======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17368/12867 is trying to acquire lock:
ffffffff8fd49b18 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x40c/0xf90

but task is already holding lock:
ffff88810d5ab370 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x215/0xf90

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{3:3}:
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_ioctl+0x215/0xf90
       sock_do_ioctl+0x101/0x320
       sock_ioctl+0x5c6/0x7f0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_node_list_lock){+...}-{3:3}:
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_device_down+0xbe/0x860
       nr_device_event+0x137/0x150
       notifier_call_chain+0x1be/0x400
       __dev_notify_flags+0x16d/0x310
       netif_change_flags+0xe8/0x1a0
       dev_change_flags+0x130/0x260
       dev_ioctl+0x7b4/0x1150
       sock_do_ioctl+0x23e/0x320
       sock_ioctl+0x5c6/0x7f0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x14d/0xf80
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_neigh_list_lock){+...}-{3:3}:
       __lock_acquire+0x15a5/0x2cf0
       lock_acquire+0xf0/0x2e0
       _raw_spin_lock_bh+0x36/0x50
       nr_rt_ioctl+0x40c/0xf90
       sock_do_ioctl+0x101/0x320
       sock_ioctl+0x5c6/0x7f0
       __se_sys_ioctl+0xfc/0x170
       do_syscall_64+0x14d/0xf80
       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.0.17368/12867:
 #0: ffffffff8fd49b78 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x15f/0xf90
 #1: ffff88810d5ab370 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x215/0xf90

stack backtrace:
CPU: 1 UID: 0 PID: 12867 Comm: syz.0.17368 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+0xe8/0x150
 print_circular_bug+0x2e1/0x300
 check_noncircular+0x12e/0x150
 __lock_acquire+0x15a5/0x2cf0
 lock_acquire+0xf0/0x2e0
 _raw_spin_lock_bh+0x36/0x50
 nr_rt_ioctl+0x40c/0xf90
 sock_do_ioctl+0x101/0x320
 sock_ioctl+0x5c6/0x7f0
 __se_sys_ioctl+0xfc/0x170
 do_syscall_64+0x14d/0xf80
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f7870d9c799
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f7871cc2028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f7871015fa0 RCX: 00007f7870d9c799
RDX: 0000000000000000 RSI: 00000000000089e2 RDI: 0000000000000004
RBP: 00007f7870e32bd9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7871016038 R14: 00007f7871015fa0 R15: 00007ffcdd7971d8
 </TASK>
