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Currently, vxcan_dellink() unregisters both local and peer devices
synchronously under RTNL.
Once RTNL is removed, it can be called concurrently from different
netns.
Let's use xchg() and unregister_netdevice_queue_net() to support
per-netns device unregistration.
This way, each device is queued for destruction only once by
the winner of the race.
Note that the extra netdev_hold() ensures that @peer obtained by
the first xchg() is not freed during the subsequent access to
netdev_priv(peer). The 2nd xchg() overwrites @dev to balance
the refcount.
Tested:
1. Create two vxcan pairs (vxcan1-2, vxcan3-4) between two netns
(ns1 & ns2).
# ip netns add ns1
# ip netns add ns2
# ip -n ns1 link add vxcan1 type vxcan peer vxcan2 netns ns2
# ip -n ns1 link add vxcan3 type vxcan peer vxcan4 netns ns2
2. Run bpftrace to check if the same process does NOT
unregister the paired vxcan devices
# bpftrace -e '#include <linux/netdevice.h>
kprobe:free_netdev {
$dev = (struct net_device *)arg0;
printf("PID: %d | DEV: %s%s\n", pid, $dev->name, kstack());
}'
3. Remove vxcan2 in ns2 and check bpftrace output
# ip -n ns2 link del vxcan2
PID: 1524 | DEV: vxcan2
free_netdev+5
netdev_run_todo+4798
rtnl_dellink+1507
rtnetlink_rcv_msg+1791
netlink_rcv_skb+504
...
PID: 453 | DEV: vxcan1
free_netdev+5
netdev_run_todo+4798
process_scheduled_works+2538
worker_thread+1906
kthread+806
ret_from_fork+805
ret_from_fork_asm+17
4. Remove ns2 (thus vxcan4) and check bpftrace output
# ip netns del ns2
PID: 12 | DEV: vxcan4
free_netdev+5
netdev_run_todo+4798
default_device_exit_batch+2271
ops_undo_list+993
cleanup_net+1122
process_scheduled_works+2538
worker_thread+1906
kthread+806
ret_from_fork+805
ret_from_fork_asm+17
...
PID: 462 | DEV: vxcan3
free_netdev+5
netdev_run_todo+4798
process_scheduled_works+2538
worker_thread+1906
kthread+806
ret_from_fork+805
ret_from_fork_asm+17
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260731231755.2474376-1-kuniyu@google.com
[mkl: fix indention struct vxcan_priv::peer_tracker]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
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