======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.9961/12176 is trying to acquire lock:
ffffffff8fb28318 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8fb28318 (nr_neigh_list_lock){+...}-{3:3}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffffffff8fb28318 (nr_neigh_list_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:472 [inline]
ffffffff8fb28318 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x40c/0xf90 net/netrom/nr_route.c:692

but task is already holding lock:
ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x215/0xf90 net/netrom/nr_route.c:692

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 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_dec_obs net/netrom/nr_route.c:459 [inline]
       nr_rt_ioctl+0x215/0xf90 net/netrom/nr_route.c:692
       sock_do_ioctl+0x101/0x320 net/socket.c:1254
       sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #1 (nr_node_list_lock){+...}-{3:3}:
       __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+0xbe/0x860 net/netrom/nr_route.c:517
       nr_device_event+0x137/0x150 net/netrom/af_netrom.c:126
       notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
       call_netdevice_notifiers_extack net/core/dev.c:2280 [inline]
       call_netdevice_notifiers net/core/dev.c:2294 [inline]
       __dev_notify_flags+0x16d/0x310 net/core/dev.c:9789
       netif_change_flags+0xe8/0x1a0 net/core/dev.c:9816
       dev_change_flags+0x130/0x260 net/core/dev_api.c:68
       dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:814
       sock_do_ioctl+0x23e/0x320 net/socket.c:1268
       sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (nr_neigh_list_lock){+...}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3165 [inline]
       check_prevs_add kernel/locking/lockdep.c:3284 [inline]
       validate_chain kernel/locking/lockdep.c:3908 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
       lock_acquire+0x106/0x330 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 net/netrom/nr_route.c:307 [inline]
       nr_dec_obs net/netrom/nr_route.c:472 [inline]
       nr_rt_ioctl+0x40c/0xf90 net/netrom/nr_route.c:692
       sock_do_ioctl+0x101/0x320 net/socket.c:1254
       sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0xe2/0xf80 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_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.0.9961/12176:
 #0: ffffffff8fb28378 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffffffff8fb28378 (nr_node_list_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:457 [inline]
 #0: ffffffff8fb28378 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x15f/0xf90 net/netrom/nr_route.c:692
 #1: ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #1: ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
 #1: ffff88808f9c8770 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x215/0xf90 net/netrom/nr_route.c:692

stack backtrace:
CPU: 1 UID: 0 PID: 12176 Comm: syz.0.9961 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043
 check_noncircular+0x12e/0x150 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 kernel/locking/lockdep.c:3908 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237
 lock_acquire+0x106/0x330 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 net/netrom/nr_route.c:307 [inline]
 nr_dec_obs net/netrom/nr_route.c:472 [inline]
 nr_rt_ioctl+0x40c/0xf90 net/netrom/nr_route.c:692
 sock_do_ioctl+0x101/0x320 net/socket.c:1254
 sock_ioctl+0x5c6/0x7f0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f196559aeb9
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:00007f1966504028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f1965815fa0 RCX: 00007f196559aeb9
RDX: 0000200000000100 RSI: 00000000000089e2 RDI: 0000000000000006
RBP: 00007f1965608c1f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1965816038 R14: 00007f1965815fa0 R15: 00007ffed529d9c8
 </TASK>
tipc: Enabling of bearer <eth:syzkaller0> rejected, already enabled