Re: [PATCH net-next 1/5] tcp: Create list of TFO-contexts

[Eric Dumazet <eric.dumazet@gmail.com>]

On 12/14/2018 02:40 PM, Christoph Paasch wrote:
> Instead of having a single TFO-context, we now have a list of
> tcp_fastopen_context, bounded by TCP_FASTOPEN_CTXT_LEN (set to 2).
> 
> This enables us to do a rolling TFO-key update that allows the server to
> accept old cookies and at the same time announce new ones to the client
> (see follow-up patch).
> 
> Signed-off-by: Christoph Paasch <cpaasch@apple.com>
> ---
>  include/net/tcp.h       |  2 ++
>  net/ipv4/tcp_fastopen.c | 52 +++++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 50 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index e0a65c067662..e629ea2e6c9d 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -1622,9 +1622,11 @@ bool tcp_fastopen_cookie_check(struct sock *sk, u16 *mss,
>  			     struct tcp_fastopen_cookie *cookie);
>  bool tcp_fastopen_defer_connect(struct sock *sk, int *err);
>  #define TCP_FASTOPEN_KEY_LENGTH 16
> +#define TCP_FASTOPEN_CTXT_LEN 2
>  
>  /* Fastopen key context */
>  struct tcp_fastopen_context {
> +	struct tcp_fastopen_context __rcu *next;
>  	struct crypto_cipher	*tfm;
>  	__u8			key[TCP_FASTOPEN_KEY_LENGTH];
>  	struct rcu_head		rcu;
> diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
> index 018a48477355..c52d5b8eabf0 100644
> --- a/net/ipv4/tcp_fastopen.c
> +++ b/net/ipv4/tcp_fastopen.c
> @@ -37,8 +37,14 @@ static void tcp_fastopen_ctx_free(struct rcu_head *head)
>  {
>  	struct tcp_fastopen_context *ctx =
>  	    container_of(head, struct tcp_fastopen_context, rcu);
> -	crypto_free_cipher(ctx->tfm);
> -	kfree(ctx);
> +
> +	while (ctx) {
> +		struct tcp_fastopen_context *prev = ctx;
> +		/* We own ctx, thus no need to hold the Fastopen-lock */
> +		ctx = rcu_dereference_protected(ctx->next, 1);
> +		crypto_free_cipher(prev->tfm);
> +		kfree(prev);
> +	}
>

It seems this function does not need to be changed, since at most one context
should be freed per run ?