1 files changed, 19 insertions, 25 deletions

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 2d63c8ad1442..6d5c7ff43f5b 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -67,6 +67,13 @@ static struct scsi_host_sg_pool scsi_sg_pools[] = {
 
 struct kmem_cache *scsi_sdb_cache;
 
+/*
+ * When to reinvoke queueing after a resource shortage. It's 3 msecs to
+ * not change behaviour from the previous unplug mechanism, experimentation
+ * may prove this needs changing.
+ */
+#define SCSI_QUEUE_DELAY        3
+
 static void scsi_run_queue(struct request_queue *q);
 
 /*
@@ -149,14 +156,7 @@ static int __scsi_queue_insert(struct scsi_cmnd *cmd, int reason, int unbusy)
         /*
          * Requeue this command.  It will go before all other commands
          * that are already in the queue.
-         *
-         * NOTE: there is magic here about the way the queue is plugged if
-         * we have no outstanding commands.
-         * 
-         * Although we *don't* plug the queue, we call the request
-         * function.  The SCSI request function detects the blocked condition
-         * and plugs the queue appropriately.
-         */
+         */
         spin_lock_irqsave(q->queue_lock, flags);
         blk_requeue_request(q, cmd->request);
         spin_unlock_irqrestore(q->queue_lock, flags);
@@ -1226,11 +1226,11 @@ int scsi_prep_return(struct request_queue *q, struct request *req, int ret)
         case BLKPREP_DEFER:
                 /*
                  * If we defer, the blk_peek_request() returns NULL, but the
-                 * queue must be restarted, so we plug here if no returning
-                 * command will automatically do that.
+                 * queue must be restarted, so we schedule a callback to happen
+                 * shortly.
                  */
                 if (sdev->device_busy == 0)
-                        blk_plug_device(q);
+                        blk_delay_queue(q, SCSI_QUEUE_DELAY);
                 break;
         default:
                 req->cmd_flags |= REQ_DONTPREP;
@@ -1269,7 +1269,7 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
                                    sdev_printk(KERN_INFO, sdev,
                                    "unblocking device at zero depth\n"));
                 } else {
-                        blk_plug_device(q);
+                        blk_delay_queue(q, SCSI_QUEUE_DELAY);
                         return 0;
                 }
         }
@@ -1499,7 +1499,7 @@ static void scsi_request_fn(struct request_queue *q)
          * the host is no longer able to accept any more requests.
          */
         shost = sdev->host;
-        while (!blk_queue_plugged(q)) {
+        for (;;) {
                 int rtn;
                 /*
                  * get next queueable request.  We do this early to make sure
@@ -1578,15 +1578,8 @@ static void scsi_request_fn(struct request_queue *q)
                  */
                 rtn = scsi_dispatch_cmd(cmd);
                 spin_lock_irq(q->queue_lock);
-                if(rtn) {
-                        /* we're refusing the command; because of
-                         * the way locks get dropped, we need to 
-                         * check here if plugging is required */
-                        if(sdev->device_busy == 0)
-                                blk_plug_device(q);
-
-                        break;
-                }
+                if (rtn)
+                        goto out_delay;
         }
 
         goto out;
@@ -1605,9 +1598,10 @@ static void scsi_request_fn(struct request_queue *q)
         spin_lock_irq(q->queue_lock);
         blk_requeue_request(q, req);
         sdev->device_busy--;
-        if(sdev->device_busy == 0)
-                blk_plug_device(q);
- out:
+out_delay:
+        if (sdev->device_busy == 0)
+                blk_delay_queue(q, SCSI_QUEUE_DELAY);
+out:
         /* must be careful here...if we trigger the ->remove() function
          * we cannot be holding the q lock */
         spin_unlock_irq(q->queue_lock);