dm: fix incomplete request_queue initialization

DM is no longer prone to having its request_queue be improperly
initialized.

Summary of changes:

- defer DM's blk_register_queue() from add_disk()-time until
  dm_setup_md_queue() by using add_disk_no_queue_reg() in alloc_dev().

- dm_setup_md_queue() is updated to fully initialize DM's request_queue
  (_after_ all table loads have occurred and the request_queue's type,
  features and limits are known).

A very welcome side-effect of these changes is DM no longer needs to:
1) backfill the "mq" sysfs entry (because historically DM didn't
initialize the request_queue to use blk-mq until _after_
blk_register_queue() was called via add_disk()).
2) call elv_register_queue() to get .request_fn request-based DM
device's "iosched" exposed in syfs.

In addition, blk-mq debugfs support is now made available because
request-based DM's blk-mq request_queue is now properly initialized
before dm_setup_md_queue() calls blk_register_queue().

These changes also stave off the need to introduce new DM-specific
workarounds in block core, e.g. this proposal:
https://patchwork.kernel.org/patch/10067961/

In the end DM devices should be less unicorn in nature (relative to
initialization and availability of block core infrastructure provided by
the request_queue).

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Tested-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/md/dm-rq.c b/drivers/md/dm-rq.c
index 9d32f25..c28357f 100644 (file)
--- a/drivers/md/dm-rq.c
+++ b/drivers/md/dm-rq.c
@@ -713,8 +713,6 @@ int dm_old_init_request_queue(struct mapped_device *md, struct dm_table *t)
                return error;
        }
 
-       elv_register_queue(md->queue);
-
        return 0;
 }
 
@@ -812,15 +810,8 @@ int dm_mq_init_request_queue(struct mapped_device *md, struct dm_table *t)
        }
        dm_init_md_queue(md);
 
-       /* backfill 'mq' sysfs registration normally done in blk_register_queue */
-       err = blk_mq_register_dev(disk_to_dev(md->disk), q);
-       if (err)
-               goto out_cleanup_queue;
-
        return 0;
 
-out_cleanup_queue:
-       blk_cleanup_queue(q);
 out_tag_set:
        blk_mq_free_tag_set(md->tag_set);
 out_kfree_tag_set:

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 7475739..8c26bfc 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1761,7 +1761,7 @@ static struct mapped_device *alloc_dev(int minor)
                goto bad;
        md->dax_dev = dax_dev;
 
-       add_disk(md->disk);
+       add_disk_no_queue_reg(md->disk);
        format_dev_t(md->name, MKDEV(_major, minor));
 
        md->wq = alloc_workqueue("kdmflush", WQ_MEM_RECLAIM, 0);
@@ -2021,6 +2021,7 @@ EXPORT_SYMBOL_GPL(dm_get_queue_limits);
 int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 {
        int r;
+       struct queue_limits limits;
        enum dm_queue_mode type = dm_get_md_type(md);
 
        switch (type) {
@@ -2057,6 +2058,14 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
                break;
        }
 
+       r = dm_calculate_queue_limits(t, &limits);
+       if (r) {
+               DMERR("Cannot calculate initial queue limits");
+               return r;
+       }
+       dm_table_set_restrictions(t, md->queue, &limits);
+       blk_register_queue(md->disk);
+
        return 0;
 }