syzkaller found the following splat with CONFIG_DEBUG_KOBJECT_RELEASE=y:

  Read of size 1 at addr ffff000028e896b8 by task kworker/1:2/228

  CPU: 1 PID: 228 Comm: kworker/1:2 Tainted: G S                5.9.0-rc8+ #101
  Hardware name: linux,dummy-virt (DT)
  Workqueue: events kobject_delayed_cleanup
  Call trace:
   dump_backtrace+0x0/0x4d8
   show_stack+0x34/0x48
   dump_stack+0x174/0x1f8
   print_address_description.constprop.0+0x5c/0x550
   kasan_report+0x13c/0x1c0
   __asan_report_load1_noabort+0x34/0x60
   memcmp+0xd0/0xd8
   gfs2_uevent+0xc4/0x188
   kobject_uevent_env+0x54c/0x1240
   kobject_uevent+0x2c/0x40
   __kobject_del+0x190/0x1d8
   kobject_delayed_cleanup+0x2bc/0x3b8
   process_one_work+0x96c/0x18c0
   worker_thread+0x3f0/0xc30
   kthread+0x390/0x498
   ret_from_fork+0x10/0x18

  Allocated by task 1110:
   kasan_save_stack+0x28/0x58
   __kasan_kmalloc.isra.0+0xc8/0xe8
   kasan_kmalloc+0x10/0x20
   kmem_cache_alloc_trace+0x1d8/0x2f0
   alloc_super+0x64/0x8c0
   sget_fc+0x110/0x620
   get_tree_bdev+0x190/0x648
   gfs2_get_tree+0x50/0x228
   vfs_get_tree+0x84/0x2e8
   path_mount+0x1134/0x1da8
   do_mount+0x124/0x138
   __arm64_sys_mount+0x164/0x238
   el0_svc_common.constprop.0+0x15c/0x598
   do_el0_svc+0x60/0x150
   el0_svc+0x34/0xb0
   el0_sync_handler+0xc8/0x5b4
   el0_sync+0x15c/0x180

  Freed by task 228:
   kasan_save_stack+0x28/0x58
   kasan_set_track+0x28/0x40
   kasan_set_free_info+0x24/0x48
   __kasan_slab_free+0x118/0x190
   kasan_slab_free+0x14/0x20
   slab_free_freelist_hook+0x6c/0x210
   kfree+0x13c/0x460

Use the same pattern as f2fs + ext4 where the kobject destruction must
complete before allowing the FS itself to be freed.  This means that we
need an explicit free_sbd in the callers.

Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Signed-off-by: Jamie Iles <jamie@nuviainc.com>
[Also go to fail_free when init_names fails.]
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>