[PATCH] AS oops fix

From: Nick Piggin <piggin@cyberone.com.au>

If a request is merged with another, it sometimes has to be repositioned on
the rbtree - you just do a delete then an add.  This is a quite uncommon
case though.

I changed the way adding works, so collisions must be handled by the caller
instead of being dumbly fixed by the add routine.  Unfortunately the
uncommon callers weren't handling it properly.

drivers/block/as-iosched.c

@@ -1303,7 +1303,7 @@ static struct request *as_next_request(request_queue_t *q)
  * Add arq to a list behind alias
  */
 static inline void
-as_add_aliased_request(struct as_rq *arq, struct as_rq *alias)
+as_add_aliased_request(struct as_data *ad, struct as_rq *arq, struct as_rq *alias)
 {
 	/*
 	 * Another request with the same start sector on the rbtree.
@@ -1312,6 +1312,11 @@ as_add_aliased_request(struct as_rq *arq, struct as_rq *alias)
 	 */
 	list_add_tail(&arq->request->queuelist,	&alias->request->queuelist);
 
+	/*
+	 * Don't want to have to handle merges.
+	 */
+	as_remove_merge_hints(ad->q, arq);
+
 }
 
 /*
@@ -1353,7 +1358,7 @@ static void as_add_request(struct as_data *ad, struct as_rq *arq)
 		as_update_arq(ad, arq); /* keep state machine up to date */
 
 	} else {
-		as_add_aliased_request(arq, alias);
+		as_add_aliased_request(ad, arq, alias);
 		/*
 		 * have we been anticipating this request?
 		 * or does it come from the same process as the one we are
@@ -1553,8 +1558,10 @@ static void as_merged_request(request_queue_t *q, struct request *req)
 		 * currently don't bother. Ditto the next function.
 		 */
 		as_del_arq_rb(ad, arq);
-		if ((alias = as_add_arq_rb(ad, arq)) )
-			as_add_aliased_request(arq, alias);
+		if ((alias = as_add_arq_rb(ad, arq)) ) {
+			list_del_init(&arq->fifo);
+			as_add_aliased_request(ad, arq, alias);
+		}
 		/*
 		 * Note! At this stage of this and the next function, our next
 		 * request may not be optimal - eg the request may have "grown"
@@ -1586,8 +1593,10 @@ as_merged_requests(request_queue_t *q, struct request *req,
 	if (rq_rb_key(req) != arq->rb_key) {
 		struct as_rq *alias;
 		as_del_arq_rb(ad, arq);
-		if ((alias = as_add_arq_rb(ad, arq)) )
-			as_add_aliased_request(arq, alias);
+		if ((alias = as_add_arq_rb(ad, arq)) ) {
+			list_del_init(&arq->fifo);
+			as_add_aliased_request(ad, arq, alias);
+		}
 	}
 
 	/*