[tor-commits] [tor/maint-0.2.8] When clearing cells from a circuit for OOM reasons, tell cmux we did so.

[nickm@xxxxxxxxxxxxxx]

commit e4aaf7666028c30866ad63053ad9f6eb6bf16bf7
Author: Nick Mathewson <nickm@xxxxxxxxxxxxxx>
Date:   Wed Sep 21 19:01:12 2016 -0400

    When clearing cells from a circuit for OOM reasons, tell cmux we did so.
    
    Not telling the cmux would sometimes cause an assertion failure in
    relay.c when we tried to get an active circuit and found an "active"
    circuit with no cells.
    
    Additionally, replace that assert with a test and a log message.
    
    Fix for bug 20203. This is actually probably a bugfix on
    0.2.8.1-alpha, specifically my code in 8b4e5b7ee902fb7fa0776 where I
    made circuit_mark_for_close_() do less in order to simplify our call
    graph. Thanks to "cypherpunks" for help diagnosing.
---
 changes/bug20203     |  6 ++++++
 src/or/circuitlist.c | 10 ++++++++--
 src/or/relay.c       |  9 +++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/changes/bug20203 b/changes/bug20203
new file mode 100644
index 0000000..b4809ff
--- /dev/null
+++ b/changes/bug20203
@@ -0,0 +1,6 @@
+  o Major bugfixes (relay, OOM handler)
+    - Fix a timing-dependent assertion failure that could occur when we
+      tried to flush from a circuit after having freed its cells because
+      of an out-of-memory condition. Fixes bug 20203; bugfix on
+      0.2.8.1-alpha. Thanks to "cypherpunks" for help diagnosing this
+      one.
diff --git a/src/or/circuitlist.c b/src/or/circuitlist.c
index 716024d..5fb8be5 100644
--- a/src/or/circuitlist.c
+++ b/src/or/circuitlist.c
@@ -1836,8 +1836,14 @@ marked_circuit_free_cells(circuit_t *circ)
     return;
   }
   cell_queue_clear(&circ->n_chan_cells);
-  if (! CIRCUIT_IS_ORIGIN(circ))
-    cell_queue_clear(& TO_OR_CIRCUIT(circ)->p_chan_cells);
+  if (circ->n_mux)
+    circuitmux_clear_num_cells(circ->n_mux, circ);
+  if (! CIRCUIT_IS_ORIGIN(circ)) {
+    or_circuit_t *orcirc = TO_OR_CIRCUIT(circ);
+    cell_queue_clear(&orcirc->p_chan_cells);
+    if (orcirc->p_mux)
+      circuitmux_clear_num_cells(orcirc->p_mux, circ);
+  }
 }
 
 static size_t
diff --git a/src/or/relay.c b/src/or/relay.c
index eddad6a..33191e1 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -2619,6 +2619,15 @@ channel_flush_from_first_active_circuit, (channel_t *chan, int max))
     }
 
     /* Circuitmux told us this was active, so it should have cells */
+    if (/*BUG(*/ queue->n == 0 /*)*/) {
+      log_warn(LD_BUG, "Found a supposedly active circuit with no cells "
+               "to send. Trying to recover.");
+      circuitmux_set_num_cells(cmux, circ, 0);
+      if (! circ->marked_for_close)
+        circuit_mark_for_close(circ, END_CIRC_REASON_INTERNAL);
+      continue;
+    }
+
     tor_assert(queue->n > 0);
 
     /*



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