Re: [PATCH v6 net 3/3] selftest: net: Add GC test for temporary routes with exceptions.

[David Ahern <dsahern@kernel.org>]

On 3/20/26 1:23 AM, Kuniyuki Iwashima wrote:
> Without the prior commit, IPv6 GC cannot track exceptions tied
> to permanent routes if they were originally added as temporary
> routes.
> 
> Let's add a test case for the issue.
> 
>   1. Add temporary routes
>   2. Create exceptions for the temporary routes
>   3. Promote the routes to permanent routes
>   4. Check if GC can find and purge the exceptions
> 
> A few notes:
> 
>   + At step 4, unlike other test cases, we cannot wait for
>     $GC_WAIT_TIME.  While the exceptions are always iterable via
>     netlink (since it traverses the entire fib tree instead of
>     tb6_gc_hlist), rt6_nh_dump_exceptions() skips expired entries.
> 
>     If we waited for the expiration time, we would be unable to
>     distinguish whether the exceptions were truly purged by GC or
>     just hidden due to being expired.
> 
>   + For the same reason, at step 2, we use ICMPv6 redirect message
>     instead of Packet Too Big message.  This is because MTU exceptions
>     always have RTF_EXPIRES, and rt6_age_examine_exception() does not
>     respect the period specified by net.ipv6.route.flush=1.
> 
>   + We add a neighbour entry for the redirect target with NTF_ROUTER.
>     Without this, the exceptions would be removed at step 3 when the
>     fib6_may_remove_gc_list() is called.
> 
> Without the fix, the exceptions remain even after GC is triggered
> by sysctl -wq net.ipv6.route.flush=1.
> 
>   FAIL: Expected 0 routes, got 5
>       TEST: ipv6 route garbage collection (promote to permanent routes)   [FAIL]
> 
> With the fix, GC purges the exceptions properly.
> 
>       TEST: ipv6 route garbage collection (promote to permanent routes)   [ OK ]
> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---
>  tools/testing/selftests/net/fib_tests.sh | 61 ++++++++++++++++++++++--
>  1 file changed, 58 insertions(+), 3 deletions(-)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>