[BUG] drbd/block: A sleep-in-atomic bug in notify_helper

[Jia-Ju Bai]

The driver may sleep under a RCU lock, and the function call path is:
drbd_sync_handshake (acquire the RCU lock)
  drbd_asb_recover_1p
    drbd_khelper
      notify_helper
        mutex_lock --> may sleep

I hope to fix it, but I do not find a proper way at present ...
This bug is found by my static analysis tool and my code review.


Thanks,
Jia-Ju Bai