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Date: Thu, 25 Sep 2008 11:55:33 -0400 (EDT)
From: Kiyoshi Ueda <k-ueda@...jp.nec.com>
To: akpm@...ux-foundation.org, jens.axboe@...cle.com,
James.Bottomley@...senPartnership.com
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
dm-devel@...hat.com, j-nomura@...jp.nec.com, k-ueda@...jp.nec.com
Subject: [RFC PATCH 2/2] scsi: export busy state via q->lld_busy_fn()
This patch implements q->lld_busy_fn() for scsi mid layer to export
its busy state.
Please note that it checks the cached information (sdev->lld_busy)
for efficiency, instead of checking the actual state of
sdev/starget/shost everytime.
So the care must be taken not to leave sdev->lld_busy = 1 for
the following cases:
- when there is no request in the sdev queue
- when scsi can't dispatch I/Os anymore and needs to kill I/Os
Otherwise, request stacking drivers may not submit any request,
and then, nobody sets back lld_busy = 0 and that causes deadlock.
OTOH, it has no major problem in setting sdev->lld_busy = 0 even when
the starget/shost is actually busy, because newly submitted request
will soon turn it to 1 in scsi_request_fn().
Signed-off-by: Kiyoshi Ueda <k-ueda@...jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@...jp.nec.com>
Cc: James Bottomley <James.Bottomley@...senPartnership.com>
---
drivers/scsi/scsi.c | 4 ++--
drivers/scsi/scsi_lib.c | 20 +++++++++++++++++++-
include/scsi/scsi_device.h | 13 +++++++++++++
3 files changed, 34 insertions(+), 3 deletions(-)
Index: linux-2.6-block/drivers/scsi/scsi_lib.c
===================================================================
--- linux-2.6-block.orig/drivers/scsi/scsi_lib.c
+++ linux-2.6-block/drivers/scsi/scsi_lib.c
@@ -470,6 +470,8 @@ void scsi_device_unbusy(struct scsi_devi
spin_unlock(shost->host_lock);
spin_lock(sdev->request_queue->queue_lock);
sdev->device_busy--;
+ if (sdev->device_busy < sdev->queue_depth && !sdev->device_blocked)
+ sdev->lld_busy = 0;
spin_unlock_irqrestore(sdev->request_queue->queue_lock, flags);
}
@@ -1461,6 +1463,13 @@ static void scsi_softirq_done(struct req
}
}
+static int scsi_lld_busy(struct request_queue *q)
+{
+ struct scsi_device *sdev = q->queuedata;
+
+ return sdev ? sdev->lld_busy : 0;
+}
+
/*
* Function: scsi_request_fn()
*
@@ -1503,9 +1512,14 @@ 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)) {
+ sdev->lld_busy = 1;
+ break;
+ }
+
if (unlikely(!scsi_device_online(sdev))) {
sdev_printk(KERN_ERR, sdev,
"rejecting I/O to offline device\n");
@@ -1576,6 +1590,8 @@ static void scsi_request_fn(struct reque
rtn = scsi_dispatch_cmd(cmd);
spin_lock_irq(q->queue_lock);
if(rtn) {
+ sdev->lld_busy = 1;
+
/* we're refusing the command; because of
* the way locks get dropped, we need to
* check here if plugging is required */
@@ -1600,6 +1616,7 @@ static void scsi_request_fn(struct reque
* later time.
*/
spin_lock_irq(q->queue_lock);
+ sdev->lld_busy = 1;
blk_requeue_request(q, req);
sdev->device_busy--;
if(sdev->device_busy == 0)
@@ -1683,6 +1700,7 @@ struct request_queue *scsi_alloc_queue(s
blk_queue_prep_rq(q, scsi_prep_fn);
blk_queue_softirq_done(q, scsi_softirq_done);
blk_queue_rq_timed_out(q, scsi_times_out);
+ blk_queue_lld_busy(q, scsi_lld_busy);
return q;
}
Index: linux-2.6-block/drivers/scsi/scsi.c
===================================================================
--- linux-2.6-block.orig/drivers/scsi/scsi.c
+++ linux-2.6-block/drivers/scsi/scsi.c
@@ -803,8 +803,6 @@ 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
@@ -816,6 +814,8 @@ 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.
Index: linux-2.6-block/include/scsi/scsi_device.h
===================================================================
--- linux-2.6-block.orig/include/scsi/scsi_device.h
+++ linux-2.6-block/include/scsi/scsi_device.h
@@ -143,6 +143,19 @@ struct scsi_device {
unsigned retry_hwerror:1; /* Retry HARDWARE_ERROR */
unsigned last_sector_bug:1; /* do not use multisector accesses on
SD_LAST_BUGGY_SECTORS */
+ unsigned lld_busy:1; /* Exporting busy state for stacking
+ * drivers.
+ *
+ * 1 - There is one or more requests
+ * in the device's queue,
+ * and the device (or target/host)
+ * can not dispatch any request
+ * immediately.
+ * 0 - The device can dispatch
+ * (or kill) requests immediately,
+ * or there is no request in
+ * the device's queue even though
+ * target/host may busy. */
DECLARE_BITMAP(supported_events, SDEV_EVT_MAXBITS); /* supported events */
struct list_head event_list; /* asserted events */
--
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