blk-mq: allow blk_mq_make_request to consume the q_usage_counter reference

blk_mq_make_request currently needs to grab an q_usage_counter
reference when allocating a request.  This is because the block layer
grabs one before calling blk_mq_make_request, but also releases it as
soon as blk_mq_make_request returns.  Remove the blk_queue_exit call
after blk_mq_make_request returns, and instead let it consume the
reference.  This works perfectly fine for the block layer caller, just
device mapper needs an extra reference as the old problem still
persists there.  Open code blk_queue_enter_live in device mapper,
as there should be no other callers and this allows better documenting
why we do a non-try get.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 20 insertions, 13 deletions

diff --git a/block/blk-core.c b/block/blk-core.c
index 1e97f9973523..78683ea61c93 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1066,6 +1066,20 @@ end_io:
 	return false;
 }
 
+static blk_qc_t do_make_request(struct bio *bio)
+{
+	struct request_queue *q = bio->bi_disk->queue;
+	blk_qc_t ret = BLK_QC_T_NONE;
+
+	if (blk_crypto_bio_prep(&bio)) {
+		if (!q->make_request_fn)
+			return blk_mq_make_request(q, bio);
+		ret = q->make_request_fn(q, bio);
+	}
+	blk_queue_exit(q);
+	return ret;
+}
+
 /**
  * generic_make_request - re-submit a bio to the block device layer for I/O
  * @bio:  The bio describing the location in memory and on the device.
@@ -1131,14 +1145,7 @@ blk_qc_t generic_make_request(struct bio *bio)
 			/* 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]);
-			if (blk_crypto_bio_prep(&bio)) {
-				if (q->make_request_fn)
-					ret = q->make_request_fn(q, bio);
-				else
-					ret = blk_mq_make_request(q, bio);
-			}
-
-			blk_queue_exit(q);
+			ret = do_make_request(bio);
 
 			/* sort new bios into those for a lower level
 			 * and those for the same level
@@ -1175,7 +1182,6 @@ EXPORT_SYMBOL(generic_make_request);
 blk_qc_t direct_make_request(struct bio *bio)
 {
 	struct request_queue *q = bio->bi_disk->queue;
-	blk_qc_t ret = BLK_QC_T_NONE;
 
 	if (WARN_ON_ONCE(q->make_request_fn)) {
 		bio_io_error(bio);
@@ -1185,10 +1191,11 @@ blk_qc_t direct_make_request(struct bio *bio)
 		return BLK_QC_T_NONE;
 	if (unlikely(bio_queue_enter(bio)))
 		return BLK_QC_T_NONE;
-	if (blk_crypto_bio_prep(&bio))
-		ret = blk_mq_make_request(q, bio);
-	blk_queue_exit(q);
-	return ret;
+	if (!blk_crypto_bio_prep(&bio)) {
+		blk_queue_exit(q);
+		return BLK_QC_T_NONE;
+	}
+	return blk_mq_make_request(q, bio);
 }
 EXPORT_SYMBOL_GPL(direct_make_request);