syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.1.1653/9530 is trying to acquire lock:
ffff8000179b37b8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff8000179b37b8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_remove_neigh net/netrom/nr_route.c:307 [inline]
ffff8000179b37b8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:472 [inline]
ffff8000179b37b8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x32c/0xbb4 net/netrom/nr_route.c:692

but task is already holding lock:
ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1c0/0xbb4 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){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x54/0x6c 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+0x128/0x658 net/netrom/nr_route.c:519
       nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:87 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
       call_netdevice_notifiers_info net/core/dev.c:2001 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
       call_netdevice_notifiers net/core/dev.c:2053 [inline]
       __dev_notify_flags+0x1ec/0x480 net/core/dev.c:8678
       dev_change_flags+0xc8/0x154 net/core/dev.c:8714
       dev_ifsioc+0x138/0xc04 net/core/dev_ioctl.c:326
       dev_ioctl+0x4b0/0xc74 net/core/dev_ioctl.c:572
       sock_do_ioctl+0x198/0x258 net/socket.c:1215
       sock_ioctl+0x238/0x824 net/socket.c:1320
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl fs/ioctl.c:856 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #1 (nr_node_list_lock){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x54/0x6c kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:356 [inline]
       nr_rt_device_down+0xb4/0x658 net/netrom/nr_route.c:517
       nr_device_event+0x138/0x164 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:87 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:455
       call_netdevice_notifiers_info net/core/dev.c:2001 [inline]
       call_netdevice_notifiers_extack net/core/dev.c:2039 [inline]
       call_netdevice_notifiers net/core/dev.c:2053 [inline]
       __dev_notify_flags+0x1ec/0x480 net/core/dev.c:8678
       dev_change_flags+0xc8/0x154 net/core/dev.c:8714
       dev_ifsioc+0x138/0xc04 net/core/dev_ioctl.c:326
       dev_ioctl+0x4b0/0xc74 net/core/dev_ioctl.c:572
       sock_do_ioctl+0x198/0x258 net/socket.c:1215
       sock_ioctl+0x238/0x824 net/socket.c:1320
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl fs/ioctl.c:856 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

-> #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+0x2880/0x6800 kernel/locking/lockdep.c:5049
       lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
       _raw_spin_lock_bh+0x54/0x6c 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+0x32c/0xbb4 net/netrom/nr_route.c:692
       nr_ioctl+0x19c/0x474 net/netrom/af_netrom.c:1254
       sock_do_ioctl+0x100/0x258 net/socket.c:1201
       sock_ioctl+0x238/0x824 net/socket.c:1320
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:870 [inline]
       __se_sys_ioctl fs/ioctl.c:856 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
       do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
       el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
       el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
       el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

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.1.1653/9530:
 #0: ffff8000179b3818 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #0: ffff8000179b3818 (nr_node_list_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:457 [inline]
 #0: ffff8000179b3818 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_ioctl+0x124/0xbb4 net/netrom/nr_route.c:692
 #1: ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:356 [inline]
 #1: ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:152 [inline]
 #1: ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_dec_obs net/netrom/nr_route.c:459 [inline]
 #1: ffff0000dc6aa670 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_ioctl+0x1c0/0xbb4 net/netrom/nr_route.c:692

stack backtrace:
CPU: 0 PID: 9530 Comm: syz.1.1653 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 dump_backtrace+0x1c0/0x1ec arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 dump_stack+0x1c/0x5c lib/dump_stack.c:113
 print_circular_bug+0x148/0x1b0 kernel/locking/lockdep.c:2048
 check_noncircular+0x264/0x2f8 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+0x2880/0x6800 kernel/locking/lockdep.c:5049
 lock_acquire+0x20c/0x63c kernel/locking/lockdep.c:5662
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:126 [inline]
 _raw_spin_lock_bh+0x54/0x6c 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+0x32c/0xbb4 net/netrom/nr_route.c:692
 nr_ioctl+0x19c/0x474 net/netrom/af_netrom.c:1254
 sock_do_ioctl+0x100/0x258 net/socket.c:1201
 sock_ioctl+0x238/0x824 net/socket.c:1320
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:870 [inline]
 __se_sys_ioctl fs/ioctl.c:856 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:856
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585