======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.9752/28489 is trying to acquire lock:
ffffffff8f68f958 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x390/0xd50

but task is already holding lock:
ffff88803b3be970 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x193/0xd50

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_device_down+0x12a/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/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_node_list_lock){+...}-{3:3}:
       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/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_neigh_list_lock){+...}-{3:3}:
       validate_chain+0xb9b/0x2140
       __lock_acquire+0xab9/0xd20
       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/0x3b0
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz.0.9752/28489:
 #0: ffffffff8f68f9b8 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x104/0xd50
 #1: ffff88803b3be970 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x193/0xd50

stack backtrace:
CPU: 0 UID: 0 PID: 28489 Comm: syz.0.9752 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_ioctl+0x390/0xd50
 sock_do_ioctl+0xdc/0x300
 sock_ioctl+0x576/0x790
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5800d8ec29
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:00007f5801c02038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f5800fd5fa0 RCX: 00007f5800d8ec29
RDX: 0000000000000000 RSI: 00000000000089e2 RDI: 0000000000000004
RBP: 00007f5800e11e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5800fd6038 R14: 00007f5800fd5fa0 R15: 00007ffe464b9128
 </TASK>
