[PATCH 4.16 35/64] nbd: fix nbd device deletion

[Greg Kroah-Hartman]

4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Josef Bacik <jba...@fb.com>

commit 8364da4751cf22201d74933d5e634176f44ed407 upstream.

This fixes a use after free bug, we shouldn't be doing disk->queue right
after we do del_gendisk(disk).  Save the queue and do the cleanup after
the del_gendisk.

Fixes: c6a4759ea0c9 ("nbd: add device refcounting")
cc: sta...@vger.kernel.org
Signed-off-by: Josef Bacik <jba...@fb.com>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/block/nbd.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -173,9 +173,12 @@ static const struct device_attribute pid
 static void nbd_dev_remove(struct nbd_device *nbd)
 {
        struct gendisk *disk = nbd->disk;
+       struct request_queue *q;
+
        if (disk) {
+               q = disk->queue;
                del_gendisk(disk);
-               blk_cleanup_queue(disk->queue);
+               blk_cleanup_queue(q);
                blk_mq_free_tag_set(&nbd->tag_set);
                disk->private_data = NULL;
                put_disk(disk);