Re: [PATCH v2 net] ipvlan: unregister upper devices outside pnodes_lock

On Fri, Aug 28, 2026 at 6:49 PM Maciej Fijalkowski
[off-list ref] wrote:

syzbot reported the following circular locking dependency:

  xs->mutex -> netdev lock -> pnodes_lock -> net->xdp.lock -> xs->mutex

The pnodes_lock -> net->xdp.lock edge is recorded when
ipvlan_device_event(NETDEV_UNREGISTER) calls unregister_netdevice_many()
while holding pnodes_lock.  A nested NETDEV_UNREGISTER notification for
an IPvlan device enters xsk_notifier(), which acquires net->xdp.lock.

Keep pnodes_lock only while marking the upper devices as dying, removing
them from port->ipvlans, and queueing them for unregistration.  Once the
devices have been detached from the protected list, release pnodes_lock
before unregister_netdevice_many() invokes notifier callbacks.

The port remains alive across unregistration because
ipvlan_device_event() holds the reference acquired by ipvlan_port_get().
The dying flag prevents a concurrent ->dellink() callback from deleting a
queued device again.

Fixes: 35add1093e2f ("ipvlan: Protect ipvl_port.ipvlans with mutex.")
Reported-by: syzbot+aa48b5fe7bfda62d1682@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=aa48b5fe7bfda62d1682
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

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