Fix accept_stream being called post-channel deletion

- Have the server clear the accept_stream callback prior to destroying
  the channel (required a small transport op protocol change)
- Have the transport not enact transport ops until parsing is completed
  (prevents accept_stream from disappearing mid-parse)

src/core/channel/client_channel.c

@@ -251,7 +251,7 @@ static void cc_start_transport_op(grpc_exec_ctx *exec_ctx,
 
   grpc_exec_ctx_enqueue(exec_ctx, op->on_consumed, true, NULL);
 
-  GPR_ASSERT(op->set_accept_stream == NULL);
+  GPR_ASSERT(op->set_accept_stream == false);
   if (op->bind_pollset != NULL) {
     grpc_pollset_set_add_pollset(exec_ctx, chand->interested_parties,
                                  op->bind_pollset);

src/core/channel/client_uchannel.c

@@ -107,7 +107,7 @@ static void cuc_start_transport_op(grpc_exec_ctx *exec_ctx,
 
   grpc_exec_ctx_enqueue(exec_ctx, op->on_consumed, true, NULL);
 
-  GPR_ASSERT(op->set_accept_stream == NULL);
+  GPR_ASSERT(op->set_accept_stream == false);
   GPR_ASSERT(op->bind_pollset == NULL);
 
   if (op->on_connectivity_state_change != NULL) {

src/core/surface/server.c

@@ -407,8 +407,15 @@ static void destroy_channel(grpc_exec_ctx *exec_ctx, channel_data *chand) {
   maybe_finish_shutdown(exec_ctx, chand->server);
   chand->finish_destroy_channel_closure.cb = finish_destroy_channel;
   chand->finish_destroy_channel_closure.cb_arg = chand;
-  grpc_exec_ctx_enqueue(exec_ctx, &chand->finish_destroy_channel_closure, true,
-                        NULL);
+
+  grpc_transport_op op;
+  memset(&op, 0, sizeof(op));
+  op.set_accept_stream = true;
+  op.on_consumed = &chand->finish_destroy_channel_closure;
+  grpc_channel_next_op(exec_ctx,
+                       grpc_channel_stack_element(
+                           grpc_channel_get_channel_stack(chand->channel), 0),
+                       &op);
 }
 
 static void finish_start_new_rpc(grpc_exec_ctx *exec_ctx, grpc_server *server,
@@ -971,7 +978,8 @@ void grpc_server_setup_transport(grpc_exec_ctx *exec_ctx, grpc_server *s,
 
   GRPC_CHANNEL_INTERNAL_REF(channel, "connectivity");
   memset(&op, 0, sizeof(op));
-  op.set_accept_stream = accept_stream;
+  op.set_accept_stream = true;
+  op.set_accept_stream_fn = accept_stream;
   op.set_accept_stream_user_data = chand;
   op.on_connectivity_state_change = &chand->channel_connectivity_changed;
   op.connectivity_state = &chand->connectivity_state;

src/core/transport/chttp2/internal.h

@@ -358,6 +358,9 @@ struct grpc_chttp2_transport {
     /** connectivity tracking */
     grpc_connectivity_state_tracker state_tracker;
   } channel_callback;
+
+  /** Transport op to be applied post-parsing */
+  grpc_transport_op *post_parsing_op;
 };
 
 typedef struct {

src/core/transport/chttp2_transport.c

@@ -951,12 +951,10 @@ void grpc_chttp2_ack_ping(grpc_exec_ctx *exec_ctx,
   unlock(exec_ctx, t);
 }
 
-static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
-                                 grpc_transport_op *op) {
-  grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
-  int close_transport = 0;
-
-  lock(t);
+static void perform_transport_op_locked(grpc_exec_ctx *exec_ctx,
+                                        grpc_chttp2_transport *t,
+                                        grpc_transport_op *op) {
+  bool close_transport = false;
 
   grpc_exec_ctx_enqueue(exec_ctx, op->on_consumed, true, NULL);
 
@@ -975,8 +973,8 @@ static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
     close_transport = !grpc_chttp2_has_streams(t);
   }
 
-  if (op->set_accept_stream != NULL) {
-    t->channel_callback.accept_stream = op->set_accept_stream;
+  if (op->set_accept_stream) {
+    t->channel_callback.accept_stream = op->set_accept_stream_fn;
     t->channel_callback.accept_stream_user_data =
         op->set_accept_stream_user_data;
   }
@@ -997,15 +995,29 @@ static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
     close_transport_locked(exec_ctx, t);
   }
 
-  unlock(exec_ctx, t);
-
   if (close_transport) {
-    lock(t);
     close_transport_locked(exec_ctx, t);
-    unlock(exec_ctx, t);
   }
 }
 
+static void perform_transport_op(grpc_exec_ctx *exec_ctx, grpc_transport *gt,
+                                 grpc_transport_op *op) {
+  grpc_chttp2_transport *t = (grpc_chttp2_transport *)gt;
+
+  lock(t);
+
+  /* Let's be overly cautious: don't change any state while we're parsing */
+  if (t->parsing_active) {
+    GPR_ASSERT(t->post_parsing_op == NULL);
+    t->post_parsing_op = gpr_malloc(sizeof(*op));
+    memcpy(t->post_parsing_op, op, sizeof(*op));
+  } else {
+    perform_transport_op_locked(exec_ctx, t, op);
+  }
+
+  unlock(exec_ctx, t);
+}
+
 /*******************************************************************************
  * INPUT PROCESSING
  */
@@ -1401,6 +1413,13 @@ static void recv_data(grpc_exec_ctx *exec_ctx, void *tp, bool success) {
     /* handle higher level things */
     grpc_chttp2_publish_reads(exec_ctx, transport_global, transport_parsing);
     t->parsing_active = 0;
+    /* handle delayed transport ops (if there is one) */
+    if (t->post_parsing_op) {
+      grpc_transport_op *op = t->post_parsing_op;
+      t->post_parsing_op = NULL;
+      perform_transport_op_locked(exec_ctx, t, op);
+      gpr_free(op);
+    }
     /* if a stream is in the stream map, and gets cancelled, we need to ensure
      * we are not parsing before continuing the cancellation to keep things in
      * a sane state */

src/core/transport/transport.h

@@ -139,8 +139,10 @@ typedef struct grpc_transport_op {
   gpr_slice *goaway_message;
   /** set the callback for accepting new streams;
       this is a permanent callback, unlike the other one-shot closures */
-  void (*set_accept_stream)(grpc_exec_ctx *exec_ctx, void *user_data,
-                            grpc_transport *transport, const void *server_data);
+  bool set_accept_stream;
+  void (*set_accept_stream_fn)(grpc_exec_ctx *exec_ctx, void *user_data,
+                               grpc_transport *transport,
+                               const void *server_data);
   void *set_accept_stream_user_data;
   /** add this transport to a pollset */
   grpc_pollset *bind_pollset;