Proactive Flushes: WBM::ShouldInitiateAnotherFlushMemOnly may return incorrect result due to a race

[udi-speedb]

This method calculates the difference between 2 atomic variables:

  bool ShouldInitiateAnotherFlushMemOnly(size_t curr_memory_used) const {
    return (curr_memory_used - memory_being_freed_ >=
                additional_flush_step_size_ / 2 &&
            curr_memory_used >= additional_flush_initiation_size_);
  }

However, the code decreases curr_memory_used and then memory_beingfreed. Therefore it may happen that the difference will overflow (rather than being negative) and the method will return true rather than false.