can: vxcan: support per-netns device unregistration.

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>

0 files changed, 0 insertions, 0 deletions