drbd: fix race between role change and handshake

Symptoms:
If DRBD was "cleanly shut down" (all in sync, both Secondary before
disconnect, identical data generation uuids), and then one side was
promoted *during* the next connection handshake, the role change
could confuse the handshake.

The Primary would get stuck in WFBitmapS, the Secondary would log
unexpected cstate (Connected) in receive_bitmap
and get stuck in WFBitmapT.

Fix:
The test in is_valid_soft_transition wrong. It works because
the not allowed actions (promote/attach) do not touch the
cstate. The previous condition failed to demand a cstate change
in one clause.

In order to avoid deadlocks give up the state_mutex while waiting
for the transient state to go away.

Conflicts:
	drbd/drbd_state.c
	drbd/drbd_state.h
	drbd/drbd_wrappers.h

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/drivers/block/drbd/drbd_state.h b/drivers/block/drbd/drbd_state.h
index cc41605ba21c..7f53c40823cd 100644
--- a/drivers/block/drbd/drbd_state.h
+++ b/drivers/block/drbd/drbd_state.h
@@ -117,6 +117,11 @@ extern enum drbd_state_rv _drbd_request_state(struct drbd_device *,
 					      union drbd_state,
 					      union drbd_state,
 					      enum chg_state_flags);
+
+extern enum drbd_state_rv
+_drbd_request_state_holding_state_mutex(struct drbd_device *, union drbd_state,
+					union drbd_state, enum chg_state_flags);
+
 extern enum drbd_state_rv __drbd_set_state(struct drbd_device *, union drbd_state,
 					   enum chg_state_flags,
 					   struct completion *done);