[Drbd-dev] DRBD-8 - after_state_ch() can attempt to terminate worker thread with wait==true

[Graham, Simon]

Near the end of after_state_ch() there are several clauses that stop
(and restart) receiver and worker threads synchronously - since this
function is called from both the worker and receiver thread context,
these calls cannot be made synchronously (and an ASSERT in
_drbd_thread_stop will fire).

There seem to be a couple of issues here:

1. Is it the intention that after_state_ch is always called from the
worker thread? If so, then the calls in drbd_receiver and
   drbd_fs need to change to submit work items

2. No matter what, it should not issue synchronous calls to
drbd_thread_stop for non-current threads.

3. In receive_state() -- should after_state_ch() be called at all if the
preceding call to _drbd_set_state fails? It seems a
   bit wrong to me to pass in the new state to after_state_ch when you
know this does not represent the actual new state...

4. Ditto receive_outdate().

Simon