbusy(sdev);
+
/*
* If we have valid sense information, then some kind of recovery
* must have taken place. Make a note of this.

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Hi Mike,

On Fri, 19 Sep 2008 11:06:04 -0500, Mike Christie wrote:
> Kiyoshi Ueda wrote:
> > This patch change scsi mid layer to export its busy status.
> > Not set the busy flag, when scsi can't dispatch I/Os anymore and
> > needs to kill I/Os. Otherwise, request stacking drivers may hold
> > requests forever.
> >
> >
> > Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
> > Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> > Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
> > ---
> > drivers/scsi/scsi.c | 4 ++--
> > drivers/scsi/scsi_lib.c | 23 ++++++++++++++++++++++-
> > 2 files changed, 24 insertions(+), 3 deletions(-)
> >
> > Index: scsi-misc-2.6/drivers/scsi/scsi_lib.c
> > ================================================== =================
> > --- scsi-misc-2.6.orig/drivers/scsi/scsi_lib.c
> > +++ scsi-misc-2.6/drivers/scsi/scsi_lib.c
> > @@ -459,17 +459,30 @@ static void scsi_init_cmd_errh(struct sc
> >
> > void scsi_device_unbusy(struct scsi_device *sdev)
> > {
> > + int host_congested;
> > struct Scsi_Host *shost = sdev->host;
> > unsigned long flags;
> >
> > spin_lock_irqsave(shost->host_lock, flags);
> > shost->host_busy--;
> > + if ((shost->can_queue > 0 && shost->host_busy >= shost->can_queue) ||
> > + shost->host_blocked || shost->host_self_blocked ||
> > + scsi_host_in_recovery(shost))
> > + host_congested = 1;
> > + else
> > + host_congested = 0;
> > +
>
> You might want to check if the starget busy too (scsi-misc has this but
> Jens's tree and linus do not)? The code below that I snipped from
> scsi_request_fn will set the congested bits if scsi_target_queue_ready
> returns 0, so above here you would want to clear it if it not congested
> anymore.

Yes, thank you for noticing that.
Since I was looking at scsi-misc and your target patch is in
scsi-post-merge, I overlooked it.
I'll rebase my patches and repost again.

Thanks,
Kiyoshi Ueda

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