[BUG] fs: dlm: possible ABBA deadlock

[Jia-Ju Bai]

Hello,

My static analysis tool reports a possible ABBA deadlock in the dlm 
filesystem in Linux 5.10:

dlm_recover_waiters_pre()
  mutex_lock(&ls->ls_waiters_mutex); --> line 5130
  recover_convert_waiter()
    _receive_convert_reply()
      lock_rsb()
        mutex_lock(&r->res_mutex); --> line 69

dlm_recover_waiters_post()
  lock_rsb()
    mutex_lock(&r->res_mutex); --> line 69
  mutex_lock(&ls->ls_waiters_mutex); --> line 5307

When dlm_recover_waiters_pre() and dlm_recover_waiters_post() are 
concurrently executed, the deadlock can occur.

I am not quite sure whether this possible deadlock is real and how to 
fix it if it is real.
Any feedback would be appreciated, thanks :)

Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>


Best wishes,
Jia-Ju Bai