dm: fix potential for q->make_request_fn NULL pointer

Move blk_queue_make_request() to dm.c:alloc_dev() so that
q->make_request_fn is never NULL during the lifetime of a DM device
(even one that is created without a DM table).

Otherwise generic_make_request() will crash simply by doing:
  dmsetup create -n test
  mount /dev/dm-N /mnt

While at it, move ->congested_data initialization out of
dm.c:alloc_dev() and into the bio-based specific init method.

Reported-by: Stefan Bader <stefan.bader@canonical.com>
BugLink: https://bugs.launchpad.net/bugs/1860231
Fixes: ff36ab34583a ("dm: remove request-based logic from make_request_fn wrapper")
Depends-on: c12c9a3c3860c ("dm: various cleanups to md->queue initialization code")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index e8f9661..b89f07e 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1859,6 +1859,7 @@ static void dm_init_normal_md_queue(struct mapped_device *md)
        /*
         * Initialize aspects of queue that aren't relevant for blk-mq
         */
+       md->queue->backing_dev_info->congested_data = md;
        md->queue->backing_dev_info->congested_fn = dm_any_congested;
 }
 
@@ -1949,7 +1950,12 @@ static struct mapped_device *alloc_dev(int minor)
        if (!md->queue)
                goto bad;
        md->queue->queuedata = md;
-       md->queue->backing_dev_info->congested_data = md;
+       /*
+        * default to bio-based required ->make_request_fn until DM
+        * table is loaded and md->type established. If request-based
+        * table is loaded: blk-mq will override accordingly.
+        */
+       blk_queue_make_request(md->queue, dm_make_request);
 
        md->disk = alloc_disk_node(1, md->numa_node_id);
        if (!md->disk)
@@ -2264,7 +2270,6 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
        case DM_TYPE_DAX_BIO_BASED:
        case DM_TYPE_NVME_BIO_BASED:
                dm_init_normal_md_queue(md);
-               blk_queue_make_request(md->queue, dm_make_request);
                break;
        case DM_TYPE_NONE:
                WARN_ON_ONCE(true);