FAILED: patch "[PATCH] dm: fix potential for q->make_request_fn NULL pointer" failed to apply to 4.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 47ace7e012b9f7ad71d43ac9063d335ea3d6820b Mon Sep 17 00:00:00 2001
From: Mike Snitzer <snitzer@redhat.com>
Date: Mon, 27 Jan 2020 14:07:23 -0500
Subject: [PATCH] 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 e8f9661a10a1..b89f07ee2eff 100644
--- 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);