netdev - Re: [PATCH net-next v3] inet: fix fast path in __inet_hash

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Date:   Tue, 17 Jan 2023 11:27:18 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Pietro Borrello <borrello@...g.uniroma1.it>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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>,
        Kuniyuki Iwashima <kuniyu@...zon.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3] inet: fix fast path in __inet_hash_connect()

On Tue, Jan 17, 2023 at 11:21 AM Paolo Abeni <pabeni@...hat.com> wrote:
>
> 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.
> >
> > 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.
> >
> > Signed-off-by: Pietro Borrello <borrello@...g.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_head-v2-1-5ec926ddd985@diag.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
> > ---
> >  net/ipv4/inet_hashtables.c | 12 +-----------
> >  1 file changed, 1 insertion(+), 11 deletions(-)
> >
> > 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_row *death_row,
> >       u32 index;
> >
> >       if (port) {
> > -             head = &hinfo->bhash[inet_bhashfn(net, port,
> > -                                               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) {
> > -                     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 = check_established(death_row, sk, port, NULL);
> >               local_bh_enable();
> >               return ret;
>
> LGTM, thanks!
>
> Eric, do you have any additional comment?

Oh right, I have missed this version.

Reviewed-by: Eric Dumazet <edumazet@...gle.com>

Thanks !