dm: fix request-based DM to not bounce through indirect dm_submit_bio

It is unnecessary to force request-based DM to call into bio-based
dm_submit_bio (via indirect disk->fops->submit_bio) only to have it then
call blk_mq_submit_bio().

Fix this by establishing a request-based DM block_device_operations
(dm_rq_blk_dops, which doesn't have .submit_bio) and update
dm_setup_md_queue() to set md->disk->fops to it for
DM_TYPE_REQUEST_BASED.

Remove DM_TYPE_REQUEST_BASED conditional in dm_submit_bio and unexport
blk_mq_submit_bio.

Fixes: c62b37d96b6eb ("block: move ->make_request_fn to struct block_device_operations")
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 176698b..0191fc0 100644 (file)
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -2265,7 +2265,6 @@ queue_exit:
        blk_queue_exit(q);
        return BLK_QC_T_NONE;
 }
-EXPORT_SYMBOL_GPL(blk_mq_submit_bio); /* only for request based dm */
 
 void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
                     unsigned int hctx_idx)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index af1bab3..e396ec2 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1633,18 +1633,6 @@ static blk_qc_t dm_submit_bio(struct bio *bio)
        int srcu_idx;
        struct dm_table *map;
 
-       if (dm_get_md_type(md) == DM_TYPE_REQUEST_BASED) {
-               /*
-                * We are called with a live reference on q_usage_counter, but
-                * that one will be released as soon as we return.  Grab an
-                * extra one as blk_mq_submit_bio expects to be able to consume
-                * a reference (which lives until the request is freed in case a
-                * request is allocated).
-                */
-               percpu_ref_get(&bio->bi_disk->queue->q_usage_counter);
-               return blk_mq_submit_bio(bio);
-       }
-
        map = dm_get_live_table(md, &srcu_idx);
        if (unlikely(!map)) {
                DMERR_LIMIT("%s: mapping table unavailable, erroring io",
@@ -1727,6 +1715,7 @@ static int next_free_minor(int *minor)
 }
 
 static const struct block_device_operations dm_blk_dops;
+static const struct block_device_operations dm_rq_blk_dops;
 static const struct dax_operations dm_dax_ops;
 
 static void dm_wq_work(struct work_struct *work);
@@ -2113,9 +2102,10 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 
        switch (type) {
        case DM_TYPE_REQUEST_BASED:
+               md->disk->fops = &dm_rq_blk_dops;
                r = dm_mq_init_request_queue(md, t);
                if (r) {
-                       DMERR("Cannot initialize queue for request-based dm-mq mapped device");
+                       DMERR("Cannot initialize queue for request-based dm mapped device");
                        return r;
                }
                break;
@@ -3095,6 +3085,15 @@ static const struct block_device_operations dm_blk_dops = {
        .owner = THIS_MODULE
 };
 
+static const struct block_device_operations dm_rq_blk_dops = {
+       .open = dm_blk_open,
+       .release = dm_blk_close,
+       .ioctl = dm_blk_ioctl,
+       .getgeo = dm_blk_getgeo,
+       .pr_ops = &dm_pr_ops,
+       .owner = THIS_MODULE
+};
+
 static const struct dax_operations dm_dax_ops = {
        .direct_access = dm_dax_direct_access,
        .dax_supported = dm_dax_supported,