block: split request allocation components into helpers

This is in preparation for a fix, but serves as a cleanup as well moving
the cached vs regular alloc logic out of blk_mq_submit_bio().

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

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 5498454..dcb4132 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2478,6 +2478,51 @@ static inline unsigned short blk_plug_max_rq_count(struct blk_plug *plug)
        return BLK_MAX_REQUEST_COUNT;
 }
 
+static struct request *blk_mq_get_new_requests(struct request_queue *q,
+                                              struct blk_plug *plug,
+                                              struct bio *bio)
+{
+       struct blk_mq_alloc_data data = {
+               .q              = q,
+               .nr_tags        = 1,
+               .cmd_flags      = bio->bi_opf,
+       };
+       struct request *rq;
+
+       if (plug) {
+               data.nr_tags = plug->nr_ios;
+               plug->nr_ios = 1;
+               data.cached_rq = &plug->cached_rq;
+       }
+
+       rq = __blk_mq_alloc_requests(&data);
+       if (rq)
+               return rq;
+
+       rq_qos_cleanup(q, bio);
+       if (bio->bi_opf & REQ_NOWAIT)
+               bio_wouldblock_error(bio);
+       return NULL;
+}
+
+static inline struct request *blk_mq_get_request(struct request_queue *q,
+                                                struct blk_plug *plug,
+                                                struct bio *bio)
+{
+       if (plug) {
+               struct request *rq;
+
+               rq = rq_list_peek(&plug->cached_rq);
+               if (rq) {
+                       plug->cached_rq = rq_list_next(rq);
+                       INIT_LIST_HEAD(&rq->queuelist);
+                       return rq;
+               }
+       }
+
+       return blk_mq_get_new_requests(q, plug, bio);
+}
+
 /**
  * blk_mq_submit_bio - Create and send a request to block device.
  * @bio: Bio pointer.
@@ -2518,29 +2563,9 @@ void blk_mq_submit_bio(struct bio *bio)
        rq_qos_throttle(q, bio);
 
        plug = blk_mq_plug(q, bio);
-       if (plug && plug->cached_rq) {
-               rq = rq_list_pop(&plug->cached_rq);
-               INIT_LIST_HEAD(&rq->queuelist);
-       } else {
-               struct blk_mq_alloc_data data = {
-                       .q              = q,
-                       .nr_tags        = 1,
-                       .cmd_flags      = bio->bi_opf,
-               };
-
-               if (plug) {
-                       data.nr_tags = plug->nr_ios;
-                       plug->nr_ios = 1;
-                       data.cached_rq = &plug->cached_rq;
-               }
-               rq = __blk_mq_alloc_requests(&data);
-               if (unlikely(!rq)) {
-                       rq_qos_cleanup(q, bio);
-                       if (bio->bi_opf & REQ_NOWAIT)
-                               bio_wouldblock_error(bio);
-                       goto queue_exit;
-               }
-       }
+       rq = blk_mq_get_request(q, plug, bio);
+       if (unlikely(!rq))
+               goto queue_exit;
 
        trace_block_getrq(bio);