[PATCH] fix scsi oops on failed sg table allocation

This patch fixes the deliberate BUG_ON() on failed sgtable allocations.
I left that in because I was too lazy to fix it at the time...

Basically make scsi_init_io() return 0 on failure (like before) but this
time allow us to recover. scsi_init_io() will end_request on a fatal
condition. So now just mark the device/host as starved if needed, and
leave the request at the front of the queue for next service.

drivers/scsi/scsi_lib.c

@@ -963,21 +963,22 @@ void scsi_request_fn(request_queue_t * q)
 
 			/* 
 			 * This sets up the scatter-gather table (allocating if
-			 * required).  Hosts that need bounce buffers will also
-			 * get those allocated here.  
+			 * required).
 			 */
 			if (!scsi_init_io(SCpnt)) {
-				SCpnt = __scsi_end_request(SCpnt, 0, 
-							   SCpnt->request.nr_sectors, 0, 0);
-				if( SCpnt != NULL )
-				{
-					panic("Should not have leftover blocks\n");
-				}
 				spin_lock_irq(q->queue_lock);
 				SHpnt->host_busy--;
 				SDpnt->device_busy--;
-				continue;
+				if (SDpnt->device_busy == 0) {
+					SDpnt->starved = 1;
+					SHpnt->some_device_starved = 1;
+				}
+				SCpnt->request.special = SCpnt;
+				SCpnt->request.flags |= REQ_SPECIAL;
+				_elv_add_request(q, &SCpnt->request, 0, 0);
+				break;
 			}
+
 			/*
 			 * Initialize the actual SCSI command for this request.
 			 */

drivers/scsi/scsi_merge.c

@@ -78,8 +78,12 @@ int scsi_init_io(Scsi_Cmnd *SCpnt)
 	if (in_interrupt())
 		gfp_mask &= ~__GFP_WAIT;
 
+	/*
+	 * if sg table allocation fails, requeue request later.
+	 */
 	sgpnt = scsi_alloc_sgtable(SCpnt, gfp_mask);
-	BUG_ON(!sgpnt);
+	if (!sgpnt)
+		return 0;
 
 	SCpnt->request_buffer = (char *) sgpnt;
 	SCpnt->request_bufflen = req->nr_sectors << 9;
@@ -102,8 +106,13 @@ int scsi_init_io(Scsi_Cmnd *SCpnt)
 	printk("Incorrect number of segments after building list\n");
 	printk("counted %d, received %d\n", count, SCpnt->use_sg);
 	printk("req nr_sec %lu, cur_nr_sec %u\n", req->nr_sectors, req->current_nr_sectors);
-	BUG();
-	return 0; /* ahem */
+
+	/*
+	 * kill it. there should be no leftover blocks in this request
+	 */
+	SCpnt = scsi_end_request(SCpnt, 0, req->nr_sectors);
+	BUG_ON(SCpnt);
+	return 0;
 }
 
 /*