syzbot

============================================
WARNING: possible recursive locking detected
6.14.0-rc5-syzkaller-01183-g40587f749df2 #0 Not tainted
--------------------------------------------
dhcpcd/5501 is trying to acquire lock:
ffff88802a344d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
ffff88802a344d28 (&dev->lock){+.+.}-{4:4}, at: netif_napi_add_weight include/linux/netdevice.h:2763 [inline]
ffff88802a344d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
ffff88802a344d28 (&dev->lock){+.+.}-{4:4}, at: lapbeth_device_event+0x766/0xa20 drivers/net/wan/lapbether.c:460

but task is already holding lock:
ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:40 [inline]
ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0x120/0x270 net/core/dev_api.c:67

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->lock);
  lock(&dev->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by dhcpcd/5501:
 #0: ffffffff8fed6908 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_net_lock include/linux/rtnetlink.h:130 [inline]
 #0: ffffffff8fed6908 (rtnl_mutex){+.+.}-{4:4}, at: devinet_ioctl+0x34c/0x1d80 net/ipv4/devinet.c:1121
 #1: ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock include/linux/netdevice.h:2731 [inline]
 #1: ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: netdev_lock_ops include/net/netdev_lock.h:40 [inline]
 #1: ffff888065558d28 (&dev->lock){+.+.}-{4:4}, at: dev_change_flags+0x120/0x270 net/core/dev_api.c:67

stack backtrace:
CPU: 1 UID: 0 PID: 5501 Comm: dhcpcd Not tainted 6.14.0-rc5-syzkaller-01183-g40587f749df2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
 check_deadlock kernel/locking/lockdep.c:3091 [inline]
 validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 __mutex_lock_common kernel/locking/mutex.c:585 [inline]
 __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
 netdev_lock include/linux/netdevice.h:2731 [inline]
 netif_napi_add_weight include/linux/netdevice.h:2763 [inline]
 lapbeth_new_device drivers/net/wan/lapbether.c:415 [inline]
 lapbeth_device_event+0x766/0xa20 drivers/net/wan/lapbether.c:460
 notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85
 __dev_notify_flags+0x207/0x400
 netif_change_flags+0xf0/0x1a0 net/core/dev.c:9443
 dev_change_flags+0x146/0x270 net/core/dev_api.c:68
 devinet_ioctl+0xea2/0x1d80 net/ipv4/devinet.c:1200
 inet_ioctl+0x3d7/0x4f0 net/ipv4/af_inet.c:1001
 sock_do_ioctl+0x158/0x460 net/socket.c:1190
 sock_ioctl+0x626/0x8e0 net/socket.c:1309
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:906 [inline]
 __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fecff09ad49
Code: 5c c3 48 8d 44 24 08 48 89 54 24 e0 48 89 44 24 c0 48 8d 44 24 d0 48 89 44 24 c8 b8 10 00 00 00 c7 44 24 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 76 10 48 8b 15 ae 60 0d 00 f7 d8 41 83 c8
RSP: 002b:00007ffd4eca2448 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fecfefcc6c0 RCX: 00007fecff09ad49
RDX: 00007ffd4ecb2638 RSI: 0000000000008914 RDI: 0000000000000010
RBP: 00007ffd4ecc27f8 R08: 00007ffd4ecb25f8 R09: 00007ffd4ecb25a8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd4ecb2638 R14: 0000000000000028 R15: 0000000000008914
 </TASK>