Fix race in call.c

src/core/lib/surface/call.c

@@ -101,6 +101,17 @@ typedef struct {
   grpc_error *error;
 } received_status;
 
+static gpr_atm pack_received_status(received_status r) {
+  return r.is_set ? (1 | (gpr_atm)r.error) : 0;
+}
+
+static received_status unpack_received_status(gpr_atm atm) {
+  return (atm & 1) == 0
+             ? (received_status){.is_set = false, .error = GRPC_ERROR_NONE}
+             : (received_status){.is_set = true,
+                                 .error = (grpc_error *)(atm & ~(gpr_atm)1)};
+}
+
 #define MAX_ERRORS_PER_BATCH 3
 
 typedef struct batch_control {
@@ -165,8 +176,8 @@ struct grpc_call {
      Element 0 is initial metadata, element 1 is trailing metadata. */
   grpc_metadata_array *buffered_metadata[2];
 
-  /* Received call statuses from various sources */
-  received_status status[STATUS_SOURCE_COUNT];
+  /* Packed received call statuses from various sources */
+  gpr_atm status[STATUS_SOURCE_COUNT];
 
   /* Call data useful used for reporting. Only valid after the call has
    * completed */
@@ -446,7 +457,8 @@ static void destroy_call(grpc_exec_ctx *exec_ctx, void *call,
       gpr_time_sub(gpr_now(GPR_CLOCK_MONOTONIC), c->start_time);
 
   for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-    GRPC_ERROR_UNREF(c->status[i].error);
+    GRPC_ERROR_UNREF(
+        unpack_received_status(gpr_atm_no_barrier_load(&c->status[i])).error);
   }
 
   grpc_call_stack_destroy(exec_ctx, CALL_STACK_FROM_CALL(c), &c->final_info, c);
@@ -614,13 +626,12 @@ static void cancel_with_status(grpc_exec_ctx *exec_ctx, grpc_call *c,
  */
 
 static bool get_final_status_from(
-    grpc_call *call, status_source from_source, bool allow_ok_status,
+    grpc_call *call, grpc_error *error, bool allow_ok_status,
     void (*set_value)(grpc_status_code code, void *user_data),
     void *set_value_user_data, grpc_slice *details) {
   grpc_status_code code;
   const char *msg = NULL;
-  grpc_error_get_status(call->status[from_source].error, call->send_deadline,
-                        &code, &msg, NULL);
+  grpc_error_get_status(error, call->send_deadline, &code, &msg, NULL);
   if (code == GRPC_STATUS_OK && !allow_ok_status) {
     return false;
   }
@@ -638,12 +649,15 @@ static void get_final_status(grpc_call *call,
                                                void *user_data),
                              void *set_value_user_data, grpc_slice *details) {
   int i;
+  received_status status[STATUS_SOURCE_COUNT];
+  for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
+    status[i] = unpack_received_status(gpr_atm_acq_load(&call->status[i]));
+  }
   if (grpc_call_error_trace) {
     gpr_log(GPR_DEBUG, "get_final_status %s", call->is_client ? "CLI" : "SVR");
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set) {
-        gpr_log(GPR_DEBUG, "  %d: %s", i,
-                grpc_error_string(call->status[i].error));
+      if (status[i].is_set) {
+        gpr_log(GPR_DEBUG, "  %d: %s", i, grpc_error_string(status[i].error));
       }
     }
   }
@@ -653,9 +667,9 @@ static void get_final_status(grpc_call *call,
     /* search for the best status we can present: ideally the error we use has a
        clearly defined grpc-status, and we'll prefer that. */
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set &&
-          grpc_error_has_clear_grpc_status(call->status[i].error)) {
-        if (get_final_status_from(call, (status_source)i, allow_ok_status != 0,
+      if (status[i].is_set &&
+          grpc_error_has_clear_grpc_status(status[i].error)) {
+        if (get_final_status_from(call, status[i].error, allow_ok_status != 0,
                                   set_value, set_value_user_data, details)) {
           return;
         }
@@ -663,8 +677,8 @@ static void get_final_status(grpc_call *call,
     }
     /* If no clearly defined status exists, search for 'anything' */
     for (i = 0; i < STATUS_SOURCE_COUNT; i++) {
-      if (call->status[i].is_set) {
-        if (get_final_status_from(call, (status_source)i, allow_ok_status != 0,
+      if (status[i].is_set) {
+        if (get_final_status_from(call, status[i].error, allow_ok_status != 0,
                                   set_value, set_value_user_data, details)) {
           return;
         }
@@ -681,12 +695,13 @@ static void get_final_status(grpc_call *call,
 
 static void set_status_from_error(grpc_exec_ctx *exec_ctx, grpc_call *call,
                                   status_source source, grpc_error *error) {
-  if (call->status[source].is_set) {
+  if (!gpr_atm_rel_cas(&call->status[source],
+                       pack_received_status((received_status){
+                           .is_set = false, .error = GRPC_ERROR_NONE}),
+                       pack_received_status((received_status){
+                           .is_set = true, .error = error}))) {
     GRPC_ERROR_UNREF(error);
-    return;
   }
-  call->status[source].is_set = true;
-  call->status[source].error = error;
 }
 
 /*******************************************************************************