On 11/5/24 22:40, David Ahern wrote:
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.
"Sure" is a big word ;) AFAICS the mentioned commit let fib6_info store indirectly the extra dev reference via nexthop and does not clean it at device removal time.
Note that the issue is not deterministic - I needed ~30 mptu.sh iterations in a row to see it, so it could go unnoticed for a long time.
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
Thanks!
Paolo