udp_tunnel: fix deadlock in udp_tunnel_nic_set_port_priv()

While configuring a vxlan tunnel in a system with a i40e NIC driver, I
observe the following deadlock:

 WARNING: possible recursive locking detected
 6.16.0-rc2.net-next-6.16_92d87230d899+ torvalds#13 Tainted: G            E
 --------------------------------------------
 kworker/u256:4/1125 is trying to acquire lock:
 ffff88921ab9c8c8 (&utn->lock){+.+.}-{4:4}, at: i40e_udp_tunnel_set_port (/home/pabeni/net-next/include/net/udp_tunnel.h:343 /home/pabeni/net-next/drivers/net/ethernet/intel/i40e/i40e_main.c:13013) i40e

 but task is already holding lock:
 ffff88921ab9c8c8 (&utn->lock){+.+.}-{4:4}, at: udp_tunnel_nic_device_sync_work (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:739) udp_tunnel

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(&utn->lock);
   lock(&utn->lock);

  *** DEADLOCK ***

  May be due to missing lock nesting notation

 4 locks held by kworker/u256:4/1125:
 #0: ffff8892910ca158 ((wq_completion)udp_tunnel_nic){+.+.}-{0:0}, at: process_one_work (/home/pabeni/net-next/kernel/workqueue.c:3213)
 #1: ffffc900244efd30 ((work_completion)(&utn->work)){+.+.}-{0:0}, at: process_one_work (/home/pabeni/net-next/kernel/workqueue.c:3214)
 #2: ffffffff9a14e290 (rtnl_mutex){+.+.}-{4:4}, at: udp_tunnel_nic_device_sync_work (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:737) udp_tunnel
 #3: ffff88921ab9c8c8 (&utn->lock){+.+.}-{4:4}, at: udp_tunnel_nic_device_sync_work (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:739) udp_tunnel

 stack backtrace:
 Hardware name: Dell Inc. PowerEdge R7525/0YHMCJ, BIOS 2.2.5 04/08/2021
i
 Call Trace:
  <TASK>
 dump_stack_lvl (/home/pabeni/net-next/lib/dump_stack.c:123)
 print_deadlock_bug (/home/pabeni/net-next/kernel/locking/lockdep.c:3047)
 validate_chain (/home/pabeni/net-next/kernel/locking/lockdep.c:3901)
 __lock_acquire (/home/pabeni/net-next/kernel/locking/lockdep.c:5240)
 lock_acquire.part.0 (/home/pabeni/net-next/kernel/locking/lockdep.c:473 /home/pabeni/net-next/kernel/locking/lockdep.c:5873)
 __mutex_lock (/home/pabeni/net-next/kernel/locking/mutex.c:604 /home/pabeni/net-next/kernel/locking/mutex.c:747)
 i40e_udp_tunnel_set_port (/home/pabeni/net-next/include/net/udp_tunnel.h:343 /home/pabeni/net-next/drivers/net/ethernet/intel/i40e/i40e_main.c:13013) i40e
 udp_tunnel_nic_device_sync_by_port (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:230 /home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:249) udp_tunnel
 __udp_tunnel_nic_device_sync.part.0 (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:292) udp_tunnel
 udp_tunnel_nic_device_sync_work (/home/pabeni/net-next/net/ipv4/udp_tunnel_nic.c:742) udp_tunnel
 process_one_work (/home/pabeni/net-next/kernel/workqueue.c:3243)
 worker_thread (/home/pabeni/net-next/kernel/workqueue.c:3315 /home/pabeni/net-next/kernel/workqueue.c:3402)
 kthread (/home/pabeni/net-next/kernel/kthread.c:464)

AFAICS all the existing callsites of udp_tunnel_nic_set_port_priv() are
already under the utn lock scope, avoid (re-)acquiring it in such a
function.

Fixes: 1ead750 ("udp_tunnel: remove rtnl_lock dependency")
Signed-off-by: Paolo Abeni <[email protected]>
Signed-off-by: NipaLocal <nipa@local>

Author: Paolo Abeni

include/net/udp_tunnel.h

@@ -339,9 +339,8 @@ udp_tunnel_nic_set_port_priv(struct net_device *dev, unsigned int table,
 			     unsigned int idx, u8 priv)
 {
 	if (udp_tunnel_nic_ops) {
-		udp_tunnel_nic_ops->lock(dev);
+		udp_tunnel_nic_ops->assert_locked(dev);
 		udp_tunnel_nic_ops->set_port_priv(dev, table, idx, priv);
-		udp_tunnel_nic_ops->unlock(dev);
 	}
 }