netdev - Re: [RFC PATCH 4/4] inet: use second hash in inet_csk_get

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Date:	Wed, 30 May 2012 22:11:02 +0300
From:	Alexandru Copot <alex.mihai.c@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	davem@...emloft.net, gerrit@....abdn.ac.uk, kuznet@....inr.ac.ru,
	jmorris@...ei.org, yoshfuji@...ux-ipv6.org, kaber@...sh.net,
	netdev@...r.kernel.org, Daniel Baluta <dbaluta@...acom.com>,
	Lucian Grijincu <lucian.grijincu@...il.com>
Subject: Re: [RFC PATCH 4/4] inet: use second hash in inet_csk_get_port

On Wed, May 30, 2012 at 8:20 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Wed, 2012-05-30 at 10:36 +0300, Alexandru Copot wrote:
>
>> +struct inet_bind_bucket *
>> +inet4_find_bind_buckets(struct sock *sk,
>> +                     unsigned short port,
>> +                     struct inet_bind_hashbucket **p_bhead,
>> +                     struct inet_bind_hashbucket **p_portaddr_bhead)
>> +{
>> +     struct net *net = sock_net(sk);
>> +     struct inet_hashinfo *hinfo = sk->sk_prot->h.hashinfo;
>> +     struct inet_bind_bucket *tb = NULL;
>> +     struct hlist_node *node;
>> +
>> +     struct inet_bind_hashbucket *bhead, *portaddr_bhead, *portaddrany_bhead;
>> +     bhead = &hinfo->bhash[inet_bhashfn(net, port, hinfo->bhash_size)];
>> +     portaddr_bhead = inet4_portaddr_hashbucket(hinfo, net,
>> +                             sk_rcv_saddr(sk), port);
>> +     portaddrany_bhead = inet4_portaddr_hashbucket(hinfo, net,
>> +                                             INADDR_ANY, port);
>> +
>> +     *p_portaddr_bhead = portaddr_bhead;
>> +     *p_bhead = bhead;
>> +
>> +     /*
>> +      * prevent dead locks by always taking locks in a fixed order:
>> +      * - always take the port-only lock first. This is done because in some
>> +      *   other places this is the lock taken, being folllowed in only some
>> +      *   cases by the portaddr lock.
>> +      * - between portaddr and portaddrany always choose the one with the
>> +      *   lower address. Unlock ordering is not important, as long as the
>> +      *   locking order is consistent.
>> +      * - make sure to not take the same lock twice
>> +      */
>> +     spin_lock(&bhead->lock);
>> +     if (portaddr_bhead > portaddrany_bhead) {
>> +             spin_lock(&portaddrany_bhead->lock);
>> +             spin_lock(&portaddr_bhead->lock);
>> +     } else if (portaddr_bhead < portaddrany_bhead) {
>> +             spin_lock(&portaddr_bhead->lock);
>> +             spin_lock(&portaddrany_bhead->lock);
>> +     } else {
>> +             spin_lock(&portaddr_bhead->lock);
>> +     }
>> +
>> +     if (sk_rcv_saddr(sk) != INADDR_ANY) {
>> +             struct inet_bind_hashbucket *_head;
>> +
>> +             _head = portaddr_bhead;
>> +             if (bhead->count < portaddr_bhead->count) {
>> +                     _head = bhead;
>> +                     inet_bind_bucket_for_each(tb, node, &_head->chain)
>> +                             if ((net_eq(ib_net(tb), net)) &&
>> +                                 (tb->port == port) &&
>> +                                 (tb->ib_addr_ipv4 == sk_rcv_saddr(sk)))
>> +                                     goto found;
>> +             } else {
>> +                     inet_portaddr_bind_bucket_for_each(tb, node, &_head->chain)
>> +                             if ((net_eq(ib_net(tb), net)) &&
>> +                                 (tb->port == port) &&
>> +                                 (tb->ib_addr_ipv4 == sk_rcv_saddr(sk)))
>> +                                     goto found;
>> +             }
>> +             _head = portaddrany_bhead;
>> +             if (bhead->count < portaddrany_bhead->count) {
>> +                     _head = bhead;
>> +                     inet_bind_bucket_for_each(tb, node, &_head->chain)
>> +                             if ((ib_net(tb) == net) &&
>> +                                 (tb->port == port) &&
>> +                                 (tb->ib_addr_ipv4 == INADDR_ANY))
>> +                                     goto found;
>> +             } else {
>> +                     inet_portaddr_bind_bucket_for_each(tb, node, &_head->chain)
>> +                             if ((ib_net(tb) == net) &&
>> +                                 (tb->port == port) &&
>> +                                 (tb->ib_addr_ipv4 == INADDR_ANY))
>> +                                     goto found;
>> +             }
>> +     } else {
>> +             inet_bind_bucket_for_each(tb, node, &bhead->chain)
>> +                     if ((ib_net(tb) == net) && (tb->port == port))
>> +                             goto found;
>> +     }
>> +
>> +     tb = NULL;
>> +found:
>> +     if (portaddr_bhead != portaddrany_bhead)
>> +             spin_unlock(&portaddrany_bhead->lock);
>> +
>> +     /* the other locks remain taken, as the caller
>> +      * may want to change the hash tabels */
>> +     return tb;
>> +}
>> +
>> +
>
> How this is going to work with IPv6 sockets in the middle of the
> chains ?

Now I see it might not work that well. I think I should just skip them
here and only check the IPv4 sockets.

> Also, comments are not properly formatted, they should all look like :
>
>        /* the other locks remain taken, as the caller
>         * may want to change the hash tables
>         */
>
> And finally, make sure LOCKDEP is happy with your locking code.
>
I will check that too.
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