R10: 0000000000000000 R11: 0000000000000212 R12: 00000000004b77ef
R13: 00007fceaf45dac8 R14: 00000000004b77fa R15: 0000000000000000

============================================
WARNING: possible recursive locking detected
4.15.0-rc7-mm1+ #56 Not tainted
--------------------------------------------
syz-executor3/8133 is trying to acquire lock:
 (&pn->all_ppp_mutex){+.+.}, at: [<00000000150d621b>] ppp_dev_uninit+0x23a/0x440 drivers/net/ppp/ppp_generic.c:1369

but task is already holding lock:
 (&pn->all_ppp_mutex){+.+.}, at: [<0000000017ec71af>] ppp_unit_register drivers/net/ppp/ppp_generic.c:981 [inline]
 (&pn->all_ppp_mutex){+.+.}, at: [<0000000017ec71af>] ppp_dev_configure+0x74e/0xdd0 drivers/net/ppp/ppp_generic.c:1066

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

       CPU0
       ----
  lock(&pn->all_ppp_mutex);
  lock(&pn->all_ppp_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor3/8133:
 #0:  (ppp_mutex){+.+.}, at: [<000000003e36cf52>] ppp_ioctl+0x16d/0x2a50 drivers/net/ppp/ppp_generic.c:598
 #1:  (rtnl_mutex){+.+.}, at: [<0000000033f338a2>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:74
 #2:  (&pn->all_ppp_mutex){+.+.}, at: [<0000000017ec71af>] ppp_unit_register drivers/net/ppp/ppp_generic.c:981 [inline]
 #2:  (&pn->all_ppp_mutex){+.+.}, at: [<0000000017ec71af>] ppp_dev_configure+0x74e/0xdd0 drivers/net/ppp/ppp_generic.c:1066

stack backtrace:
CPU: 0 PID: 8133 Comm: syz-executor3 Not tainted 4.15.0-rc7-mm1+ #56
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_deadlock_bug kernel/locking/lockdep.c:1756 [inline]
 check_deadlock kernel/locking/lockdep.c:1800 [inline]
 validate_chain kernel/locking/lockdep.c:2396 [inline]
 __lock_acquire+0xe8f/0x3e00 kernel/locking/lockdep.c:3426
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 ppp_dev_uninit+0x23a/0x440 drivers/net/ppp/ppp_generic.c:1369
 register_netdevice+0x937/0x1020 net/core/dev.c:7889
 ppp_unit_register drivers/net/ppp/ppp_generic.c:1009 [inline]
 ppp_dev_configure+0x964/0xdd0 drivers/net/ppp/ppp_generic.c:1066
 ppp_create_interface drivers/net/ppp/ppp_generic.c:3027 [inline]
 ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:866 [inline]
 ppp_ioctl+0x178f/0x2a50 drivers/net/ppp/ppp_generic.c:602
 vfs_ioctl fs/ioctl.c:46 [inline]
 do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
 SYSC_ioctl fs/ioctl.c:701 [inline]
 SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
 entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x452df9
RSP: 002b:00007fceaf45dc58 EFLAGS: 00000212 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007fceaf45d950 RCX: 0000000000452df9
RDX: 0000000020000f0a RSI: 00000000c004743e RDI: 0000000000000016
RBP: 00007fceaf45d940 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000004b77ef
R13: 00007fceaf45dac8 R14: 00000000004b77fa R15: 0000000000000000