============================================
WARNING: possible recursive locking detected
5.15.98-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.0/11213 is trying to acquire lock:
ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1649 [inline]
ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: l2tp_tunnel_register+0xafb/0x1c90 net/l2tp/l2tp_core.c:1485

but task is already holding lock:
ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1649 [inline]
ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0x65b/0x1680 net/l2tp/l2tp_ppp.c:676

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

       CPU0
       ----
  lock(sk_lock-AF_PPPOX);
  lock(sk_lock-AF_PPPOX);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz-executor.0/11213:
 #0: ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1649 [inline]
 #0: ffff88802a6ba120 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0x65b/0x1680 net/l2tp/l2tp_ppp.c:676

stack backtrace:
CPU: 0 PID: 11213 Comm: syz-executor.0 Not tainted 5.15.98-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/02/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2946 [inline]
 check_deadlock kernel/locking/lockdep.c:2989 [inline]
 validate_chain+0x46cf/0x58b0 kernel/locking/lockdep.c:3774
 __lock_acquire+0x1295/0x1ff0 kernel/locking/lockdep.c:5011
 lock_acquire+0x1f6/0x560 kernel/locking/lockdep.c:5622
 lock_sock_nested+0x44/0x100 net/core/sock.c:3207
 lock_sock include/net/sock.h:1649 [inline]
 l2tp_tunnel_register+0xafb/0x1c90 net/l2tp/l2tp_core.c:1485
 pppol2tp_connect+0xafb/0x1680 net/l2tp/l2tp_ppp.c:724
 __sys_connect_file net/socket.c:1899 [inline]
 __sys_connect+0x38b/0x410 net/socket.c:1916
 __do_sys_connect net/socket.c:1926 [inline]
 __se_sys_connect net/socket.c:1923 [inline]
 __x64_sys_connect+0x76/0x80 net/socket.c:1923
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f1cc20f40f9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 00 00 90 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1cc0666168 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f1cc2213f80 RCX: 00007f1cc20f40f9
RDX: 0000000000000032 RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00007f1cc214fae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffdfebc9ecf R14: 00007f1cc0666300 R15: 0000000000022000
 </TASK>