=================================
[ INFO: inconsistent lock state ]
4.9.96-g71fce1e #10 Tainted: G        W      
---------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
syz-executor7/21921 [HC0[0]:SC1[3]:HE1:SE0] takes:
 (sk_lock-AF_PPPOX){+.?.+.}, at: [<ffffffff8341b189>] lock_sock include/net/sock.h:1404 [inline]
 (sk_lock-AF_PPPOX){+.?.+.}, at: [<ffffffff8341b189>] inet_shutdown+0x69/0x360 net/ipv4/af_inet.c:823
  mark_held_locks+0xc7/0x130 kernel/locking/lockdep.c:2660
  __trace_hardirqs_on_caller kernel/locking/lockdep.c:2689 [inline]
  trace_hardirqs_on_caller+0x38b/0x590 kernel/locking/lockdep.c:2736
  trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2743
  __local_bh_enable_ip+0x6a/0xd0 kernel/softirq.c:186
  local_bh_enable include/linux/bottom_half.h:31 [inline]
  lock_sock_nested+0xdc/0x120 net/core/sock.c:2512
  lock_sock include/net/sock.h:1404 [inline]
  pppolac_release+0x52/0x400 drivers/net/ppp/pppolac.c:346
  sock_release+0x96/0x1c0 net/socket.c:599
  sock_close+0x16/0x20 net/socket.c:1046
  __fput+0x263/0x700 fs/file_table.c:208
  ____fput+0x15/0x20 fs/file_table.c:244
  task_work_run+0x10c/0x180 kernel/task_work.c:116
  exit_task_work include/linux/task_work.h:21 [inline]
  do_exit+0x9e1/0x27c0 kernel/exit.c:837
  do_group_exit+0x111/0x340 kernel/exit.c:941
  get_signal+0x4cf/0x1450 kernel/signal.c:2317
  do_signal+0x87/0x19f0 arch/x86/kernel/signal.c:807
  exit_to_usermode_loop+0xe1/0x120 arch/x86/entry/common.c:157
  prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
  syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
  do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
  entry_SYSCALL_64_after_swapgs+0x5d/0xdb
irq event stamp: 524
hardirqs last  enabled at (524): [<ffffffff839f3ca9>] restore_regs_and_iret+0x0/0x1d
hardirqs last disabled at (523): [<ffffffff839f4c6b>] apic_timer_interrupt+0x9b/0xb0 arch/x86/entry/entry_64.S:648
softirqs last  enabled at (0): [<ffffffff8112cd8a>] copy_process.part.51+0x116a/0x6330 kernel/fork.c:1617
softirqs last disabled at (415): [<ffffffff81149037>] invoke_softirq kernel/softirq.c:364 [inline]
softirqs last disabled at (415): [<ffffffff81149037>] irq_exit+0x147/0x190 kernel/softirq.c:405

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

       CPU0
       ----
  lock(sk_lock-AF_PPPOX);
  <Interrupt>
    lock(sk_lock-AF_PPPOX);

 *** DEADLOCK ***

2 locks held by syz-executor7/21921:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff830b06a7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (rcu_callback){......}, at: [<ffffffff8128586e>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128586e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128586e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128586e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff8128586e>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 21921 Comm: syz-executor7 Tainted: G        W       4.9.96-g71fce1e #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207a58 ffffffff81eb0b69 ffff8801d75a1800 ffffffff854112d0
 ffff8801d75a2118 ffff8801d75a2138 0000000000000000 ffff8801db207ac8
 ffffffff814256bb 0000000000000003 0000000000000001 ffff880100000000
Call Trace:
 <IRQ> [  267.546395]  [<ffffffff81eb0b69>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  267.546395]  [<ffffffff81eb0b69>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814256bb>] print_usage_bug.cold.56+0x327/0x421 kernel/locking/lockdep.c:2387
 [<ffffffff81233196>] valid_state kernel/locking/lockdep.c:2400 [inline]
 [<ffffffff81233196>] mark_lock_irq kernel/locking/lockdep.c:2602 [inline]
 [<ffffffff81233196>] mark_lock+0xcc6/0x1280 kernel/locking/lockdep.c:3065
 [<ffffffff812350c0>] mark_irqflags kernel/locking/lockdep.c:2923 [inline]
 [<ffffffff812350c0>] __lock_acquire+0xd40/0x4070 kernel/locking/lockdep.c:3302
 [<ffffffff81238e60>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff8301f6a6>] lock_sock_nested+0xc6/0x120 net/core/sock.c:2511
 [<ffffffff8341b189>] lock_sock include/net/sock.h:1404 [inline]
 [<ffffffff8341b189>] inet_shutdown+0x69/0x360 net/ipv4/af_inet.c:823
 [<ffffffff836bd340>] pppol2tp_session_close+0xa0/0xe0 net/l2tp/l2tp_ppp.c:441
 [<ffffffff836b6b71>] l2tp_tunnel_closeall+0x231/0x350 net/l2tp/l2tp_core.c:1368
 [<ffffffff836b73f2>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff8301c095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff8128578e>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff8128578e>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff8128578e>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff8128578e>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff8128578e>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff839f9efb>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff81149037>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff81149037>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839f8ae1>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839f8ae1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839f4c70>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  267.748311]  [<ffffffff81edc121>] ? vsnprintf+0x441/0x1840 lib/vsprintf.c:2045
 [<ffffffff81edd66e>] snprintf+0xae/0xe0 lib/vsprintf.c:2177
 [<ffffffff8307045e>] __dev_alloc_name+0x26e/0x310 net/core/dev.c:1065
 [<ffffffff830706bf>] dev_alloc_name_ns net/core/dev.c:1112 [inline]
 [<ffffffff830706bf>] dev_get_valid_name+0xaf/0x160 net/core/dev.c:1127
 [<ffffffff82817694>] tun_set_iff drivers/net/tun.c:1799 [inline]
 [<ffffffff82817694>] __tun_chr_ioctl+0x1e34/0x3450 drivers/net/tun.c:2051
 [<ffffffff82818d0a>] tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2300
 [<ffffffff815b051c>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff815b051c>] file_ioctl fs/ioctl.c:493 [inline]
 [<ffffffff815b051c>] do_vfs_ioctl+0x1ac/0x11a0 fs/ioctl.c:677
 [<ffffffff815b159f>] SYSC_ioctl fs/ioctl.c:694 [inline]
 [<ffffffff815b159f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:685
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f3313>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
------------[ cut here ]------------
BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff836b633c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
PGD 1c3b52067 
PUD 1bc72b067 
PMD 0 

Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 21925 Comm: syz-executor4 Tainted: G        W       4.9.96-g71fce1e #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d75a0000 task.stack: ffff88019a250000
RIP: 0010:[<ffffffff836b633c>]  [<ffffffff836b633c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
RSP: 0018:ffff88019a257ca0  EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8801c1278f00 RCX: ffffc9000116e000
RDX: 1ffff1003766ab50 RSI: ffffffff836b6311 RDI: ffff8801bb355a80
RBP: ffff88019a257cc0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801bb355900
R13: ffff8801c1278f08 R14: 0000000000000000 R15: ffffffff8300ebe0
FS:  00007fc05bb4a700(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001b9349000 CR4: 00000000001606f0
DR0: 0000000020000000 DR1: 0000000020000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 ffff8801d8b01980 ffff8801c1278f00 ffff8801d8b01d50 ffff8801d8b01c58
 ffff88019a257ce8 ffffffff836bdc22 ffff8801d8b01dc0 ffff8801d8b01980
 ffffffff836bdb50 ffff88019a257d20 ffffffff8301c095 ffff8801d8b01dc0
Call Trace:
 [<ffffffff836bdc22>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:297 [inline]
 [<ffffffff836bdc22>] pppol2tp_session_destruct+0xd2/0x110 net/l2tp/l2tp_ppp.c:460
 [<ffffffff8301c095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff83023b23>] sk_destruct+0x63/0x80 net/core/sock.c:1463
 [<ffffffff83023c9e>] __sk_free+0x15e/0x220 net/core/sock.c:1471
 [<ffffffff83023d8b>] sk_free+0x2b/0x40 net/core/sock.c:1482
 [<ffffffff836c0f19>] sock_put include/net/sock.h:1588 [inline]
 [<ffffffff836c0f19>] pppol2tp_release+0x239/0x2e0 net/l2tp/l2tp_ppp.c:501
 [<ffffffff8300eab6>] sock_release+0x96/0x1c0 net/socket.c:599
 [<ffffffff8300ebf6>] sock_close+0x16/0x20 net/socket.c:1046
 [<ffffffff81575b13>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff81576035>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119603c>] task_work_run+0x10c/0x180 kernel/task_work.c:116
 [<ffffffff8100559c>] tracehook_notify_resume include/linux/tracehook.h:191 [inline]
 [<ffffffff8100559c>] exit_to_usermode_loop+0xfc/0x120 arch/x86/entry/common.c:161
 [<ffffffff810064d4>] prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
 [<ffffffff810064d4>] syscall_return_slowpath arch/x86/entry/common.c:260 [inline]
 [<ffffffff810064d4>] do_syscall_64+0x364/0x490 arch/x86/entry/common.c:287
 [<ffffffff839f3313>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
Code: 49 8d bc 24 80 01 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 c6 00 00 00 4d 8b b4 24 80 01 00 00 <f0> 41 ff 8e 80 00 00 00 74 69 e8 b5 66 ca fd 4c 89 ea 48 b8 00 
RIP  [<ffffffff836b633c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
 RSP <ffff88019a257ca0>
CR2: 0000000000000080
---[ end trace 6683cbc6363d38be ]---