Re: [PATCH net-next] tcp: add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb()

[Yunsheng Lin]

On 2021/9/1 18:39, Yunsheng Lin wrote:
> Since tcp_tx_skb_cache is disabled by default in:
> commit 0b7d7f6b2208 ("tcp: add tcp_tx_skb_cache sysctl")
> 
> Add tcp_tx_skb_cache_key checking in sk_stream_alloc_skb() to
> avoid possible branch-misses.
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
> ---
> Also, the sk->sk_tx_skb_cache may be both changed by allocation
> and freeing side, I assume there may be some implicit protection
> here too, such as the NAPI protection for rx?

Hi, Eric
   Is there any implicit protection for sk->sk_tx_skb_cache?
As my understanding, sk_stream_alloc_skb() seems to be protected
by lock_sock(), and the sk_wmem_free_skb() seems to be mostly
happening in NAPI polling for TCP(when ack packet is received)
without lock_sock(), so it seems there is no protection here?

>