ocfs2: keep locking_state within the cluster connection lifetime

The locking_state reader calls ocfs2_dlm_lvb() through the selected
cluster stack.  Its debug-object reference keeps the tracking list alive,
but does not keep that stack selected without a cluster connection.

DLM initialization publishes the file before establishing its connection,
and DLM shutdown drops the connection while the file still exists.  Both
the mount error unwind in ocfs2_mount_volume() and ocfs2_dismount_volume()
remove the debugfs subtree only after ocfs2_dlm_shutdown() has returned. 
Whenever the disconnect releases the last stack reference, which is the
case for a failed mount and for any unmount without a pending hangup, a
concurrent reader dereferences a NULL active_stack:

  Mount error unwind                  Debugfs reader
  ------------------                  --------------
  ocfs2_mount_volume(): out_dlm
    ocfs2_dlm_shutdown()
      disconnect last cluster
        clear active_stack
                                      read locking_state
                                        ocfs2_dlm_seq_show()
                                          ocfs2_dlm_lvb()
                                            dereference active_stack
  fill_super(): out_debugfs
    remove debugfs subtree

Publish the debug files only after the connection and the mount lock
resources are initialized, so a failed DLM initialization has no debug
reference to drop.  Remove them again in the common DLM shutdown helper
before the connection is dropped: debugfs removal waits for readers that
are inside the file operations, and the parent directory is still present
at that point in every caller.  This covers the mount error unwind, the
ocfs2_fill_super() failures after a successful mount that dismount with
mnt_err set, and unmounts whose disconnect releases the stack directly.

Only the relevant frames of the report are kept:

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000001: 0000 [#1] SMP KASAN NOPTI
KASAN: null-ptr-deref in range [0x0000000000000008-0x000000000000000f]
RIP: 0010:ocfs2_dlm_lvb+0x38/0xf0
Call Trace:
 <TASK>
 ocfs2_dlm_seq_show+0x36a/0xb70
 seq_read_iter+0x480/0x1110
 seq_read+0x362/0x5a0
 full_proxy_read+0x11f/0x180
 vfs_read+0x1a0/0xc20
 ksys_read+0x111/0x200
 </TASK>

Link: https://lore.kernel.org/pm-ocfs2-objects-candidate-0011-v7-61e3ef8b1ad44ac2e817@gmail.com
Fixes: 286eaa95c5c5 ("ocfs2: Break out stackglue into modules.")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Assisted-by: LLM
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: Jia-Ju Bai <baijiaju1990@gmail.com>
Cc: <jjzuming@gmail.com>
Cc: <stable@vger.kernel.org>

0 files changed, 0 insertions, 0 deletions