Revert "block: recursive merge requests"

This reverts commit 27419322.

We have some problems related to selection of empty queues
that need to be resolved, evidence so far points to the
recursive merge logic making either being the cause or at
least the accelerator for this. So revert it for now, until
we figure this out.
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/elevator.c

@@ -515,7 +515,6 @@ static bool elv_attempt_insert_merge(struct request_queue *q,
 				     struct request *rq)
 {
 	struct request *__rq;
-	bool ret;
 
 	if (blk_queue_nomerges(q))
 		return false;
@@ -529,21 +528,14 @@ static bool elv_attempt_insert_merge(struct request_queue *q,
 	if (blk_queue_noxmerges(q))
 		return false;
 
-	ret = false;
 	/*
 	 * See if our hash lookup can find a potential backmerge.
 	 */
-	while (1) {
-		__rq = elv_rqhash_find(q, blk_rq_pos(rq));
-		if (!__rq || !blk_attempt_req_merge(q, __rq, rq))
-			break;
-
-		/* The merged request could be merged with others, try again */
-		ret = true;
-		rq = __rq;
-	}
+	__rq = elv_rqhash_find(q, blk_rq_pos(rq));
+	if (__rq && blk_attempt_req_merge(q, __rq, rq))
+		return true;
 
-	return ret;
+	return false;
 }
 
 void elv_merged_request(struct request_queue *q, struct request *rq, int type)