block: bypass ->make_request_fn for blk-mq drivers
Call blk_mq_make_request when no ->make_request_fn is set. This is
safe now that blk_alloc_queue always sets up the pointer for make_request
based drivers. This avoids an indirect call in the blk-mq driver I/O
fast path, which is rather expensive due to spectre mitigations.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index db9e461..0eb93da 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1788,6 +1788,9 @@ static blk_qc_t dm_make_request(struct request_queue *q, struct bio *bio)
int srcu_idx;
struct dm_table *map;
+ if (dm_get_md_type(md) == DM_TYPE_REQUEST_BASED)
+ return blk_mq_make_request(q, bio);
+
map = dm_get_live_table(md, &srcu_idx);
/* if we're suspended, we have to queue this io for later */