Re: [PATCH v2 net-next 1/2] ipv6: release nexthop on device removal

[David Ahern <dsahern@kernel.org>]

On 11/5/24 11:23 AM, Paolo Abeni wrote:
> The CI is hitting some aperiodic hangup at device removal time in the
> pmtu.sh self-test:
> 
> unregister_netdevice: waiting for veth_A-R1 to become free. Usage count = 6
> ref_tracker: veth_A-R1@ffff888013df15d8 has 1/5 users at
> 	dst_init+0x84/0x4a0
> 	dst_alloc+0x97/0x150
> 	ip6_dst_alloc+0x23/0x90
> 	ip6_rt_pcpu_alloc+0x1e6/0x520
> 	ip6_pol_route+0x56f/0x840
> 	fib6_rule_lookup+0x334/0x630
> 	ip6_route_output_flags+0x259/0x480
> 	ip6_dst_lookup_tail.constprop.0+0x5c2/0x940
> 	ip6_dst_lookup_flow+0x88/0x190
> 	udp_tunnel6_dst_lookup+0x2a7/0x4c0
> 	vxlan_xmit_one+0xbde/0x4a50 [vxlan]
> 	vxlan_xmit+0x9ad/0xf20 [vxlan]
> 	dev_hard_start_xmit+0x10e/0x360
> 	__dev_queue_xmit+0xf95/0x18c0
> 	arp_solicit+0x4a2/0xe00
> 	neigh_probe+0xaa/0xf0
> 
> While the first suspect is the dst_cache, explicitly tracking the dst
> owing the last device reference via probes proved such dst is held by
> the nexthop in the originating fib6_info.
> 
> Similar to commit f5b51fe804ec ("ipv6: route: purge exception on
> removal"), we need to explicitly release the originating fib info when
> disconnecting a to-be-removed device from a live ipv6 dst: move the
> fib6_info cleanup into ip6_dst_ifdown().
> 
> Tested running:
> 
> ./pmtu.sh cleanup_ipv6_exception
> 
> in a tight loop for more than 400 iterations with no spat, running an
> unpatched kernel  I observed a splat every ~10 iterations.
> 
> Fixes: f88d8ea67fbd ("ipv6: Plumb support for nexthop object in a fib6_info")

are you sure that is the correct Fixes? That commit is June 2019 and
there have been stable periods since then without netdev release problems.

> Signed-off-by: Paolo Abeni <pabeni@redhat.com>
> ---
> v1 -> v2:
>  - dropped unintended whitespace change
> ---
>  net/ipv6/route.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 

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