Fixes to subchannel and its index

src/core/ext/filters/client_channel/subchannel.c

@@ -283,6 +283,7 @@ static void disconnect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
 void grpc_subchannel_unref(grpc_exec_ctx *exec_ctx,
                            grpc_subchannel *c GRPC_SUBCHANNEL_REF_EXTRA_ARGS) {
   gpr_atm old_refs;
+  // add a weak ref and subtract a strong ref (atomically)
   old_refs = ref_mutate(c, (gpr_atm)1 - (gpr_atm)(1 << INTERNAL_REF_BITS),
                         1 REF_MUTATE_PURPOSE("STRONG_UNREF"));
   if ((old_refs & STRONG_REF_MASK) == (1 << INTERNAL_REF_BITS)) {
@@ -656,7 +657,6 @@ static bool publish_transport_locked(grpc_exec_ctx *exec_ctx,
     gpr_free(sw_subchannel);
     grpc_channel_stack_destroy(exec_ctx, stk);
     gpr_free(con);
-    GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, c, "connecting");
     return false;
   }
 

src/core/ext/filters/client_channel/subchannel_index.c

@@ -183,8 +183,11 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
   enter_ctx(exec_ctx);
 
   grpc_subchannel *c = NULL;
+  bool need_to_unref_constructed;
 
   while (c == NULL) {
+    need_to_unref_constructed = false;
+
     // Compare and swap loop:
     // - take a reference to the current index
     gpr_mu_lock(&g_mu);
@@ -193,9 +196,12 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
 
     // - Check to see if a subchannel already exists
     c = gpr_avl_get(index, key);
+    if (c != NULL) {
+      c = GRPC_SUBCHANNEL_REF_FROM_WEAK_REF(c, "index_register");
+    }
     if (c != NULL) {
       // yes -> we're done
-      GRPC_SUBCHANNEL_WEAK_UNREF(exec_ctx, constructed, "index_register");
+      need_to_unref_constructed = true;
     } else {
       // no -> update the avl and compare/swap
       gpr_avl updated =
@@ -219,6 +225,10 @@ grpc_subchannel *grpc_subchannel_index_register(grpc_exec_ctx *exec_ctx,
 
   leave_ctx(exec_ctx);
 
+  if (need_to_unref_constructed) {
+    GRPC_SUBCHANNEL_UNREF(exec_ctx, constructed, "index_register");
+  }
+
   return c;
 }