syzbot

======================================================
WARNING: possible circular locking dependency detected
5.15.158-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor135/4064 is trying to acquire lock:
ffff0000c1421e70 (&nr_node->node_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff0000c1421e70 (&nr_node->node_lock){+...}-{2:2}, at: nr_node_lock include/net/netrom.h:151 [inline]
ffff0000c1421e70 (&nr_node->node_lock){+...}-{2:2}, at: nr_rt_device_down+0x144/0x8fc net/netrom/nr_route.c:524

but task is already holding lock:
ffff800016b6ad58 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
ffff800016b6ad58 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xb4/0x8fc net/netrom/nr_route.c:522

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (nr_node_list_lock){+...}-{2:2}:
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
       _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:368 [inline]
       nr_remove_node net/netrom/nr_route.c:299 [inline]
       nr_del_node net/netrom/nr_route.c:355 [inline]
       nr_rt_ioctl+0x13c4/0x1b0c net/netrom/nr_route.c:683
       nr_ioctl+0x14c/0x4b0 net/netrom/af_netrom.c:1253
       sock_do_ioctl+0x134/0x2dc net/socket.c:1140
       sock_ioctl+0x4f0/0x8ac net/socket.c:1257
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

-> #0 (&nr_node->node_lock){+...}-{2:2}:
       check_prev_add kernel/locking/lockdep.c:3053 [inline]
       check_prevs_add kernel/locking/lockdep.c:3172 [inline]
       validate_chain kernel/locking/lockdep.c:3788 [inline]
       __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
       lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
       __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
       _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
       spin_lock_bh include/linux/spinlock.h:368 [inline]
       nr_node_lock include/net/netrom.h:151 [inline]
       nr_rt_device_down+0x144/0x8fc net/netrom/nr_route.c:524
       nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
       notifier_call_chain kernel/notifier.c:83 [inline]
       raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
       __dev_notify_flags+0x2ac/0x534
       dev_change_flags+0xc8/0x154 net/core/dev.c:8889
       dev_ifsioc+0x140/0xfe4 net/core/dev_ioctl.c:324
       dev_ioctl+0x4e0/0xd3c net/core/dev_ioctl.c:587
       sock_do_ioctl+0x1dc/0x2dc net/socket.c:1154
       sock_ioctl+0x4f0/0x8ac net/socket.c:1257
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:874 [inline]
       __se_sys_ioctl fs/ioctl.c:860 [inline]
       __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
       __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
       invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
       el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
       do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
       el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
       el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
       el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

3 locks held by syz-executor135/4064:
 #0: ffff800016a36668 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock+0x20/0x2c net/core/rtnetlink.c:72
 #1: ffff800016b6acf8 (nr_neigh_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
 #1: ffff800016b6acf8 (nr_neigh_list_lock){+...}-{2:2}, at: nr_rt_device_down+0x38/0x8fc net/netrom/nr_route.c:519
 #2: ffff800016b6ad58 (nr_node_list_lock){+...}-{2:2}, at: spin_lock_bh include/linux/spinlock.h:368 [inline]
 #2: ffff800016b6ad58 (nr_node_list_lock){+...}-{2:2}, at: nr_rt_device_down+0xb4/0x8fc net/netrom/nr_route.c:522

stack backtrace:
CPU: 0 PID: 4064 Comm: syz-executor135 Not tainted 5.15.158-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
Call trace:
 dump_backtrace+0x0/0x530 arch/arm64/kernel/stacktrace.c:152
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:216
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x108/0x170 lib/dump_stack.c:106
 dump_stack+0x1c/0x58 lib/dump_stack.c:113
 print_circular_bug+0x150/0x1b8 kernel/locking/lockdep.c:2011
 check_noncircular+0x2cc/0x378 kernel/locking/lockdep.c:2133
 check_prev_add kernel/locking/lockdep.c:3053 [inline]
 check_prevs_add kernel/locking/lockdep.c:3172 [inline]
 validate_chain kernel/locking/lockdep.c:3788 [inline]
 __lock_acquire+0x32d4/0x7638 kernel/locking/lockdep.c:5012
 lock_acquire+0x240/0x77c kernel/locking/lockdep.c:5623
 __raw_spin_lock_bh include/linux/spinlock_api_smp.h:135 [inline]
 _raw_spin_lock_bh+0x124/0x1c4 kernel/locking/spinlock.c:178
 spin_lock_bh include/linux/spinlock.h:368 [inline]
 nr_node_lock include/net/netrom.h:151 [inline]
 nr_rt_device_down+0x144/0x8fc net/netrom/nr_route.c:524
 nr_device_event+0x134/0x160 net/netrom/af_netrom.c:126
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0xd4/0x164 kernel/notifier.c:391
 __dev_notify_flags+0x2ac/0x534
 dev_change_flags+0xc8/0x154 net/core/dev.c:8889
 dev_ifsioc+0x140/0xfe4 net/core/dev_ioctl.c:324
 dev_ioctl+0x4e0/0xd3c net/core/dev_ioctl.c:587
 sock_do_ioctl+0x1dc/0x2dc net/socket.c:1154
 sock_ioctl+0x4f0/0x8ac net/socket.c:1257
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __arm64_sys_ioctl+0x14c/0x1c8 fs/ioctl.c:860
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:142
 do_el0_svc+0x58/0x14c arch/arm64/kernel/syscall.c:181
 el0_svc+0x7c/0x1f0 arch/arm64/kernel/entry-common.c:608
 el0t_64_sync_handler+0x84/0xe4 arch/arm64/kernel/entry-common.c:626
 el0t_64_sync+0x1a0/0x1a4 arch/arm64/kernel/entry.S:584