message: Make clean that the mu_ is dedicated for bias cache.
diff: @@ -1630,13 +1630,13 @@ class MklQuantizedConv2DOp
  }
  bool is_bias_const_;
  - PersistentTensor cached_bias_data_ptensor_ GUARDED_BY(mu_);
  + PersistentTensor cached_bias_data_ptensor_ GUARDED_BY(bias_cache_mu_);
  memory* input_bias_ = nullptr;
  memory* scaled_bias_ = nullptr;
  private:
  - mutex mu_;
  + mutex bias_cache_mu_;
  // Allocate persistent tensors for cached bias data and
  // cached bias memory descriptor (data format)
  void AllocatePersistentTensor(OpKernelContext* context,
  @@ -1654,8 +1654,8 @@ private:
  // LOCKS_EXCLUDED annotation ensures that the lock (mu_) cannot
  // be acquired before entering the function, since it is acquired
  // inside the function.
  - inline bool IsBiasCacheEmpty(OpKernelContext* context) LOCKS_EXCLUDED(mu_) {
  - tf_shared_lock lock(mu_);
  + inline bool IsBiasCacheEmpty(OpKernelContext* context) LOCKS_EXCLUDED(bias_cache_mu_) {
  + tf_shared_lock lock(bias_cache_mu_);
  return (cached_bias_data_ptensor_.NumElements() == 0);
  }
  @@ -1665,8 +1665,8 @@ private:
  const std::shared_ptr<ConvFwdPd>& conv_fwd_pd,
  Tbias *bias_data,
  const memory *scaled_bias)
  - LOCKS_EXCLUDED(mu_) {
  - mutex_lock lock(mu_);
  + LOCKS_EXCLUDED(bias_cache_mu_) {
  + mutex_lock lock(bias_cache_mu_);
  // If bias is already cached, there's nothing to do.
  if (cached_bias_data_ptensor_.NumElements() > 0) {
  @@ -1683,8 +1683,8 @@ private:
  }
  Tbias* GetCachedBias(OpKernelContext* context)
  - LOCKS_EXCLUDED(mu_) {
  - tf_shared_lock lock(mu_);
  + LOCKS_EXCLUDED(bias_cache_mu_) {
  + tf_shared_lock lock(bias_cache_mu_);
  const Tensor& cached_bias_data =
  *cached_bias_data_ptensor_.AccessTensor(context);
  