dm: fix potential for q->make_request_fn NULL pointer

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@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>
[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>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index c752c55..c4d4cd3 100644 (file)
--- a/drivers/md/dm.c
+++ b/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).