On Tue, Oct 24, 2017 at 10:42:57AM +0000, Paolo Abeni wrote:
> Currently, the dst 'lastuse' field is not updated in a reliable way
> for dst entries only accessed via socket cache.
>
> This may fool the ipv6 dst gc, especially since we really age out unused
> entries, either via the commit 1859bac04fb6 ("ipv6: remove from fib tree
> aged out RTF_CACHE dst") or via the commit 1e2ea8ad37be ("ipv6: set
> dst.obsolete when a cached route has expired").
There is already an exception table and it already has a different way
of purging which is more inline with IPv4. It purges based on
'When was the last time the ICMPv6 too-big/redirect received' and
we purge the one that will expire sooner.
As we are moving away from the IPv6's gc,
I don't think we need to further depend on lastuse to purge/age
the RTF_CACHE on top of the purging being done in the exception
table.
Beside, lastuse is only useful for RTF_CACHE route (redirect
route in particular since it has no expire which we should give
it one imo). However, rt6_check() is called for everything,
e.g. non RTF_CACHE route which is the common case. Even though
dst_use_noref() is cheap to do now, it is still unnecessary for
the common fast path.
>
> Updating such field is now very cheap, thanks to commit 0da4af00b2ed
> ("ipv6: only update __use and lastusetime once per jiffy at most"),
> so we can address the issue updating 'lastuse' in ip6_dst_check(),
> if successful.
>
> Fixes: 1859bac04fb6 ("ipv6: remove from fib tree aged out RTF_CACHE dst")
> Fixes: 1e2ea8ad37be ("ipv6: set dst.obsolete when a cached route has expired")
> Signed-off-by: Paolo Abeni <[email protected]>
> ---
> net/ipv6/route.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 87a15cbd0e8b..8f8c7fb83b9b 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1952,6 +1952,7 @@ static struct dst_entry *rt6_check(struct rt6_info *rt,
> u32 cookie)
> if (rt6_check_expired(rt))
> return NULL;
>
> + dst_use_noref(&rt->dst, jiffies);
> return &rt->dst;
> }
>
> --
> 2.13.6
>
