======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.481/8754 is trying to acquire lock:
ffff8000929e3c18 (nr_neigh_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff8000929e3c18 (nr_neigh_list_lock){+...}-{3:3}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffff8000929e3c18 (nr_neigh_list_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:472 [inline]
ffff8000929e3c18 (nr_neigh_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x2e4/0x9d8 net/netrom/nr_route.c:692

but task is already holding lock:
ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x178/0x9d8 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+0x48/0x60 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+0x128/0x660 net/netrom/nr_route.c:519
       nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
       notifier_call_chain+0x1b8/0x4e4 kernel/notifier.c:85
       raw_notifier_call_chain+0x3c/0x50 kernel/notifier.c:453
       call_netdevice_notifiers_info net/core/dev.c:2229 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x260/0x47c net/core/dev.c:-1
       netif_change_flags+0xd0/0x15c net/core/dev.c:9705
       dev_change_flags+0x10c/0x204 net/core/dev_api.c:68
       dev_ifsioc+0xd8/0xb90 net/core/dev_ioctl.c:582
       dev_ioctl+0x4b0/0xc74 net/core/dev_ioctl.c:841
       sock_do_ioctl+0x200/0x2b4 net/socket.c:1268
       sock_ioctl+0x57c/0x84c net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #1 (nr_node_list_lock){+...}-{3:3}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x48/0x60 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xb4/0x660 net/netrom/nr_route.c:517
       nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
       notifier_call_chain+0x1b8/0x4e4 kernel/notifier.c:85
       raw_notifier_call_chain+0x3c/0x50 kernel/notifier.c:453
       call_netdevice_notifiers_info net/core/dev.c:2229 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2267 [inline]
       call_netdevice_notifiers net/core/dev.c:2281 [inline]
       __dev_notify_flags+0x260/0x47c net/core/dev.c:-1
       netif_change_flags+0xd0/0x15c net/core/dev.c:9705
       dev_change_flags+0x10c/0x204 net/core/dev_api.c:68
       dev_ifsioc+0xd8/0xb90 net/core/dev_ioctl.c:582
       dev_ioctl+0x4b0/0xc74 net/core/dev_ioctl.c:841
       sock_do_ioctl+0x200/0x2b4 net/socket.c:1268
       sock_ioctl+0x57c/0x84c net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

-> #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+0x1774/0x30a4 kernel/locking/lockdep.c:5237
       lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x48/0x60 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+0x2e4/0x9d8 net/netrom/nr_route.c:692
       nr_ioctl+0x1c4/0x500 net/netrom/af_netrom.c:1254
       sock_do_ioctl+0xf4/0x2b4 net/socket.c:1254
       sock_ioctl+0x57c/0x84c net/socket.c:1375
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:597 [inline]
       __se_sys_ioctl fs/ioctl.c:583 [inline]
       __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
       __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
       invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
       el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
       do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
       el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
       el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
       el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

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.0.481/8754:
 #0: ffff8000929e3c78 (nr_node_list_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffff8000929e3c78 (nr_node_list_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:457 [inline]
 #0: ffff8000929e3c78 (nr_node_list_lock){+...}-{3:3}, at: nr_rt_ioctl+0x100/0x9d8 net/netrom/nr_route.c:692
 #1: ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #1: ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
 #1: ffff0000d5fc8c70 (&nr_node->node_lock){+...}-{3:3}, at: nr_rt_ioctl+0x178/0x9d8 net/netrom/nr_route.c:692

stack backtrace:
CPU: 0 UID: 0 PID: 8754 Comm: syz.0.481 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 dump_stack+0x1c/0x28 lib/dump_stack.c:129
 print_circular_bug+0x324/0x32c kernel/locking/lockdep.c:2043
 check_noncircular+0x154/0x174 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+0x1774/0x30a4 kernel/locking/lockdep.c:5237
 lock_acquire+0x14c/0x2e0 kernel/locking/lockdep.c:5868
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x48/0x60 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+0x2e4/0x9d8 net/netrom/nr_route.c:692
 nr_ioctl+0x1c4/0x500 net/netrom/af_netrom.c:1254
 sock_do_ioctl+0xf4/0x2b4 net/socket.c:1254
 sock_ioctl+0x57c/0x84c net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __arm64_sys_ioctl+0x14c/0x1c4 fs/ioctl.c:583
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xe8/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:724
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:743
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596