============================================
WARNING: possible recursive locking detected
6.2.0-rc8-next-20230220-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.1/10168 is trying to acquire lock:
ffff8880549da130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1697 [inline]
ffff8880549da130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: l2tp_tunnel_register+0x1af/0xd80 net/l2tp/l2tp_core.c:1483

but task is already holding lock:
ffff8880549dc130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1697 [inline]
ffff8880549dc130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xadc/0x1a80 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.1/10168:
 #0: ffff8880549dc130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1697 [inline]
 #0: ffff8880549dc130 (sk_lock-AF_PPPOX){+.+.}-{0:0}, at: pppol2tp_connect+0xadc/0x1a80 net/l2tp/l2tp_ppp.c:675

stack backtrace:
CPU: 1 PID: 10168 Comm: syz-executor.1 Not tainted 6.2.0-rc8-next-20230220-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/21/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
 print_deadlock_bug kernel/locking/lockdep.c:2991 [inline]
 check_deadlock kernel/locking/lockdep.c:3034 [inline]
 validate_chain kernel/locking/lockdep.c:3819 [inline]
 __lock_acquire+0x1362/0x5d40 kernel/locking/lockdep.c:5056
 lock_acquire.part.0+0x11a/0x370 kernel/locking/lockdep.c:5669
 lock_sock_nested+0x3a/0xf0 net/core/sock.c:3473
 lock_sock include/net/sock.h:1697 [inline]
 l2tp_tunnel_register+0x1af/0xd80 net/l2tp/l2tp_core.c:1483
 pppol2tp_connect+0xcdc/0x1a80 net/l2tp/l2tp_ppp.c:723
 __sys_connect_file+0x153/0x1a0 net/socket.c:2004
 __sys_connect+0x165/0x1a0 net/socket.c:2021
 __do_sys_connect net/socket.c:2031 [inline]
 __se_sys_connect net/socket.c:2028 [inline]
 __x64_sys_connect+0x73/0xb0 net/socket.c:2028
 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: 0033:0x7f705408c0f9
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:00007f7054deb168 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f70541abf80 RCX: 00007f705408c0f9
RDX: 0000000000000026 RSI: 00000000200000c0 RDI: 0000000000000004
RBP: 00007f70540e7ae9 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ffe481a550f R14: 00007f7054deb300 R15: 0000000000022000
 </TASK>