[BUG] block: drbd: four possible ABBA deadlocks

[Jia-Ju Bai]

Hello,

My static analysis tool reports four possible ABBA deadlocks in the drbd 
drivers in Linux 5.10:

### Deadlock A ###
w_after_conn_state_ch()
  mutex_lock(&connection->resource->conf_update); --> line 2065
  conn_free_crypto()
    drbd_free_sock()
      drbd_free_one_sock(&connection->data)
        mutex_lock(&ds->mutex); --> line 2967

drbd_adm_net_opts()
  mutex_lock(&connection->data.mutex); --> line 2445
  mutex_lock(&connection->resource->conf_update); --> line 2446

When w_after_conn_state_ch() and drbd_adm_net_opts() are concurrently 
executed, the deadlock can occur.

### Deadlock B ###
drbd_adm_connect()
  mutex_lock(&adm_ctx.resource->conf_update); --> line 2644
  conn_free_crypto()
    drbd_free_one_sock(&connection->data)
      mutex_lock(&ds->mutex); --> line 2967

drbd_adm_net_opts()
  mutex_lock(&connection->data.mutex); --> line 2445
  mutex_lock(&connection->resource->conf_update); --> line 2446

When drbd_adm_connect() and drbd_adm_net_opts() are concurrently 
executed, the deadlock can occur.

### Deadlock C ###
w_after_conn_state_ch()
  mutex_lock(&connection->resource->conf_update); --> line 2065
  conn_free_crypto()
    drbd_free_sock()
      drbd_free_one_sock(&connection->data)
        mutex_lock(&ds->mutex); --> line 2967

receive_protocol()
  mutex_lock(&connection->data.mutex); --> line 3778
  mutex_lock(&connection->resource->conf_update); --> line 3779

When w_after_conn_state_ch() and receive_protocol() are concurrently 
executed, the deadlock can occur.

### Deadlock D ###
drbd_adm_connect()
  mutex_lock(&adm_ctx.resource->conf_update); --> line 2644
  conn_free_crypto()
    drbd_free_one_sock(&connection->data)
      mutex_lock(&ds->mutex); --> line 2967

receive_protocol()
  mutex_lock(&connection->data.mutex); --> line 3778
  mutex_lock(&connection->resource->conf_update); --> line 3779

When drbd_adm_connect() and receive_protocol() are concurrently 
executed, the deadlock can occur.

I am not quite sure whether these possible deadlocks are real and how to 
fix them if they are real.
Any feedback would be appreciated, thanks

Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>


Best wishes,
Jia-Ju Bai