netdev - Re: [PATCH net-next v3 2/2] ipv6: remove from fib tree aged out RTF

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Date:   Thu, 19 Oct 2017 13:19:18 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH net-next v3 2/2] ipv6: remove from fib tree aged out
 RTF_CACHE dst

On Thu, Oct 19, 2017 at 7:07 AM, Paolo Abeni <pabeni@...hat.com> wrote:
> The commit 2b760fcf5cfb ("ipv6: hook up exception table to store
> dst cache") partially reverted the commit 1e2ea8ad37be ("ipv6: set
> dst.obsolete when a cached route has expired").
>
> As a result, RTF_CACHE dst referenced outside the fib tree will
> not be removed until the next sernum change; dst_check() does not
> fail on aged-out dst, and dst->__refcnt can't decrease: the aged
> out dst will stay valid for a potentially unlimited time after the
> timeout expiration.
>
> This change explicitly removes RTF_CACHE dst from the fib tree when
> aged out. The rt6_remove_exception() logic will then obsolete the
> dst and other entities will drop the related reference on next
> dst_check().
>
> pMTU exceptions are not aged-out, and are removed from the exception
> table only when the - usually considerably longer - ip6_rt_mtu_expires
> timeout expires.
>
> v1 -> v2:
>   - do not touch dst.obsolete in rt6_remove_exception(), not needed
> v2 -> v3:
>   - take care of pMTU exceptions, too
>
> Fixes: 2b760fcf5cfb ("ipv6: hook up exception table to store dst cache")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---

Acked-by: Wei Wang <weiwan@...gle.com>


>  net/ipv6/route.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 5c27313803d2..87a15cbd0e8b 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1575,7 +1575,13 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
>  {
>         struct rt6_info *rt = rt6_ex->rt6i;
>
> -       if (atomic_read(&rt->dst.__refcnt) == 1 &&
> +       /* we are pruning and obsoleting aged-out and non gateway exceptions
> +        * even if others have still references to them, so that on next
> +        * dst_check() such references can be dropped.
> +        * EXPIRES exceptions - e.g. pmtu-generated ones are pruned when
> +        * expired, independently from their aging, as per RFC 8201 section 4
> +        */
> +       if (!(rt->rt6i_flags & RTF_EXPIRES) &&
>             time_after_eq(now, rt->dst.lastuse + gc_args->timeout)) {
>                 RT6_TRACE("aging clone %p\n", rt);
>                 rt6_remove_exception(bucket, rt6_ex);
> @@ -1595,6 +1601,10 @@ static void rt6_age_examine_exception(struct rt6_exception_bucket *bucket,
>                         rt6_remove_exception(bucket, rt6_ex);
>                         return;
>                 }
> +       } else if (__rt6_check_expired(rt)) {
> +               RT6_TRACE("purging expired route %p\n", rt);
> +               rt6_remove_exception(bucket, rt6_ex);
> +               return;
>         }
>         gc_args->more++;
>  }
> --
> 2.13.6
>