syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.2292/10680 is trying to acquire lock:
ffff8880205d9c70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff8880205d9c70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff8880205d9c70 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_device_down+0x12a/0x720 net/netrom/nr_route.c:519

but task is already holding lock:
ffffffff8e119c78 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffffffff8e119c78 (nr_node_list_lock){+...}-{2:2}, 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){+...}-{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_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+0x197/0x390 kernel/notifier.c:93
       call_netdevice_notifiers_extack net/core/dev.c:2064 [inline]
       call_netdevice_notifiers net/core/dev.c:2078 [inline]
       __dev_notify_flags+0x18e/0x2e0 net/core/dev.c:-1
       dev_change_flags+0xe8/0x1a0 net/core/dev.c:8762
       dev_ifsioc+0x6a7/0xe20 net/core/dev_ioctl.c:529
       dev_ioctl+0x7e2/0x1170 net/core/dev_ioctl.c:786
       sock_do_ioctl+0x226/0x2f0 net/socket.c:1236
       sock_ioctl+0x623/0x7a0 net/socket.c:1341
       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:51 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #1 (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+0x25/0xe0 net/netrom/nr_route.c:307
       nr_add_node+0x1d2d/0x24b0 net/netrom/nr_route.c:249
       nr_rt_ioctl+0xc0f/0xd40 net/netrom/nr_route.c:651
       sock_do_ioctl+0xd7/0x2f0 net/socket.c:1222
       sock_ioctl+0x623/0x7a0 net/socket.c:1341
       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:51 [inline]
       do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
       entry_SYSCALL_64_after_hwframe+0x68/0xd2

-> #0 (&nr_node->node_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+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
       lock_acquire+0x197/0x410 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_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+0x197/0x390 kernel/notifier.c:93
       call_netdevice_notifiers_extack net/core/dev.c:2064 [inline]
       call_netdevice_notifiers net/core/dev.c:2078 [inline]
       __dev_notify_flags+0x18e/0x2e0 net/core/dev.c:-1
       dev_change_flags+0xe8/0x1a0 net/core/dev.c:8762
       dev_ifsioc+0x6a7/0xe20 net/core/dev_ioctl.c:529
       dev_ioctl+0x7e2/0x1170 net/core/dev_ioctl.c:786
       sock_do_ioctl+0x226/0x2f0 net/socket.c:1236
       sock_ioctl+0x623/0x7a0 net/socket.c:1341
       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:51 [inline]
       do_syscall_64+0x55/0xb0 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_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.1.2292/10680:
 #0: ffffffff8dfbc908 (rtnl_mutex){+.+.}-{3:3}, at: dev_ioctl+0x7d2/0x1170 net/core/dev_ioctl.c:785
 #1: ffffffff8e119c18 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffffffff8e119c18 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x28/0x720 net/netrom/nr_route.c:514
 #2: ffffffff8e119c78 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #2: ffffffff8e119c78 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xa9/0x720 net/netrom/nr_route.c:517

stack backtrace:
CPU: 1 PID: 10680 Comm: syz.1.2292 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 check_noncircular+0x2bd/0x3c0 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+0x2ddb/0x7c80 kernel/locking/lockdep.c:5137
 lock_acquire+0x197/0x410 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_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+0x197/0x390 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2064 [inline]
 call_netdevice_notifiers net/core/dev.c:2078 [inline]
 __dev_notify_flags+0x18e/0x2e0 net/core/dev.c:-1
 dev_change_flags+0xe8/0x1a0 net/core/dev.c:8762
 dev_ifsioc+0x6a7/0xe20 net/core/dev_ioctl.c:529
 dev_ioctl+0x7e2/0x1170 net/core/dev_ioctl.c:786
 sock_do_ioctl+0x226/0x2f0 net/socket.c:1236
 sock_ioctl+0x623/0x7a0 net/socket.c:1341
 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:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f41a618eba9
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:00007f41a7084038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f41a63d5fa0 RCX: 00007f41a618eba9
RDX: 0000200000000000 RSI: 0000000000008914 RDI: 0000000000000006
RBP: 00007f41a6211e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f41a63d6038 R14: 00007f41a63d5fa0 R15: 00007ffc1e84e1d8
 </TASK>