netdev - Re: [PATCH v2] inet: fix fast path in __inet_hash

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Date:   Fri, 13 Jan 2023 13:16:20 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Pietro Borrello <borrello@...g.uniroma1.it>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Jakob Koschel <jkl820.git@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Kuniyuki Iwashima <kuniyu@...zon.com>
Subject: Re: [PATCH v2] inet: fix fast path in __inet_hash_connect()

On Fri, Jan 13, 2023 at 12:40 PM Pietro Borrello
<borrello@...g.uniroma1.it> wrote:
>
> __inet_hash_connect() has a fast path taken if sk_head(&tb->owners) is
> equal to the sk parameter.
> sk_head() returns the hlist_entry() with respect to the sk_node field.
> However entries in the tb->owners list are inserted with respect to the
> sk_bind_node field with sk_add_bind_node().
> Thus the check would never pass and the fast path never execute.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>
> Signed-off-by: Pietro Borrello <borrello@...g.uniroma1.it>
> ---
> Changes in v2:
> - nit: s/list_entry/hlist_entry/
> - Link to v1: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_head-v1-1-7e3c770157c8@diag.uniroma1.it
> ---
>  include/net/sock.h         | 10 ++++++++++
>  net/ipv4/inet_hashtables.c |  2 +-
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/include/net/sock.h b/include/net/sock.h
> index dcd72e6285b2..23fc403284db 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -860,6 +860,16 @@ static inline void sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_hea
>         __sk_nulls_add_node_rcu(sk, list);
>  }
>
> +static inline struct sock *__sk_bind_head(const struct hlist_head *head)
> +{
> +       return hlist_entry(head->first, struct sock, sk_bind_node);
> +}
> +
> +static inline struct sock *sk_bind_head(const struct hlist_head *head)
> +{
> +       return hlist_empty(head) ? NULL : __sk_bind_head(head);
> +}
> +
>  static inline void __sk_del_bind_node(struct sock *sk)
>  {
>         __hlist_del(&sk->sk_bind_node);
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index d039b4e732a3..a805e086fb48 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -998,7 +998,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row,
>                                                   hinfo->bhash_size)];
>                 tb = inet_csk(sk)->icsk_bind_hash;
>                 spin_lock_bh(&head->lock);
> -               if (sk_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
> +               if (sk_bind_head(&tb->owners) == sk && !sk->sk_bind_node.next) {
>                         inet_ehash_nolisten(sk, NULL, NULL);

1) Given this path was never really used, we have no coverage.

2) Given that we do not check inet_ehash_nolisten() return code here.

I would recommend _not_ adding the Fixes: tag, and target net-next tree

In fact, I would remove this dead code, and reduce complexity.

I doubt the difference is going to be noticed.
(We have to access the ehash bucket anyway)


>                         spin_unlock_bh(&head->lock);
>                         return 0;
>
> ---
> base-commit: 1b929c02afd37871d5afb9d498426f83432e71c2
> change-id: 20230112-inet_hash_connect_bind_head-8f2dc98f08b1
>
> Best regards,
> --
> Pietro Borrello <borrello@...g.uniroma1.it>