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

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Message-ID: <CANn89iJurbGWxN0Sbsh6XB7F6aYTmSPTa7LuaEDxVmCGs4wVgw@mail.gmail.com>
Date: Tue, 5 Nov 2024 19:26:22 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, 
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Simon Horman <horms@...nel.org>, 
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 net-next 1/2] ipv6: release nexthop on device removal

On Tue, Nov 5, 2024 at 7:24 PM Paolo Abeni <pabeni@...hat.com> 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@...f888013df15d8 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")
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>

Thanks a lot Paolo

Reviewed-by: Eric Dumazet <edumazet@...gle.com>