Detect if we try to put a cell onto a supposedly blocked cell queue.

When this happens, run through the streams on the circuit and make
sure they're all blocked.  If some aren't, that's a bug: block them
all and log it!  If they all are, where did the cell come from?  Log
it!

(I suspect that this actually happens pretty frequently, so I'm making
these log messages appear at INFO.)

1 files changed, 24 insertions, 3 deletions

diff --git a/src/or/relay.c b/src/or/relay.c
index c123eb3973..88106e5d96 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -2100,12 +2100,16 @@ connection_or_unlink_all_active_circs(or_connection_t *orconn)
 
 /** Block (if <b>block</b> is true) or unblock (if <b>block</b> is false)
  * every edge connection that is using <b>circ</b> to write to <b>orconn</b>,
- * and start or stop reading as appropriate. */
-static void
+ * and start or stop reading as appropriate.
+ *
+ * Returns the number of streams whose status we changed.
+ */
+static int
 set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
                             int block)
 {
   edge_connection_t *edge = NULL;
+  int n = 0;
   if (circ->n_conn == orconn) {
     circ->streams_blocked_on_n_conn = block;
     if (CIRCUIT_IS_ORIGIN(circ))
@@ -2118,7 +2122,10 @@ set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
 
   for (; edge; edge = edge->next_stream) {
     connection_t *conn = TO_CONN(edge);
-    edge->edge_blocked_on_circ = block;
+    if (edge->edge_blocked_on_circ != block) {
+      ++n;
+      edge->edge_blocked_on_circ = block;
+    }
 
     if (!conn->read_event) {
       /* This connection is a placeholder for something; probably a DNS
@@ -2135,6 +2142,8 @@ set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
         connection_start_reading(conn);
     }
   }
+
+  return n;
 }
 
 /** Pull as many cells as possible (but no more than <b>max</b>) from the
@@ -2301,6 +2310,18 @@ append_cell_to_circuit_queue(circuit_t *circ, or_connection_t *orconn,
   if (!streams_blocked && queue->n >= CELL_QUEUE_HIGHWATER_SIZE)
     set_streams_blocked_on_circ(circ, orconn, 1); /* block streams */
 
+  if (streams_blocked) {
+    /* We must have missed a connection! */
+    int n = set_streams_blocked_on_circ(circ, orconn, 1);
+    if (n) {
+      log_info(LD_BUG, "Got a cell added to a cell queue when streams were "
+               "supposed to be blocked; found that %d streams weren't.", n);
+    } else {
+      log_info(LD_BUG, "Got a cell added to a cell queue when streams were "
+               "all blocked. We should figure out why.");
+    }
+  }
+
   if (queue->n == 1) {
     /* This was the first cell added to the queue.  We need to make this
      * circuit active. */