[SCSI] BUG_ON() impossible condition in sg list counting

If blk_rq_map_sg wrote more than was allocated in the scatterlist,
BUG_ON() is probably the right thing to do.

[jejb: rejections fixed up]

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index b0c59ae..aa17e71 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1104,7 +1104,6 @@
  *
  * Returns:     0 on success
  *		BLKPREP_DEFER if the failure is retryable
- *		BLKPREP_KILL if the failure is fatal
  */
 static int scsi_init_io(struct scsi_cmnd *cmd)
 {
@@ -1138,17 +1137,9 @@
 	 * each segment.
 	 */
 	count = blk_rq_map_sg(req->q, req, cmd->request_buffer);
-	if (likely(count <= cmd->use_sg)) {
-		cmd->use_sg = count;
-		return BLKPREP_OK;
-	}
-
-	printk(KERN_ERR "Incorrect number of segments after building list\n");
-	printk(KERN_ERR "counted %d, received %d\n", count, cmd->use_sg);
-	printk(KERN_ERR "req nr_sec %lu, cur_nr_sec %u\n", req->nr_sectors,
-			req->current_nr_sectors);
-
-	return BLKPREP_KILL;
+	BUG_ON(count > cmd->use_sg);
+	cmd->use_sg = count;
+	return BLKPREP_OK;
 }
 
 static struct scsi_cmnd *scsi_get_cmd_from_req(struct scsi_device *sdev,