Merge branch 'for-2.6.39/core' of git://git.kernel.dk/linux-2.6-block

* 'for-2.6.39/core' of git://git.kernel.dk/linux-2.6-block: (65 commits)
  Documentation/iostats.txt: bit-size reference etc.
  cfq-iosched: removing unnecessary think time checking
  cfq-iosched: Don't clear queue stats when preempt.
  blk-throttle: Reset group slice when limits are changed
  blk-cgroup: Only give unaccounted_time under debug
  cfq-iosched: Don't set active queue in preempt
  block: fix non-atomic access to genhd inflight structures
  block: attempt to merge with existing requests on plug flush
  block: NULL dereference on error path in __blkdev_get()
  cfq-iosched: Don't update group weights when on service tree
  fs: assign sb->s_bdi to default_backing_dev_info if the bdi is going away
  block: Require subsystems to explicitly allocate bio_set integrity mempool
  jbd2: finish conversion from WRITE_SYNC_PLUG to WRITE_SYNC and explicit plugging
  jbd: finish conversion from WRITE_SYNC_PLUG to WRITE_SYNC and explicit plugging
  fs: make fsync_buffers_list() plug
  mm: make generic_writepages() use plugging
  blk-cgroup: Add unaccounted time to timeslice_used.
  block: fixup plugging stubs for !CONFIG_BLOCK
  block: remove obsolete comments for blkdev_issue_zeroout.
  blktrace: Use rq->cmd_flags directly in blk_add_trace_rq.
  ...

Fix up conflicts in fs/{aio.c,super.c}

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);