============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/u8:4/5885 is trying to acquire lock:
ffff88816b967d58 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0

but task is already holding lock:
ffff8881122d3558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0

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

       CPU0
       ----
  lock(&qdisc_xmit_lock_key#4);
  lock(&qdisc_xmit_lock_key#4);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

15 locks held by kworker/u8:4/5885:
 #0: ffff88817140e948 ((wq_completion)ipv6_addrconf){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0
 #1: ffffc90004c57ba0 ((work_completion)(&(&ifa->dad_work)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0
 #2: ffffffff8f2cb1c8 (rtnl_mutex){+.+.}-{4:4}, at: addrconf_dad_work+0x112/0x14b0
 #3: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: ndisc_send_skb+0x1e4/0x1510
 #4: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: ip6_output+0x126/0x550
 #5: ffffffff8df3d340 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x284/0x3740
 #6: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: bond_start_xmit+0xf8/0x1a10
 #7: ffffffff8df3d340 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x284/0x3740
 #8: ffff8881bada91e8 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x11e2/0x3740
 #9: ffff8881122d3558 (&qdisc_xmit_lock_key#4){+.-.}-{3:3}, at: sch_direct_xmit+0x153/0x4b0
 #10: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: ip_output+0x5b/0x450
 #11: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: ip_finish_output2+0x452/0x1160
 #12: ffffffff8df3d2e0 (rcu_read_lock){....}-{1:3}, at: arp_xmit+0x23/0x270
 #13: ffffffff8df3d340 (rcu_read_lock_bh){....}-{1:3}, at: __dev_queue_xmit+0x284/0x3740
 #14: ffff8881a9d481e8 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock#3){+...}-{3:3}, at: __dev_queue_xmit+0x11e2/0x3740

stack backtrace:
CPU: 1 UID: 0 PID: 5885 Comm: kworker/u8:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: ipv6_addrconf addrconf_dad_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_deadlock_bug+0x28b/0x2a0
 validate_chain+0x1a3f/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 _raw_spin_lock+0x2e/0x40
 sch_direct_xmit+0x153/0x4b0
 __dev_queue_xmit+0x1619/0x3740
 NF_HOOK+0x310/0x3a0
 arp_xmit+0x16c/0x270
 arp_solicit+0xc1d/0xe60
 __neigh_event_send+0xf70/0x1560
 neigh_resolve_output+0x198/0x750
 ip_finish_output2+0xd40/0x1160
 ip_output+0x29f/0x450
 iptunnel_xmit+0x5f8/0xa90
 ip_tunnel_xmit+0x1c41/0x2390
 gre_tap_xmit+0x590/0x7a0
 dev_hard_start_xmit+0x2d7/0x830
 sch_direct_xmit+0x241/0x4b0
 __dev_queue_xmit+0x1619/0x3740
 bond_dev_queue_xmit+0x10b/0x1e0
 bond_start_xmit+0x779/0x1a10
 dev_hard_start_xmit+0x2d7/0x830
 __dev_queue_xmit+0x172a/0x3740
 ip6_finish_output2+0xfb3/0x1480
 ip6_output+0x340/0x550
 ndisc_send_skb+0xbce/0x1510
 ndisc_send_ns+0xcb/0x150
 addrconf_dad_work+0xaae/0x14b0
 process_scheduled_works+0xae1/0x17b0
 worker_thread+0x8a0/0xda0
 kthread+0x711/0x8a0
 ret_from_fork+0x4bc/0x870
 ret_from_fork_asm+0x1a/0x30
 </TASK>
