WARNING: possible recursive locking detected
6.2.0-rc8-syzkaller-00134-g38f8ccde04a3 #0 Not tainted
--------------------------------------------
syz-executor.2/5908 is trying to acquire lock:
ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1725 [inline]
ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: l2tp_tunnel_register+0x2aa/0x11e0 net/l2tp/l2tp_core.c:1483

but task is already holding lock:
ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1725 [inline]
ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xadc/0x1a10 net/l2tp/l2tp_ppp.c:675

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.2/5908:
 #0: ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1725 [inline]
 #0: ffff88807401a130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xadc/0x1a10 net/l2tp/l2tp_ppp.c:675

stack backtrace:
CPU: 0 PID: 5908 Comm: syz-executor.2 Not tainted 6.2.0-rc8-syzkaller-00134-g38f8ccde04a3 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2990 [inline]
 check_deadlock kernel/locking/lockdep.c:3033 [inline]
 validate_chain kernel/locking/lockdep.c:3818 [inline]
 __lock_acquire.cold+0x116/0x3a7 kernel/locking/lockdep.c:5055
 lock_acquire kernel/locking/lockdep.c:5668 [inline]
 lock_acquire+0x1e3/0x630 kernel/locking/lockdep.c:5633
 lock_sock_nested+0x3a/0xf0 net/core/sock.c:3471
 lock_sock include/net/sock.h:1725 [inline]
 l2tp_tunnel_register+0x2aa/0x11e0 net/l2tp/l2tp_core.c:1483
 pppol2tp_connect+0xcdc/0x1a10 net/l2tp/l2tp_ppp.c:723
 __sys_connect_file+0x153/0x1a0 net/socket.c:1979
 __sys_connect+0x165/0x1a0 net/socket.c:1996
 __do_sys_connect net/socket.c:2006 [inline]
 __se_sys_connect net/socket.c:2003 [inline]
 __x64_sys_connect+0x73/0xb0 net/socket.c:2003
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7ff58308c0f9
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:00007ff583e70168 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007ff5831abf80 RCX: 00007ff58308c0f9
RDX: 0000000000000032 RSI: 0000000020000040 RDI: 0000000000000003
RBP: 00007ff5830e7ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffd5cbd7d6f R14: 00007ff583e70300 R15: 0000000000022000
 </TASK>