[PATCH 4.19 089/195] dm: fix potential for q->make_request_fn NULL pointer

[Greg Kroah-Hartman]

From: Mike Snitzer <snitzer@xxxxxxxxxx>

commit 47ace7e012b9f7ad71d43ac9063d335ea3d6820b 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@xxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/md/dm.c |    9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1819,6 +1819,7 @@ static void dm_init_normal_md_queue(stru
 	/*
 	 * 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;
 }
 
@@ -1913,7 +1914,12 @@ static struct mapped_device *alloc_dev(i
 	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)
@@ -2242,7 +2248,6 @@ int dm_setup_md_queue(struct mapped_devi
 	case DM_TYPE_BIO_BASED:
 	case DM_TYPE_DAX_BIO_BASED:
 		dm_init_normal_md_queue(md);
-		blk_queue_make_request(md->queue, dm_make_request);
 		break;
 	case DM_TYPE_NVME_BIO_BASED:
 		dm_init_normal_md_queue(md);