======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.6783/32686 is trying to acquire lock:
ffffffff8f425578 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_device_down+0xa9/0x720

but task is already holding lock:
ffffffff8f425518 (nr_neigh_list_lock){+.-.}-{3:3}, at: nr_rt_device_down+0x28/0x720

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_neigh_list_lock){+.-.}-{3:3}:
       lock_acquire+0x120/0x360
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_ioctl+0x390/0xd50
       sock_do_ioctl+0xdc/0x300
       sock_ioctl+0x576/0x790
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (&nr_node->node_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_ioctl+0x193/0xd50
       sock_do_ioctl+0xdc/0x300
       sock_ioctl+0x576/0x790
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_node_list_lock){+...}-{3:3}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       lock_acquire+0x120/0x360
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_device_down+0xa9/0x720
       nr_device_event+0x137/0x150
       notifier_call_chain+0x1b6/0x3e0
       __dev_notify_flags+0x18d/0x2e0
       netif_change_flags+0xe8/0x1a0
       dev_change_flags+0x130/0x260
       dev_ioctl+0x7b4/0x1150
       sock_do_ioctl+0x22c/0x300
       sock_ioctl+0x576/0x790
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0xfa/0xfa0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Chain exists of:
  nr_node_list_lock --> &nr_node->node_lock --> nr_neigh_list_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(nr_neigh_list_lock);
                               lock(&nr_node->node_lock);
                               lock(nr_neigh_list_lock);
  lock(nr_node_list_lock);

 *** DEADLOCK ***

2 locks held by syz.2.6783/32686:
 #0: ffffffff8f2cb208 (rtnl_mutex){+.+.}-{4:4}, at: dev_ioctl+0x7a4/0x1150
 #1: ffffffff8f425518 (nr_neigh_list_lock){+.-.}-{3:3}, at: nr_rt_device_down+0x28/0x720

stack backtrace:
CPU: 0 UID: 0 PID: 32686 Comm: syz.2.6783 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
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 print_circular_bug+0x2ee/0x310
 check_noncircular+0x134/0x160
 validate_chain+0xb9b/0x2140
 __lock_acquire+0xab9/0xd20
 lock_acquire+0x120/0x360
 _raw_spin_lock_bh+0x36/0x50
 nr_rt_device_down+0xa9/0x720
 nr_device_event+0x137/0x150
 notifier_call_chain+0x1b6/0x3e0
 __dev_notify_flags+0x18d/0x2e0
 netif_change_flags+0xe8/0x1a0
 dev_change_flags+0x130/0x260
 dev_ioctl+0x7b4/0x1150
 sock_do_ioctl+0x22c/0x300
 sock_ioctl+0x576/0x790
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0xfa0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdd5298f6c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fdd537dd038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fdd52be6180 RCX: 00007fdd5298f6c9
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 0000000000000004
RBP: 00007fdd52a11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdd52be6218 R14: 00007fdd52be6180 R15: 00007ffd2b135868
 </TASK>
