VRF/IPv4/ARP: unregister_netdevice waiting for dev to become free -> Who's responsible for releasing dst_entry created by ip_route_input_noref?

[Oliver Herms <oliver.peter.herms@gmail.com>]

Hi everyone,

I'm observing an device unregistration issue when I try to delete a VRF interface after using the VRF.
The issue is reproducible on 5.12.9, 5.10.24, 5.11.0-18 (debian).

Here are the steps to reproduce the issue:

ip addr add 10.0.0.1/32 dev lo
ip netns add test-ns
ip link add veth-outside type veth peer name veth-inside
ip link add vrf-100 type vrf table 1100
ip link set veth-outside master vrf-100
ip link set veth-inside netns test-ns
ip link set veth-outside up
ip link set vrf-100 up
ip route add 10.1.1.1/32 dev veth-outside table 1100
ip netns exec test-ns ip link set veth-inside up
ip netns exec test-ns ip addr add 10.1.1.1/32 dev veth-inside
ip netns exec test-ns ip route add 10.0.0.1/32 dev veth-inside
ip netns exec test-ns ip route add default via 10.0.0.1
ip netns exec test-ns ping 10.0.0.1 -c 1 -i 1
sleep 10
ip link set veth-outside nomaster
ip link set vrf-100 down
ip link delete vrf-100 <= Never returns

The issue does not happen when I don't do the ping.

I've tracked down all calls to dev_hold and dev_put.
When the ping command is run there is the following call to dev_hold to which the corresponding dev_put seems to be missing (doesn't even happen when the VRF is set down or deleted):
[  284.528775] CPU: 2 PID: 1205 Comm: ping Not tainted 5.12.9 #1
[  284.528790] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006
[  284.528796] Call Trace:
[  284.528802]  <IRQ>
[  284.528832]  dump_stack+0x7d/0x9c
[  284.528854]  dst_alloc.cold+0x11/0x2a
[  284.528866]  rt_dst_alloc+0x48/0xd0
[  284.528881]  ip_route_input_slow+0x507/0xc80
[  284.528900]  ip_route_input_rcu+0x258/0x270
[  284.528913]  ip_route_input_noref+0x2a/0x50
[  284.528923]  arp_process+0x4da/0x8a0
[  284.528938]  arp_rcv+0x1a9/0x1d0
[  284.528948]  ? trigger_load_balance+0x205/0x240
[  284.528961]  __netif_receive_skb_one_core+0x8d/0xa0
[  284.528974]  __netif_receive_skb+0x18/0x60
[  284.528984]  process_backlog+0xa2/0x170
[  284.528993]  __napi_poll+0x31/0x170
[  284.529002]  net_rx_action+0x22f/0x280
[  284.529012]  __do_softirq+0xce/0x281
[  284.529024]  do_softirq+0x77/0xa0
[  284.529049]  </IRQ>
[  284.529054]  __local_bh_enable_ip+0x50/0x60
[  284.529064]  ip_finish_output2+0x1ab/0x590
[  284.529073]  ? __cgroup_bpf_run_filter_skb+0x3ce/0x3e0
[  284.529086]  __ip_finish_output+0x110/0x270
[  284.529096]  ip_finish_output+0x2d/0xb0
[  284.529105]  ip_output+0x78/0x100
[  284.529114]  ? __ip_finish_output+0x270/0x270
[  284.529122]  ip_push_pending_frames+0xa3/0xb0
[  284.529131]  raw_sendmsg+0x5f0/0xdb0
[  284.529144]  ? setup_min_slab_ratio+0x68/0x90
[  284.529182]  ? __cond_resched+0x1a/0x50
[  284.529195]  ? aa_sk_perm+0x43/0x1b0
[  284.529211]  inet_sendmsg+0x6c/0x70
[  284.529221]  sock_sendmsg+0x5e/0x70
[  284.529234]  __sys_sendto+0x113/0x190
[  284.529249]  ? handle_mm_fault+0xda/0x2c0
[  284.529258]  ? do_user_addr_fault+0x1f5/0x670
[  284.529266]  ? exit_to_user_mode_prepare+0x37/0x190
[  284.529277]  __x64_sys_sendto+0x29/0x30
[  284.529287]  do_syscall_64+0x38/0x90
[  284.529298]  entry_SYSCALL_64_after_hwframe+0x44/0xae
[  284.529306] RIP: 0033:0x7f89f02db53a
[  284.529317] Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 f3 0f 1e fa 41 89 ca 64 8b 04 25 18 00 00 00 85 c0 75 15 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 76 c3 0f 1f 44 00 00 55 48 83 ec 30 44 89 4c
[  284.529325] RSP: 002b:00007ffd7c1b0478 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
[  284.529335] RAX: ffffffffffffffda RBX: 00007ffd7c1b1c00 RCX: 00007f89f02db53a
[  284.529340] RDX: 0000000000000040 RSI: 00005592d86be100 RDI: 0000000000000003
[  284.529345] RBP: 00005592d86be100 R08: 00007ffd7c1b3e7c R09: 0000000000000010
[  284.529349] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000040
[  284.529354] R13: 00007ffd7c1b1bc0 R14: 00007ffd7c1b0480 R15: 0000001d00000001

Processing the incoming ARP request causes a call to ip_route_input_noref => ip_route_input_rcu => ip_route_input_slow => rt_dst_alloc => dst_alloc => dev_hold.
In a non VRF use-case the dst->dev would be the loopback interface that is never deleted. In the VRF use-case dst->dev is the VRF interface. And that one I would like to delete.

I've tracked down that dst_release() would call dev_put() but it seems dst_release is not called here (but should be I guess?). Thus, causing a dst_entry leak that causes the VRF device to be unremovable.
At least that's what it looks like to me.

So: Who's responsible for releasing dst_entry created by ip_route_input_noref in arp_process?

Kind Regards
Oliver