dm: fix potential for q->make_request_fn NULL pointer

BugLink: https://bugs.launchpad.net/bugs/1864775

commit 47ace7e0 upstream.

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: ff36ab34 ("dm: remove request-based logic from make_request_fn wrapper")
Depends-on: c12c9a3c ("dm: various cleanups to md->queue initialization code")
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
[smb: adjusted for context and dm_init_md_queue() exitsting in older
      kernels, and congested_data embedded in backing_dev_info, and
      dm_init_normal_md_queue() was called dm_init_old_md_queue()]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

drivers/md/dm.c

@@ -2293,7 +2293,6 @@ static void dm_init_md_queue(struct mapped_device *md)
 	 * - must do so here (in alloc_dev callchain) before queue is used
 	 */
 	md->queue->queuedata = md;
-	md->queue->backing_dev_info->congested_data = md;
 }
 
 static void dm_init_old_md_queue(struct mapped_device *md)
@@ -2304,6 +2303,7 @@ static void dm_init_old_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;
 	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
 }
@@ -2386,6 +2386,12 @@ static struct mapped_device *alloc_dev(int minor)
 		goto bad;
 
 	dm_init_md_queue(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(1);
 	if (!md->disk)
@@ -2849,7 +2855,6 @@ int dm_setup_md_queue(struct mapped_device *md)
 		break;
 	case DM_TYPE_BIO_BASED:
 		dm_init_old_md_queue(md);
-		blk_queue_make_request(md->queue, dm_make_request);
 		/*
 		 * DM handles splitting bios as needed.  Free the bio_split bioset
 		 * since it won't be used (saves 1 process per bio-based DM device).