From a03469aa851bf6e658d539e95b5f1e786f9622bc Mon Sep 17 00:00:00 2001
From: Nick Mathewson <nickm@torproject.org>
Date: Wed, 16 Dec 2015 08:37:40 -0500
Subject: [PATCH] More debugging code to try to track down #17659

---
 src/or/connection_edge.c | 31 ++++++++++++++++++++++++++++---
 src/or/or.h              |  7 +++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/src/or/connection_edge.c b/src/or/connection_edge.c
index 7a2de29601..961e49abd9 100644
--- a/src/or/connection_edge.c
+++ b/src/or/connection_edge.c
@@ -780,6 +780,15 @@ connection_ap_rescan_and_attach_pending(void)
   connection_ap_attach_pending(1);
 }
 
+#ifdef DEBUGGING_17659
+#define UNMARK() do {                           \
+    entry_conn->marked_pending_circ_line = 0;   \
+    entry_conn->marked_pending_circ_file = 0;   \
+  } while (0)
+#else
+#define UNMARK() do { } while (0)
+#endif
+
 /** Tell any AP streams that are listed as waiting for a new circuit to try
  * again, either attaching to an available circ or launching a new one.
  *
@@ -801,12 +810,14 @@ connection_ap_attach_pending(int retry)
     connection_t *conn = ENTRY_TO_CONN(entry_conn);
     tor_assert(conn && entry_conn);
     if (conn->marked_for_close) {
+      UNMARK();
       SMARTLIST_DEL_CURRENT(pending_entry_connections, entry_conn);
       continue;
     }
     if (conn->magic != ENTRY_CONNECTION_MAGIC) {
-      log_warn(LD_BUG, "%p has impossible magic value %u",
+      log_warn(LD_BUG, "%p has impossible magic value %u.",
                entry_conn, (unsigned)conn->magic);
+      UNMARK();
       SMARTLIST_DEL_CURRENT(pending_entry_connections, entry_conn);
       continue;
     }
@@ -815,6 +826,7 @@ connection_ap_attach_pending(int retry)
                "is %s. Why is it on pending_entry_connections?",
                entry_conn,
                conn_state_to_string(conn->type, conn->state));
+      UNMARK();
       SMARTLIST_DEL_CURRENT(pending_entry_connections, entry_conn);
       continue;
     }
@@ -828,6 +840,7 @@ connection_ap_attach_pending(int retry)
     if (conn->marked_for_close ||
         conn->type != CONN_TYPE_AP ||
         conn->state != AP_CONN_STATE_CIRCUIT_WAIT) {
+      UNMARK();
       SMARTLIST_DEL_CURRENT(pending_entry_connections, entry_conn);
       continue;
     }
@@ -862,12 +875,23 @@ connection_ap_mark_as_pending_circuit_(entry_connection_t *entry_conn,
   if (PREDICT_UNLIKELY(smartlist_contains(pending_entry_connections,
                                           entry_conn))) {
     log_warn(LD_BUG, "What?? pending_entry_connections already contains %p! "
-             "(called from %s:%d)",
+             "(Called from %s:%d.)",
              entry_conn, fname, lineno);
-    log_backtrace(LOG_WARN, LD_BUG, "To debug, this may help.");
+#ifdef DEBUGGING_17659
+    const char *f2 = entry_conn->marked_pending_circ_file;
+    log_warn(LD_BUG, "(Previously called from %s:%d.)\n",
+             f2 ? f2 : "<NULL>",
+             entry_conn->marked_pending_circ_line);
+#endif
+    log_backtrace(LOG_WARN, LD_BUG, "To debug, this may help");
     return;
   }
 
+#ifdef DEBUGGING_17659
+  entry_conn->marked_pending_circ_line = (uint16_t) lineno;
+  entry_conn->marked_pending_circ_file = fname;
+#endif
+
   untried_pending_connections = 1;
   smartlist_add(pending_entry_connections, entry_conn);
 }
@@ -878,6 +902,7 @@ connection_ap_mark_as_non_pending_circuit(entry_connection_t *entry_conn)
 {
   if (PREDICT_UNLIKELY(NULL == pending_entry_connections))
     return;
+  UNMARK();
   smartlist_remove(pending_entry_connections, entry_conn);
 }
 
diff --git a/src/or/or.h b/src/or/or.h
index e92a4bba39..e621fe9708 100644
--- a/src/or/or.h
+++ b/src/or/or.h
@@ -1646,6 +1646,13 @@ typedef struct entry_connection_t {
    * request that we're going to try to answer.  */
   struct evdns_server_request *dns_server_request;
 
+#define DEBUGGING_17659
+
+#ifdef DEBUGGING_17659
+  uint16_t marked_pending_circ_line;
+  const char *marked_pending_circ_file;
+#endif
+
 #define NUM_CIRCUITS_LAUNCHED_THRESHOLD 10
   /** Number of times we've launched a circuit to handle this stream. If
     * it gets too high, that could indicate an inconsistency between our