======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.6612/29838 is trying to acquire lock:
ffffffff8e51ef18 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e51ef18 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517

but task is already holding lock:
ffffffff8e51eeb8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e51eeb8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (nr_neigh_list_lock){+...}-{2:2}:
       __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+0x3e2/0xde0 net/netrom/nr_route.c:692
       sock_do_ioctl+0xfc/0x310 net/socket.c:1219
       sock_ioctl+0x5ba/0x7e0 net/socket.c:1340
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:871 [inline]
       __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (&nr_node->node_lock){+...}-{2:2}:
       __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+0x1e5/0xde0 net/netrom/nr_route.c:692
       sock_do_ioctl+0xfc/0x310 net/socket.c:1219
       sock_ioctl+0x5ba/0x7e0 net/socket.c:1340
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:871 [inline]
       __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (nr_node_list_lock){+...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3134 [inline]
       check_prevs_add kernel/locking/lockdep.c:3253 [inline]
       validate_chain kernel/locking/lockdep.c:3869 [inline]
       __lock_acquire+0x2df1/0x7d40 kernel/locking/lockdep.c:5137
       lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
       __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+0x197/0x380 kernel/notifier.c:93
       call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
       call_netdevice_notifiers net/core/dev.c:2091 [inline]
       __dev_notify_flags+0x16e/0x310 net/core/dev.c:8752
       dev_change_flags+0xe8/0x1a0 net/core/dev.c:8788
       dev_ioctl+0x7b4/0x1140 net/core/dev_ioctl.c:770
       sock_do_ioctl+0x239/0x310 net/socket.c:1233
       sock_ioctl+0x5ba/0x7e0 net/socket.c:1340
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:871 [inline]
       __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
       do_syscall_x64 arch/x86/entry/common.c:46 [inline]
       do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

other info that might help us debug this:

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

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz.0.6612/29838:
 #0: ffffffff8e3c1988 (rtnl_mutex){+.+.}-{3:3}, at: dev_ioctl+0x7a4/0x1140 net/core/dev_ioctl.c:769
 #1: ffffffff8e51eeb8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffffffff8e51eeb8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514

stack backtrace:
CPU: 1 PID: 29838 Comm: syz.0.6612 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
 check_noncircular+0x2fc/0x400 kernel/locking/lockdep.c:2187
 check_prev_add kernel/locking/lockdep.c:3134 [inline]
 check_prevs_add kernel/locking/lockdep.c:3253 [inline]
 validate_chain kernel/locking/lockdep.c:3869 [inline]
 __lock_acquire+0x2df1/0x7d40 kernel/locking/lockdep.c:5137
 lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
 __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+0x197/0x380 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
 call_netdevice_notifiers net/core/dev.c:2091 [inline]
 __dev_notify_flags+0x16e/0x310 net/core/dev.c:8752
 dev_change_flags+0xe8/0x1a0 net/core/dev.c:8788
 dev_ioctl+0x7b4/0x1140 net/core/dev_ioctl.c:770
 sock_do_ioctl+0x239/0x310 net/socket.c:1233
 sock_ioctl+0x5ba/0x7e0 net/socket.c:1340
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f8082b9c799
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:00007f8083af5028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f8082e15fa0 RCX: 00007f8082b9c799
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 000000000000000a
RBP: 00007f8082c32c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8082e16038 R14: 00007f8082e15fa0 R15: 00007ffe6ab58be8
 </TASK>