======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.2.986/7690 is trying to acquire lock:
ffff888055778c70 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff888055778c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff888055778c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_device_down+0x12a/0x720 net/netrom/nr_route.c:519

but task is already holding lock:
ffffffff8f8918f8 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8f8918f8 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_node_list_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517
       nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
       notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9617
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:838
       sock_do_ioctl+0x22c/0x300 net/socket.c:1252
       sock_ioctl+0x576/0x790 net/socket.c:1359
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_neigh_list_lock){+...}-{3:3}:
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_remove_neigh+0x25/0xe0 net/netrom/nr_route.c:307
       nr_add_node+0x1d9f/0x2570 net/netrom/nr_route.c:249
       nr_rt_ioctl+0xc12/0xd50 net/netrom/nr_route.c:651
       sock_do_ioctl+0xdc/0x300 net/socket.c:1238
       sock_ioctl+0x576/0x790 net/socket.c:1359
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&nr_node->node_lock){+...}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
       __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
       lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_node_lock include/net/netrom.h:152 [inline]
       nr_rt_device_down+0x12a/0x720 net/netrom/nr_route.c:519
       nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
       notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9617
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:838
       sock_do_ioctl+0x22c/0x300 net/socket.c:1252
       sock_ioctl+0x576/0x790 net/socket.c:1359
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:598 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

3 locks held by syz.2.986/7690:
 #0: ffffffff8f73c0c8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
 #0: ffffffff8f73c0c8 (rtnl_mutex){+.+.}-{4:4}, at: dev_ioctl+0x7a4/0x1150 net/core/dev_ioctl.c:837
 #1: ffffffff8f891898 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffffffff8f891898 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514
 #2: ffffffff8f8918f8 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #2: ffffffff8f8918f8 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517

stack backtrace:
CPU: 0 UID: 0 PID: 7690 Comm: syz.2.986 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
 check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
 check_prev_add kernel/locking/lockdep.c:3165 [inline]
 check_prevs_add kernel/locking/lockdep.c:3284 [inline]
 validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
 __lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
 lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x36/0x50 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:356 [inline]
 nr_node_lock include/net/netrom.h:152 [inline]
 nr_rt_device_down+0x12a/0x720 net/netrom/nr_route.c:519
 nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
 notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
 call_netdevice_notifiers net/core/dev.c:2281 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9617
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:838
 sock_do_ioctl+0x22c/0x300 net/socket.c:1252
 sock_ioctl+0x576/0x790 net/socket.c:1359
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd55538ec29
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:00007fd55614a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fd5555d5fa0 RCX: 00007fd55538ec29
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 0000000000000007
RBP: 00007fd555411e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd5555d6038 R14: 00007fd5555d5fa0 R15: 00007ffd70e3c1c8
 </TASK>