======================================================
WARNING: possible circular locking dependency detected
6.1.137-syzkaller #0 Not tainted
------------------------------------------------------
syz.0.1167/7958 is trying to acquire lock:
ffffffff8dc82118 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8dc82118 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh+0x25/0xe0 net/netrom/nr_route.c:307

but task is already holding lock:
ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: nr_add_node+0xccf/0x24b0 net/netrom/nr_route.c:214

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&nr_node->node_lock){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x32/0x50 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+0x126/0x710 net/netrom/nr_route.c:519
       nr_device_event+0x133/0x140 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:87 [inline]
       raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
       call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
       call_netdevice_notifiers net/core/dev.c:2053 [inline]
       __dev_notify_flags+0x178/0x2d0 net/core/dev.c:-1
       dev_change_flags+0xe3/0x1a0 net/core/dev.c:8702
       dev_ifsioc+0x159/0xe90 net/core/dev_ioctl.c:327
       dev_ioctl+0x578/0xea0 net/core/dev_ioctl.c:588
       sock_do_ioctl+0x222/0x2f0 net/socket.c:1218
       sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (nr_node_list_lock){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x32/0x50 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xa5/0x710 net/netrom/nr_route.c:517
       nr_device_event+0x133/0x140 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:87 [inline]
       raw_notifier_call_chain+0xcb/0x160 kernel/notifier.c:455
       call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
       call_netdevice_notifiers net/core/dev.c:2053 [inline]
       __dev_notify_flags+0x178/0x2d0 net/core/dev.c:-1
       dev_change_flags+0xe3/0x1a0 net/core/dev.c:8702
       dev_ifsioc+0x159/0xe90 net/core/dev_ioctl.c:327
       dev_ioctl+0x578/0xea0 net/core/dev_ioctl.c:588
       sock_do_ioctl+0x222/0x2f0 net/socket.c:1218
       sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (nr_neigh_list_lock){+...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3090 [inline]
       check_prevs_add kernel/locking/lockdep.c:3209 [inline]
       validate_chain kernel/locking/lockdep.c:3825 [inline]
       __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
       lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x32/0x50 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+0x1d2d/0x24b0 net/netrom/nr_route.c:249
       nr_rt_ioctl+0xc0b/0xd40 net/netrom/nr_route.c:651
       sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
       sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
       do_syscall_x64 arch/x86/entry/common.c:51 [inline]
       do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

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 ***

1 lock held by syz.0.1167/7958:
 #0: ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #0: ffff888143f6ac70 (&nr_node->node_lock){+...}-{2:2}, at: nr_add_node+0xccf/0x24b0 net/netrom/nr_route.c:214

stack backtrace:
CPU: 0 PID: 7958 Comm: syz.0.1167 Not tainted 6.1.137-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/19/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 check_noncircular+0x274/0x310 kernel/locking/lockdep.c:2170
 check_prev_add kernel/locking/lockdep.c:3090 [inline]
 check_prevs_add kernel/locking/lockdep.c:3209 [inline]
 validate_chain kernel/locking/lockdep.c:3825 [inline]
 __lock_acquire+0x2cf8/0x7c50 kernel/locking/lockdep.c:5049
 lock_acquire+0x1b4/0x490 kernel/locking/lockdep.c:5662
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x32/0x50 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+0x1d2d/0x24b0 net/netrom/nr_route.c:249
 nr_rt_ioctl+0xc0b/0xd40 net/netrom/nr_route.c:651
 sock_do_ioctl+0xd3/0x2f0 net/socket.c:1204
 sock_ioctl+0x4ed/0x6e0 net/socket.c:1321
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl+0xfa/0x170 fs/ioctl.c:856
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f85d218e969
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:00007f85d3084038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f85d23b5fa0 RCX: 00007f85d218e969
RDX: 0000200000000280 RSI: 000000000000890b RDI: 0000000000000004
RBP: 00007f85d2210ab1 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f85d23b5fa0 R15: 00007ffc7b29feb8
 </TASK>