R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

============================================
WARNING: possible recursive locking detected
4.15.0-rc7+ #170 Not tainted
--------------------------------------------
syz-executor6/5948 is trying to acquire lock:
 (&pn->all_ppp_mutex){+.+.}, at: [<00000000c7a2e0bd>] ppp_dev_uninit+0x23a/0x440 drivers/net/ppp/ppp_generic.c:1369

but task is already holding lock:
 (&pn->all_ppp_mutex){+.+.}, at: [<00000000a997f1b5>] ppp_unit_register drivers/net/ppp/ppp_generic.c:981 [inline]
 (&pn->all_ppp_mutex){+.+.}, at: [<00000000a997f1b5>] 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-executor6/5948:
 #0:  (ppp_mutex){+.+.}, at: [<00000000ed1b05c1>] ppp_ioctl+0x16d/0x2a50 drivers/net/ppp/ppp_generic.c:598
 #1:  (rtnl_mutex){+.+.}, at: [<00000000eba07092>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:72
 #2:  (&pn->all_ppp_mutex){+.+.}, at: [<00000000a997f1b5>] ppp_unit_register drivers/net/ppp/ppp_generic.c:981 [inline]
 #2:  (&pn->all_ppp_mutex){+.+.}, at: [<00000000a997f1b5>] ppp_dev_configure+0x74e/0xdd0 drivers/net/ppp/ppp_generic.c:1066

stack backtrace:
CPU: 0 PID: 5948 Comm: syz-executor6 Not tainted 4.15.0-rc7+ #170
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+0x937/0x1010 net/core/dev.c:7758
 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
 C_SYSC_ioctl fs/compat_ioctl.c:1495 [inline]
 compat_SyS_ioctl+0x4ef/0x2a30 fs/compat_ioctl.c:1419
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:129
RIP: 0023:0xf7fcec79
RSP: 002b:00000000f77ca08c EFLAGS: 00000296 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000014 RCX: 00000000c004743e
RDX: 0000000020001000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000