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Message-ID: <CADxym3Y2B+mcR6E_VYowE1VvCsa6X15RieOAr2nEofOswf_qfA@mail.gmail.com>
Date: Fri, 1 Aug 2025 18:42:33 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: kuniyu@...gle.com, kraig@...gle.com, ncardwell@...gle.com,
davem@...emloft.net, dsahern@...nel.org, kuba@...nel.org, pabeni@...hat.com,
horms@...nel.org, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net v2] net: ip: order the reuseport socket in __inet_hash
On Fri, Aug 1, 2025 at 5:46 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> On Fri, Aug 1, 2025 at 2:09 AM Menglong Dong <menglong8.dong@...il.com> wrote:
> >
> > For now, the socket lookup will terminate if the socket is reuse port in
> > inet_lhash2_lookup(), which makes the socket is not the best match.
> >
> > For example, we have socket1 and socket2 both listen on "0.0.0.0:1234",
> > but socket1 bind on "eth0". We create socket1 first, and then socket2.
> > Then, all connections will goto socket2, which is not expected, as socket1
> > has higher priority.
> >
> > This can cause unexpected behavior if TCP MD5 keys is used, as described
> > in Documentation/networking/vrf.rst -> Applications.
> >
> > Therefore, we compute a score for the reuseport socket and add it to the
> > list with order in __inet_hash(). Sockets with high score will be added
> > to the head.
> >
> > Link: https://lore.kernel.org/netdev/20250731123309.184496-1-dongml2@chinatelecom.cn/
> > Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
>
> You forgot a Fixes: tag, and a selftest.
I was not sure if it should be a Fixes, I'll add it in the next version.
Kuniyuki's test case is nice. Should I put the selftests in the
commit log?
>
> > ---
> > v2:
> > - As Kuniyuki advised, sort the reuseport socket in __inet_hash() to keep
> > the lookup for reuseport O(1)
>
> Keeping sorted the list is difficult, we would have to intercept
> SO_BINDTODEVICE, SO_BINDTOIFINDEX, SO_INCOMING_CPU.
>
> This also makes the patch risky to backport to stable versions,
> because it is complex and possibly buggy.
>
> Therefore I prefer your first approach.
Kuniyuki also has a similar patch:
https://lore.kernel.org/netdev/CADxym3ZY7Lm9mgv83e2db7o3ZZMcLDa=vDf6nJSs1m0_tUk5Bg@mail.gmail.com/T/#m56ee67b2fdf85ce568fd1339def92c53232d5b49
Will his be better and stable? Kuniyuki say the first approach
kill the O(1) lookup for reuseport socket :/
Anyway, I'll send a V3 with the first approach, and with
the Fixes + selftests
Thanks!
Menglong Dong
>
> > ---
> > include/linux/rculist_nulls.h | 34 ++++++++++++++++++++++++
> > include/net/sock.h | 5 ++++
> > net/ipv4/inet_hashtables.c | 49 ++++++++++++++++++++++++++++++++---
> > 3 files changed, 84 insertions(+), 4 deletions(-)
> >
> > diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
> > index 89186c499dd4..da500f4ae142 100644
> > --- a/include/linux/rculist_nulls.h
> > +++ b/include/linux/rculist_nulls.h
> > @@ -52,6 +52,13 @@ static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
> > #define hlist_nulls_next_rcu(node) \
> > (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
> >
> > +/**
> > + * hlist_nulls_pprev_rcu - returns the element of the list after @node.
> > + * @node: element of the list.
> > + */
> > +#define hlist_nulls_pprev_rcu(node) \
> > + (*((struct hlist_nulls_node __rcu __force **)&(node)->pprev))
> > +
> > /**
> > * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
> > * @n: the element to delete from the hash list.
> > @@ -145,6 +152,33 @@ static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
> > }
> > }
> >
> > +/**
> > + * hlist_nulls_add_before_rcu
> > + * @n: the new element to add to the hash list.
> > + * @next: the existing element to add the new element before.
> > + *
> > + * Description:
> > + * Adds the specified element to the specified hlist
> > + * before the specified node while permitting racing traversals.
> > + *
> > + * The caller must take whatever precautions are necessary
> > + * (such as holding appropriate locks) to avoid racing
> > + * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
> > + * or hlist_nulls_del_rcu(), running on this same list.
> > + * However, it is perfectly legal to run concurrently with
> > + * the _rcu list-traversal primitives, such as
> > + * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
> > + * problems on Alpha CPUs.
> > + */
> > +static inline void hlist_nulls_add_before_rcu(struct hlist_nulls_node *n,
> > + struct hlist_nulls_node *next)
> > +{
> > + WRITE_ONCE(n->pprev, next->pprev);
> I do not think WRITE_ONCE() is necessary here, @n is private to this cpu,
> and following rcu_assign_pointer() has the needed barrier.
>
> > + n->next = next;
> > + rcu_assign_pointer(hlist_nulls_pprev_rcu(n), n);
> > + WRITE_ONCE(next->pprev, &n->next);
> > +}
> > +
> > /* after that hlist_nulls_del will work */
> > static inline void hlist_nulls_add_fake(struct hlist_nulls_node *n)
> > {
> > diff --git a/include/net/sock.h b/include/net/sock.h
> > index c8a4b283df6f..42aa1919eeee 100644
> > --- a/include/net/sock.h
> > +++ b/include/net/sock.h
> > @@ -885,6 +885,11 @@ static inline void __sk_nulls_add_node_tail_rcu(struct sock *sk, struct hlist_nu
> > hlist_nulls_add_tail_rcu(&sk->sk_nulls_node, list);
> > }
> >
> > +static inline void __sk_nulls_add_node_before_rcu(struct sock *sk, struct sock *next)
> > +{
> > + hlist_nulls_add_before_rcu(&sk->sk_nulls_node, &next->sk_nulls_node);
> > +}
> > +
> > static inline void sk_nulls_add_node_rcu(struct sock *sk, struct hlist_nulls_head *list)
> > {
> > sock_hold(sk);
> > diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c
> > index ceeeec9b7290..80d8bec41a58 100644
> > --- a/net/ipv4/inet_hashtables.c
> > +++ b/net/ipv4/inet_hashtables.c
> > @@ -334,6 +334,26 @@ static inline int compute_score(struct sock *sk, const struct net *net,
> > return score;
> > }
> >
> > +static inline int compute_reuseport_score(struct sock *sk)
> > +{
> > + int score = 0;
> > +
> > + if (sk->sk_bound_dev_if)
> > + score += 2;
> > +
> > + if (sk->sk_family == PF_INET)
> > + score += 10;
> > +
> > + /* the priority of sk_incoming_cpu should be lower than sk_bound_dev_if,
> > + * as it's optional in compute_score(). Thank God, this is the only
>
> Please do not bring God here.
>
> > + * variable condition, which we can't judge now.
> > + */
> > + if (READ_ONCE(sk->sk_incoming_cpu))
> > + score++;
> > +
> > + return score;
> > +}
> > +
> > /**
> > * inet_lookup_reuseport() - execute reuseport logic on AF_INET socket if necessary.
> > * @net: network namespace.
> > @@ -739,6 +759,27 @@ static int inet_reuseport_add_sock(struct sock *sk,
> > return reuseport_alloc(sk, inet_rcv_saddr_any(sk));
> > }
> >
> > +static void inet_hash_reuseport(struct sock *sk, struct hlist_nulls_head *head)
> > +{
> > + const struct hlist_nulls_node *node;
> > + int score, curscore;
> > + struct sock *sk2;
> > +
> > + curscore = compute_reuseport_score(sk);
> > + /* lookup the socket to insert before */
> > + sk_nulls_for_each_rcu(sk2, node, head) {
> > + if (!sk2->sk_reuseport)
> > + continue;
> > + score = compute_reuseport_score(sk2);
> > + if (score <= curscore) {
> > + __sk_nulls_add_node_before_rcu(sk, sk2);
> > + return;
> > + }
> > + }
> > +
> > + __sk_nulls_add_node_tail_rcu(sk, head);
> > +}
> > +
> > int __inet_hash(struct sock *sk, struct sock *osk)
> > {
> > struct inet_hashinfo *hashinfo = tcp_get_hashinfo(sk);
> > @@ -761,11 +802,11 @@ int __inet_hash(struct sock *sk, struct sock *osk)
> > goto unlock;
> > }
> > sock_set_flag(sk, SOCK_RCU_FREE);
> > - if (IS_ENABLED(CONFIG_IPV6) && sk->sk_reuseport &&
> > - sk->sk_family == AF_INET6)
> > - __sk_nulls_add_node_tail_rcu(sk, &ilb2->nulls_head);
> > - else
> > + if (!sk->sk_reuseport)
> > __sk_nulls_add_node_rcu(sk, &ilb2->nulls_head);
> > + else
> > + inet_hash_reuseport(sk, &ilb2->nulls_head);
> > +
> > sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
> > unlock:
> > spin_unlock(&ilb2->lock);
> > --
> > 2.50.1
> >
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