block: Make del_gendisk() safer for disks without queues

BugLink: http://bugs.launchpad.net/bugs/1659111
Commit 165a5e22fafb "block: Move bdi_unregister() to del_gendisk()"
added disk->queue dereference to del_gendisk(). Although del_gendisk()
is not supposed to be called without disk->queue valid and
blk_unregister_queue() warns in that case, this change will make it oops
instead. Return to the old more robust behavior of just warning when
del_gendisk() gets called for gendisk with disk->queue being NULL.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Tested-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit 90f16fddcc2802726142b8386c65ccb89f044613)
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Brad Figg <brad.figg@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/block/genhd.c b/block/genhd.c
index 6a6c7f544100c6f933a3edb4bf32d52d6e83657d..94650782079867257c7fb09028b24ea594d3ff28 100644 (file)
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -658,12 +658,16 @@ void del_gendisk(struct gendisk *disk)
        disk->flags &= ~GENHD_FL_UP;
 
        sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
-       /*
-        * Unregister bdi before releasing device numbers (as they can get
-        * reused and we'd get clashes in sysfs).
-        */
-       bdi_unregister(disk->queue->backing_dev_info);
-       blk_unregister_queue(disk);
+       if (disk->queue) {
+               /*
+                * Unregister bdi before releasing device numbers (as they can
+                * get reused and we'd get clashes in sysfs).
+                */
+               bdi_unregister(disk->queue->backing_dev_info);
+               blk_unregister_queue(disk);
+       } else {
+               WARN_ON(1);
+       }
        blk_unregister_region(disk_devt(disk), disk->minors);
 
        part_stat_set_all(&disk->part0, 0);