libceph: fix msgr standby handling

The standby logic used to be pretty dependent on the work requeueing
behavior that changed when we switched to WQ_NON_REENTRANT. It was also
very fragile.

Restructure things so that:
- We clear WRITE_PENDING when we set STANDBY. This ensures we will
requeue work when we wake up later.
- con_work backs off if STANDBY is set. There is nothing to do if we are
in standby.
- clear_standby() helper is called by both con_send() and con_keepalive(),
the two actions that can wake us up again. Move the connect_seq++
logic here.

Signed-off-by: Sage Weil <[e-mail]>

net/ceph/messenger.c

···
 
 	/* open the socket first? */
 	if (con->sock == NULL) {
-		/*
-		 * if we were STANDBY and are reconnecting _this_
-		 * connection, bump connect_seq now.  Always bump
-		 * global_seq.
-		 */
-		if (test_and_clear_bit(STANDBY, &con->state))
-			con->connect_seq++;
-
 		prepare_write_banner(msgr, con);
 		prepare_write_connect(msgr, con, 1);
 		prepare_read_banner(con);
···
 		}
 	}
 
+	if (test_bit(STANDBY, &con->state)) {
+		dout("con_work %p STANDBY\n", con);
+		goto done;
+	}
 	if (test_bit(CLOSED, &con->state)) { /* e.g. if we are replaced */
 		dout("con_work CLOSED\n");
 		con_close_socket(con);
···
 	 * the connection in a STANDBY state */
 	if (list_empty(&con->out_queue) &&
 	    !test_bit(KEEPALIVE_PENDING, &con->state)) {
+		dout("fault %p setting STANDBY clearing WRITE_PENDING\n", con);
+		clear_bit(WRITE_PENDING, &con->state);
 		set_bit(STANDBY, &con->state);
 	} else {
 		/* retry after a delay. */
···
 }
 EXPORT_SYMBOL(ceph_messenger_destroy);
 
+static void clear_standby(struct ceph_connection *con)
+{
+	/* come back from STANDBY? */
+	if (test_and_clear_bit(STANDBY, &con->state)) {
+		mutex_lock(&con->mutex);
+		dout("clear_standby %p and ++connect_seq\n", con);
+		con->connect_seq++;
+		WARN_ON(test_bit(WRITE_PENDING, &con->state));
+		WARN_ON(test_bit(KEEPALIVE_PENDING, &con->state));
+		mutex_unlock(&con->mutex);
+	}
+}
+
 /*
  * Queue up an outgoing message on the given connection.
  */
···
 
 	/* if there wasn't anything waiting to send before, queue
 	 * new work */
+	clear_standby(con);
 	if (test_and_set_bit(WRITE_PENDING, &con->state) == 0)
 		queue_con(con);
 }
···
  */
 void ceph_con_keepalive(struct ceph_connection *con)
 {
+	dout("con_keepalive %p\n", con);
+	clear_standby(con);
 	if (test_and_set_bit(KEEPALIVE_PENDING, &con->state) == 0 &&
 	    test_and_set_bit(WRITE_PENDING, &con->state) == 0)
 		queue_con(con);