block: don't protect generic_make_request_checks with blk_queue_enter

Now a063057 ("block: Fix a race between request queue removal and
the block cgroup controller") has been reverted, and blkcg_exit_queue()
won't be called in blk_cleanup_queue() any more.

So don't need to protect generic_make_request_checks() with
blk_queue_enter(), then the total mess can be cleaned.

37f9579 ("blk-mq: Avoid that submitting a bio concurrently with device
removal triggers a crash") is reverted.

Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-core.c

@@ -957,22 +957,8 @@ blk_qc_t generic_make_request(struct bio *bio)
 	 * yet.
 	 */
 	struct bio_list bio_list_on_stack[2];
-	blk_mq_req_flags_t flags = 0;
-	struct request_queue *q = bio->bi_disk->queue;
 	blk_qc_t ret = BLK_QC_T_NONE;
 
-	if (bio->bi_opf & REQ_NOWAIT)
-		flags = BLK_MQ_REQ_NOWAIT;
-	if (bio_flagged(bio, BIO_QUEUE_ENTERED))
-		blk_queue_enter_live(q);
-	else if (blk_queue_enter(q, flags) < 0) {
-		if (!blk_queue_dying(q) && (bio->bi_opf & REQ_NOWAIT))
-			bio_wouldblock_error(bio);
-		else
-			bio_io_error(bio);
-		return ret;
-	}
-
 	if (!generic_make_request_checks(bio))
 		goto out;
 
@@ -1009,29 +995,20 @@ blk_qc_t generic_make_request(struct bio *bio)
 	bio_list_init(&bio_list_on_stack[0]);
 	current->bio_list = bio_list_on_stack;
 	do {
-		bool enter_succeeded = true;
-
-		if (unlikely(q != bio->bi_disk->queue)) {
-			if (q)
-				blk_queue_exit(q);
-			q = bio->bi_disk->queue;
-			flags = 0;
-			if (bio->bi_opf & REQ_NOWAIT)
-				flags = BLK_MQ_REQ_NOWAIT;
-			if (blk_queue_enter(q, flags) < 0) {
-				enter_succeeded = false;
-				q = NULL;
-			}
-		}
+		struct request_queue *q = bio->bi_disk->queue;
+		blk_mq_req_flags_t flags = bio->bi_opf & REQ_NOWAIT ?
+			BLK_MQ_REQ_NOWAIT : 0;
 
-		if (enter_succeeded) {
+		if (likely(blk_queue_enter(q, flags) == 0)) {
 			struct bio_list lower, same;
 
 			/* Create a fresh bio_list for all subordinate requests */
 			bio_list_on_stack[1] = bio_list_on_stack[0];
 			bio_list_init(&bio_list_on_stack[0]);
 			ret = q->make_request_fn(q, bio);
 
+			blk_queue_exit(q);
+
 			/* sort new bios into those for a lower level
 			 * and those for the same level
 			 */
@@ -1058,8 +1035,6 @@ blk_qc_t generic_make_request(struct bio *bio)
 	current->bio_list = NULL; /* deactivate */
 
 out:
-	if (q)
-		blk_queue_exit(q);
 	return ret;
 }
 EXPORT_SYMBOL(generic_make_request);