[PATCH] blk: fix merge bug in as-iosched

as-iosched deals with aliased requests differently from other ioscheds.

It links together aliased requests using rq->queuelist instead of
spilling alises to dispatch queue like other ioscheds do.  Requests
linked in this way cannot be merged.

Unfortunately, generic q->last_merge handling patch didn't take this
into account and q->last_merge could be set to an aliased request
resulting in Badness, corrupt list and eventually panic.

This explicitly marks aliased requests to be unmergeable.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/as-iosched.c

@@ -1344,6 +1344,7 @@ as_add_aliased_request(struct as_data *ad, struct as_rq *arq, struct as_rq *alia
 	 * Don't want to have to handle merges.
 	 */
 	as_del_arq_hash(arq);
+	arq->request->flags |= REQ_NOMERGE;
 }
 
 /*