Revert #16288 (#25827)

src/core/ext/filters/client_channel/health/health_check_client.cc

@@ -269,11 +269,8 @@ HealthCheckClient::CallState::~CallState() {
   // Unset the call combiner cancellation closure.  This has the
   // effect of scheduling the previously set cancellation closure, if
   // any, so that it can release any internal references it may be
-  // holding to the call stack. Also flush the closures on exec_ctx so that
-  // filters that schedule cancel notification closures on exec_ctx do not
-  // need to take a ref of the call stack to guarantee closure liveness.
+  // holding to the call stack.
   call_combiner_.SetNotifyOnCancel(nullptr);
-  ExecCtx::Get()->Flush();
   arena_->Destroy();
 }
 

src/core/lib/iomgr/call_combiner.h

@@ -94,10 +94,6 @@ class CallCombiner {
   /// cancellation; this effectively unregisters the previously set closure.
   /// However, most filters will not need to explicitly unregister their
   /// callbacks, as this is done automatically when the call is destroyed.
-  /// Filters that schedule the cancellation closure on ExecCtx do not need
-  /// to take a ref on the call stack to guarantee closure liveness. This is
-  /// done by explicitly flushing ExecCtx after the unregistration during
-  /// call destruction.
   void SetNotifyOnCancel(grpc_closure* closure);
 
   /// Indicates that the call has been cancelled.

src/core/lib/security/transport/client_auth_filter.cc

@@ -232,6 +232,7 @@ static void cancel_get_request_metadata(void* arg, grpc_error* error) {
     calld->creds->cancel_get_request_metadata(&calld->md_array,
                                               GRPC_ERROR_REF(error));
   }
+  GRPC_CALL_STACK_UNREF(calld->owning_call, "cancel_get_request_metadata");
 }
 
 static void send_security_metadata(grpc_call_element* elem,
@@ -320,6 +321,9 @@ static void send_security_metadata(grpc_call_element* elem,
     GRPC_ERROR_UNREF(error);
   } else {
     // Async return; register cancellation closure with call combiner.
+    // TODO(yashykt): We would not need this ref if call combiners used
+    // Closure::Run() instead of ExecCtx::Run()
+    GRPC_CALL_STACK_REF(calld->owning_call, "cancel_get_request_metadata");
     calld->call_combiner->SetNotifyOnCancel(GRPC_CLOSURE_INIT(
         &calld->get_request_metadata_cancel_closure,
         cancel_get_request_metadata, elem, grpc_schedule_on_exec_ctx));
@@ -356,6 +360,7 @@ static void cancel_check_call_host(void* arg, grpc_error* error) {
     chand->security_connector->cancel_check_call_host(
         &calld->async_result_closure, GRPC_ERROR_REF(error));
   }
+  GRPC_CALL_STACK_UNREF(calld->owning_call, "cancel_check_call_host");
 }
 
 static void client_auth_start_transport_stream_op_batch(
@@ -390,6 +395,9 @@ static void client_auth_start_transport_stream_op_batch(
         GRPC_ERROR_UNREF(error);
       } else {
         // Async return; register cancellation closure with call combiner.
+        // TODO(yashykt): We would not need this ref if call combiners used
+        // Closure::Run() instead of ExecCtx::Run()
+        GRPC_CALL_STACK_REF(calld->owning_call, "cancel_check_call_host");
         calld->call_combiner->SetNotifyOnCancel(GRPC_CLOSURE_INIT(
             &calld->check_call_host_cancel_closure, cancel_check_call_host,
             elem, grpc_schedule_on_exec_ctx));

src/core/lib/security/transport/server_auth_filter.cc

@@ -206,6 +206,7 @@ static void cancel_call(void* arg, grpc_error* error) {
     on_md_processing_done_inner(elem, nullptr, 0, nullptr, 0,
                                 GRPC_ERROR_REF(error));
   }
+  GRPC_CALL_STACK_UNREF(calld->owning_call, "cancel_call");
 }
 
 static void recv_initial_metadata_ready(void* arg, grpc_error* error) {
@@ -218,6 +219,9 @@ static void recv_initial_metadata_ready(void* arg, grpc_error* error) {
         chand->creds->auth_metadata_processor().process != nullptr) {
       // We're calling out to the application, so we need to make sure
       // to drop the call combiner early if we get cancelled.
+      // TODO(yashykt): We would not need this ref if call combiners used
+      // Closure::Run() instead of ExecCtx::Run()
+      GRPC_CALL_STACK_REF(calld->owning_call, "cancel_call");
       GRPC_CLOSURE_INIT(&calld->cancel_closure, cancel_call, elem,
                         grpc_schedule_on_exec_ctx);
       calld->call_combiner->SetNotifyOnCancel(&calld->cancel_closure);

src/core/lib/surface/call.cc

@@ -610,11 +610,8 @@ void grpc_call_unref(grpc_call* c) {
     // Unset the call combiner cancellation closure.  This has the
     // effect of scheduling the previously set cancellation closure, if
     // any, so that it can release any internal references it may be
-    // holding to the call stack. Also flush the closures on exec_ctx so that
-    // filters that schedule cancel notification closures on exec_ctx do not
-    // need to take a ref of the call stack to guarantee closure liveness.
+    // holding to the call stack.
     c->call_combiner.SetNotifyOnCancel(nullptr);
-    grpc_core::ExecCtx::Get()->Flush();
   }
   GRPC_CALL_INTERNAL_UNREF(c, "destroy");
 }