scsi: Avoid crashing if device uses DIX but adapter does not support it

commit 91724c20 upstream.

This can happen if a multipathed device uses DIX and another path is
added via an adapter that does not support it.  Multipath should not
allow this path to be added, but we should not depend upon that to avoid
crashing.
Signed-off-by: Ewan D. Milne <emilne@redhat.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

drivers/scsi/scsi_lib.c

@@ -1096,7 +1096,17 @@ int scsi_init_io(struct scsi_cmnd *cmd, gfp_t gfp_mask)
 		struct scsi_data_buffer *prot_sdb = cmd->prot_sdb;
 		int ivecs, count;
 
-		BUG_ON(prot_sdb == NULL);
+		if (prot_sdb == NULL) {
+			/*
+			 * This can happen if someone (e.g. multipath)
+			 * queues a command to a device on an adapter
+			 * that does not support DIX.
+			 */
+			WARN_ON_ONCE(1);
+			error = BLKPREP_KILL;
+			goto err_exit;
+		}
+
 		ivecs = blk_rq_count_integrity_sg(rq->q, rq->bio);
 
 		if (scsi_alloc_sgtable(prot_sdb, ivecs, gfp_mask)) {