[PATCH 2/2] drbd: send state before bitmap to avoid receive_bitmap race

["zhengbing.huang" <zhengbing.huang@easystack.cn>]

When a node becomes SyncSource (L_WF_BITMAP_S), after_state_chg() on the
worker thread queues the bitmap send while receive_state() on the receiver
thread sends the P_STATE that lets the peer reach L_WF_BITMAP_T. These race,
so the bitmap can arrive while the peer is still L_ESTABLISHED and get
dropped in receive_bitmap(), logging "unexpected repl_state (Established) in
receive_bitmap".

Send the current state synchronously before queueing the bitmap so the peer
transitions to L_WF_BITMAP_T first.

Signed-off-by: zhengbing.huang <zhengbing.huang@easystack.cn>
---
 drbd/drbd_state.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drbd/drbd_state.c b/drbd/drbd_state.c
index 4ddb31cb8..65414a774 100644
--- a/drbd/drbd_state.c
+++ b/drbd/drbd_state.c
@@ -4884,6 +4884,12 @@ static int w_after_state_change(struct drbd_work *w, int unused)
 				 * it does no harm to resync a small amount of
 				 * additional data. */
 				drbd_set_pending_out_of_sync(peer_device);
+				/* Tell the peer about our new state before sending the
+				 * bitmap, so it can reach L_WF_BITMAP_T first. Otherwise
+				 * the bitmap may arrive while the peer is still
+				 * L_ESTABLISHED and get dropped in receive_bitmap().
+				 */
+				drbd_send_state(peer_device, new_state);
 				/* ldev_safe: ref from extra_ldev_ref_for_after_state_chg() */
 				drbd_queue_bitmap_io(device, &drbd_send_bitmap, NULL,
 						"send_bitmap (WFBitMapS)",
-- 
2.43.0