Query regarding a code snippet in __inet_lookup_established.

Query regarding a code snippet in __inet_lookup_established.

[MuraliRaja Muniraju]

Hi All,
    In function __inet_lookup_established, I do see a potential issue
in a corner case while reading through the code where socket can be
freed while being in the list and also while in rcu_read critical
section.
        rcu_read_lock();
begin:
        sk_nulls_for_each_rcu(sk, node, &head->chain) {
                if (INET_MATCH(sk, net, hash, acookie,
                                        saddr, daddr, ports, dif)) {
                        if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
                                goto begintw;
                        if (unlikely(!INET_MATCH(sk, net, hash, acookie,
                                saddr, daddr, ports, dif))) {
Murali>                                sock_put(sk);
Murali>                                goto begin;
                        }
                        goto out;
                }
        }

I am not certain under what scenario this might occur. Can someone let
me know if this is a possibility.
-- 
Thanks,
Murali

Re: Query regarding a code snippet in __inet_lookup_established.

[Eric Dumazet]

Le vendredi 20 janvier 2012 à 17:02 -0800, MuraliRaja Muniraju a écrit :
> Hi All,
>     In function __inet_lookup_established, I do see a potential issue
> in a corner case while reading through the code where socket can be
> freed while being in the list and also while in rcu_read critical
> section.
>         rcu_read_lock();
> begin:
>         sk_nulls_for_each_rcu(sk, node, &head->chain) {
>                 if (INET_MATCH(sk, net, hash, acookie,
>                                         saddr, daddr, ports, dif)) {
>                         if (unlikely(!atomic_inc_not_zero(&sk->sk_refcnt)))
>                                 goto begintw;
>                         if (unlikely(!INET_MATCH(sk, net, hash, acookie,
>                                 saddr, daddr, ports, dif))) {
> Murali>                                sock_put(sk);
> Murali>                                goto begin;
>                         }
>                         goto out;
>                 }
>         }
> 
> I am not certain under what scenario this might occur. Can someone let
> me know if this is a possibility.

Since we succeeded in atomic_inc_not_zero(&sk->sk_refcnt), socket cannot
be freed until our sock_put()