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a8455260b2
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: 35add1093e ("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>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260828164918.451364-1-maciej.fijalkowski@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>