message: Hold variable->mu() before PrepareToUpdateVariable.
diff: @@ -305,6 +305,7 @@ class StridedSliceAssignOp : public OpKernel {
  Var* v;
  OP_REQUIRES_OK(context,
  LookupResource(context, HandleFromInput(context, 0), &v));
  + mutex_lock ml(*v->mu());
  OP_REQUIRES_OK(context,
  PrepareToUpdateVariable<Device, T>(context, v->tensor()));
  old_lhs = *v->tensor();
  