On Tue, Feb 15, 2022 at 3:30 AM <menglong8.dong@xxxxxxxxx> wrote:
>
> From: Menglong Dong <imagedong@xxxxxxxxxxx>
>
> For TCP protocol, tcp_drop() is used to free the skb when it needs
> to be dropped. To make use of kfree_skb_reason() and collect drop
> reasons, introduce the function tcp_drop_reason().
>
> tcp_drop_reason() will finally call kfree_skb_reason() and pass the
> drop reason to 'kfree_skb' tracepoint.
>
> PS: __kfree_skb() was used in tcp_drop(), I'm not sure if it's ok
> to replace it with kfree_skb_reason().
>
> Signed-off-by: Menglong Dong <imagedong@xxxxxxxxxxx>
> ---
> net/ipv4/tcp_input.c | 13 +++++++++++--
> 1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index af94a6d22a9d..e3811afd1756 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -4684,10 +4684,19 @@ static bool tcp_ooo_try_coalesce(struct sock *sk,
> return res;
> }
>
> -static void tcp_drop(struct sock *sk, struct sk_buff *skb)
> +static void tcp_drop_reason(struct sock *sk, struct sk_buff *skb,
> + enum skb_drop_reason reason)
> {
> sk_drops_add(sk, skb);
> - __kfree_skb(skb);
> + /* why __kfree_skb() used here before, other than kfree_skb()?
> + * confusing......
Do not add comments like that if you do not know the difference...
__kfree_skb() is used by TCP stack because it owns skb in receive
queues, and avoids touching skb->users
because it must be one already.
(We made sure not using skb_get() in TCP)
It seems fine to use kfree_skb() in tcp_drop(), it is hardly fast
path, and the added cost is pure noise.
