btrack_orconn slowly leaks memory

Over about 6 days, bto_find_or_new memory usage on a busy relay as reported by gperftools increased from ~13 MB to ~53 MB, or ~6.5 MB/day, ~200 MB/month. The number of open connections increased from about 6000 to 8000 over the 6 days. On another relay, manually calling bto_clear_maps and bto_init_maps freed 120 MB, as measured by or_metrics. The relay had been up for 14 days, so btrack_orconn used about 8.5 MB/day, including connections which were still open at the time of manual clearing.

I don't know why this memory is leaked. Doing some quick tests with ss -K on a client, bto_delete seems to be called appropriately. I suppose either there exists some case(s) where either bto_delete is not called or bto_delete does not free all the memory, but bto_clear_maps does.

More broadly, though, it seems like btrack could stop tracking connections once bootstrapping is completed. That's probably easier than fixing the memory leak. I have written this hack to do that:

diff --git a/src/feature/control/btrack_orconn.c b/src/feature/control/btrack_orconn.c
index 8b1b5788d0..fbee374693 100644
--- a/src/feature/control/btrack_orconn.c
+++ b/src/feature/control/btrack_orconn.c
@@ -121,6 +121,9 @@ bto_state_rcvr(const msg_t *msg, const orconn_state_msg_t *arg)
 
   (void)msg;
   bto = bto_find_or_new(arg->gid, arg->chan);
+  if (!bto)
+    return;
+
   log_debug(LD_BTRACK, "ORCONN gid=%"PRIu64" chan=%"PRIu64
             " proxy_type=%d state=%d",
             arg->gid, arg->chan, arg->proxy_type, arg->state);
@@ -162,6 +165,9 @@ bto_chan_rcvr(const msg_t *msg, const ocirc_chan_msg_t *arg)
 
   (void)msg;
   bto = bto_find_or_new(0, arg->chan);
+  if (!bto)
+    return;
+
   if (!bto->is_orig || (bto->is_onehop && !arg->onehop)) {
     log_debug(LD_BTRACK, "ORCONN LAUNCH chan=%"PRIu64" onehop=%d",
               arg->chan, arg->onehop);
diff --git a/src/feature/control/btrack_orconn_cevent.c b/src/feature/control/btrack_orconn_cevent.c
index 525f4f5d0d..be7162c9aa 100644
--- a/src/feature/control/btrack_orconn_cevent.c
+++ b/src/feature/control/btrack_orconn_cevent.c
@@ -20,6 +20,7 @@
 #include "core/or/orconn_event.h"
 #include "feature/control/btrack_orconn.h"
 #include "feature/control/btrack_orconn_cevent.h"
+#include "feature/control/btrack_orconn_maps.h"
 #include "feature/control/control_events.h"
 
 /**
@@ -147,6 +148,7 @@ bto_cevent_apconn(const bt_orconn_t *bto)
     break;
   case OR_CONN_STATE_OPEN:
     control_event_bootstrap(BOOTSTRAP_STATUS_AP_HANDSHAKE_DONE, 0);
+    bto_clear_maps();
     break;
   default:
     break;
diff --git a/src/feature/control/btrack_orconn_maps.c b/src/feature/control/btrack_orconn_maps.c
index 2b458d5826..400fe0024b 100644
--- a/src/feature/control/btrack_orconn_maps.c
+++ b/src/feature/control/btrack_orconn_maps.c
@@ -68,6 +68,9 @@ bto_gid_clear_map(void)
 {
   bt_orconn_t **elt, **next, *c;
 
+  if (!bto_gid_map)
+    return;
+
   for (elt = HT_START(bto_gid_ht, bto_gid_map);
        elt;
        elt = next) {
@@ -90,6 +93,9 @@ bto_chan_clear_map(void)
 {
   bt_orconn_t **elt, **next, *c;
 
+  if (!bto_chan_map)
+    return;
+
   for (elt = HT_START(bto_chan_ht, bto_chan_map);
        elt;
        elt = next) {
@@ -188,6 +194,9 @@ bto_new(const bt_orconn_t *key)
 bt_orconn_t *
 bto_find_or_new(uint64_t gid, uint64_t chan)
 {
+  if (!bto_gid_map)
+    return NULL;
+
   bt_orconn_t key, *bto = NULL;
 
   tor_assert(gid || chan);