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Subject[PATCH 4.14 169/173] dm: fix potential for q->make_request_fn NULL pointer
Date
From: Mike Snitzer <snitzer@redhat.com>

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]
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1647,7 +1647,6 @@ void dm_init_md_queue(struct mapped_devi
* - must do so here (in alloc_dev callchain) before queue is used
*/
md->queue->queuedata = md;
- md->queue->backing_dev_info->congested_data = md;
}

void dm_init_normal_md_queue(struct mapped_device *md)
@@ -1658,6 +1657,7 @@ void dm_init_normal_md_queue(struct mapp
/*
* 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;
}

@@ -1750,6 +1750,12 @@ static struct mapped_device *alloc_dev(i
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_node(1, numa_node_id);
if (!md->disk)
@@ -2055,7 +2061,6 @@ 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);
/*
* 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).

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