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Message-ID: <cf3c7895be29d46e814d356bb5afad1203815253.camel@redhat.com>
Subject: Re: [PATCH net-next v3] inet: fix fast path in __inet_hash_connect()
From:   Paolo Abeni <pabeni@redhat.com>
To:     Pietro Borrello <borrello@diag.uniroma1.it>,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Jakub Kicinski <kuba@kernel.org>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>
Cc:     Cristiano Giuffrida <c.giuffrida@vu.nl>,
        "Bos, H.J." <h.j.bos@vu.nl>, Jakob Koschel <jkl820.git@gmail.com>,
        Kuniyuki Iwashima <kuniyu@amazon.com>, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Tue, 17 Jan 2023 11:21:39 +0100
In-Reply-To: <20230112-inet_hash_connect_bind_head-v3-1-b591fd212b93@diag.uniroma1.it>
References: <20230112-inet_hash_connect_bind_head-v3-1-b591fd212b93@diag.uniroma1.it>
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On Sat, 2023-01-14 at 13:11 +0000, Pietro Borrello 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.
>=20
> This fast path has never been executed or tested as this bug seems
> to be present since commit 1da177e4c3f4 ("Linux-2.6.12-rc2"), thus
> remove it to reduce code complexity.
>=20
> Signed-off-by: Pietro Borrello <borrello@diag.uniroma1.it>
> ---
> Changes in v3:
> - remove the fast path to reduce code complexity
> - Link to v2: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_h=
ead-v2-1-5ec926ddd985@diag.uniroma1.it
>=20
> Changes in v2:
> - nit: s/list_entry/hlist_entry/
> - Link to v1: https://lore.kernel.org/r/20230112-inet_hash_connect_bind_h=
ead-v1-1-7e3c770157c8@diag.uniroma1.it
> ---
>  net/ipv4/inet_hashtables.c | 12 +-----------
>  1 file changed, 1 insertion(+), 11 deletions(-)
>=20
> diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> index d039b4e732a3..b832e7a545d4 100644
> --- a/net/ipv4/inet_hashtables.c
> +++ b/net/ipv4/inet_hashtables.c
> @@ -994,17 +994,7 @@ int __inet_hash_connect(struct inet_timewait_death_r=
ow *death_row,
>  	u32 index;
> =20
>  	if (port) {
> -		head =3D &hinfo->bhash[inet_bhashfn(net, port,
> -						  hinfo->bhash_size)];
> -		tb =3D inet_csk(sk)->icsk_bind_hash;
> -		spin_lock_bh(&head->lock);
> -		if (sk_head(&tb->owners) =3D=3D sk && !sk->sk_bind_node.next) {
> -			inet_ehash_nolisten(sk, NULL, NULL);
> -			spin_unlock_bh(&head->lock);
> -			return 0;
> -		}
> -		spin_unlock(&head->lock);
> -		/* No definite answer... Walk to established hash table */
> +		local_bh_disable();
>  		ret =3D check_established(death_row, sk, port, NULL);
>  		local_bh_enable();
>  		return ret;

LGTM, thanks!

Eric, do you have any additional comment?

Cheers,

Paolo