drbd: Delay/reject other state changes while establishing a connection

Changes to the role and disk state should be delayed or rejected
while we establish a connection.

This is necessary, since the peer will base its resync decision
on the UUIDs and the state we sent in the drbd_connect() function.

The most prominent example for this race is becoming primary after
sending state and UUIDs and before the state changes to C_WF_CONNECTION.

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

drivers/block/drbd/drbd_int.h

@@ -850,6 +850,7 @@ enum {
 	NEW_CUR_UUID,		/* Create new current UUID when thawing IO */
 	AL_SUSPENDED,		/* Activity logging is currently suspended. */
 	AHEAD_TO_SYNC_SOURCE,   /* Ahead -> SyncSource queued */
+	STATE_SENT,		/* Do not change state/UUIDs while this is set */
 };
 
 struct drbd_bitmap; /* opaque for drbd_conf */

drivers/block/drbd/drbd_main.c

@@ -841,6 +841,13 @@ is_valid_state_transition(struct drbd_conf *mdev, union drbd_state ns,
 	if (ns.conn == os.conn && ns.conn == C_WF_REPORT_PARAMS)
 		rv = SS_IN_TRANSIENT_STATE;
 
+	/* While establishing a connection only allow cstate to change.
+	   Delay/refuse role changes, detach attach etc... */
+	if (test_bit(STATE_SENT, &mdev->flags) &&
+	    !(os.conn == C_WF_REPORT_PARAMS ||
+	      (ns.conn == C_WF_REPORT_PARAMS && os.conn == C_WF_CONNECTION)))
+		rv = SS_IN_TRANSIENT_STATE;
+
 	if ((ns.conn == C_VERIFY_S || ns.conn == C_VERIFY_T) && os.conn < C_CONNECTED)
 		rv = SS_NEED_CONNECTION;
 
@@ -1668,6 +1675,12 @@ static void after_state_ch(struct drbd_conf *mdev, union drbd_state os,
 	if (os.disk < D_UP_TO_DATE && os.conn >= C_SYNC_SOURCE && ns.conn == C_CONNECTED)
 		drbd_send_state(mdev, ns);
 
+	/* Wake up role changes, that were delayed because of connection establishing */
+	if (os.conn == C_WF_REPORT_PARAMS && ns.conn != C_WF_REPORT_PARAMS) {
+		clear_bit(STATE_SENT, &mdev->flags);
+		wake_up(&mdev->state_wait);
+	}
+
 	/* This triggers bitmap writeout of potentially still unwritten pages
 	 * if the resync finished cleanly, or aborted because of peer disk
 	 * failure, or because of connection loss.

drivers/block/drbd/drbd_nl.c

@@ -289,7 +289,7 @@ static int _try_outdate_peer_async(void *data)
 	*/
 	spin_lock_irq(&mdev->req_lock);
 	ns = mdev->state;
-	if (ns.conn < C_WF_REPORT_PARAMS) {
+	if (ns.conn < C_WF_REPORT_PARAMS && !test_bit(STATE_SENT, &mdev->flags)) {
 		ns.pdsk = nps;
 		_drbd_set_state(mdev, ns, CS_VERBOSE, NULL);
 	}

drivers/block/drbd/drbd_receiver.c

@@ -751,6 +751,7 @@ static int drbd_connect(struct drbd_conf *mdev)
 {
 	struct socket *s, *sock, *msock;
 	int try, h, ok;
+	enum drbd_state_rv rv;
 
 	D_ASSERT(!mdev->data.socket);
 
@@ -897,6 +898,7 @@ retry:
 
 	if (drbd_send_protocol(mdev) == -1)
 		return -1;
+	set_bit(STATE_SENT, &mdev->flags);
 	drbd_send_sync_param(mdev, &mdev->sync_conf);
 	drbd_send_sizes(mdev, 0, 0);
 	drbd_send_uuids(mdev);
@@ -904,7 +906,13 @@ retry:
 	clear_bit(USE_DEGR_WFC_T, &mdev->flags);
 	clear_bit(RESIZE_PENDING, &mdev->flags);
 
-	if (drbd_request_state(mdev, NS(conn, C_WF_REPORT_PARAMS)) < SS_SUCCESS)
+	spin_lock_irq(&mdev->req_lock);
+	rv = _drbd_set_state(_NS(mdev, conn, C_WF_REPORT_PARAMS), CS_VERBOSE, NULL);
+	if (mdev->state.conn != C_WF_REPORT_PARAMS)
+		clear_bit(STATE_SENT, &mdev->flags);
+	spin_unlock_irq(&mdev->req_lock);
+
+	if (rv < SS_SUCCESS)
 		return 0;
 
 	drbd_thread_start(&mdev->asender);