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 --- v2: avoid list_empty() check as unregister_netdevice_many() already does it for us (Kuniyuki) --- drivers/net/ipvlan/ipvlan_main.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/net/ipvlan/ipvlan_main.c b/drivers/net/ipvlan/ipvlan_main.c index ee46a55f73d1..2d4340627ca6 100644 --- a/drivers/net/ipvlan/ipvlan_main.c +++ b/drivers/net/ipvlan/ipvlan_main.c @@ -846,7 +846,6 @@ static int ipvlan_device_event(struct notifier_block *unused, __ipvlan_link_delete(net, ipvlan->dev, &lst_kill); } - unregister_netdevice_many(&lst_kill); break; } case NETDEV_FEAT_CHANGE: @@ -895,6 +894,9 @@ static int ipvlan_device_event(struct notifier_block *unused, mutex_unlock(&port->pnodes_lock); + /* Avoid invoking nested netdevice notifiers under pnodes_lock. */ + unregister_netdevice_many(&lst_kill); + ipvlan_port_put(port); return ret; -- 2.43.0