Re: [PATCH] inet: fix fast path in __inet_hash_connect()

[Kuniyuki Iwashima <kuniyu@amazon.com>]

From:   Pietro Borrello <borrello@diag.uniroma1.it>
Date:   Thu, 12 Jan 2023 15:39:23 +0000
> __inet_hash_connect() has a fast path taken if sk_head(&tb->owners) is
> equal to the sk parameter.
> sk_head() returns the list_entry() with respect to the sk_node field.

nit: s/list_entry/hlist_entry/

> 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")
> Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>

Good catch!
Other than the nit above, looks good to me.

Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>

Thank you.


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