The patch below does not apply to the 4.9-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);