BUG: sleeping function called from invalid context at net/core/sock.c:2502
in_atomic(): 1, irqs_disabled(): 0, pid: 3879, name: syz-executor2
5 locks held by syz-executor2/3879:
 #0:  (sb_writers#3){.+.+.+}, at: [<ffffffff815e50cf>] sb_start_write include/linux/fs.h:1573 [inline]
 #0:  (sb_writers#3){.+.+.+}, at: [<ffffffff815e50cf>] mnt_want_write+0x3f/0xb0 fs/namespace.c:391
 #1:  (sb_internal){.+.+..}, at: [<ffffffff8175ca65>] sb_start_intwrite include/linux/fs.h:1620 [inline]
 #1:  (sb_internal){.+.+..}, at: [<ffffffff8175ca65>] ext4_evict_inode+0x345/0x1240 fs/ext4/inode.c:240
 #2:  (jbd2_handle){++++..}, at: [<ffffffff81889293>] start_this_handle+0x443/0xe40 fs/jbd2/transaction.c:387
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] spin_trylock include/linux/spinlock.h:312 [inline]
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] ext4_lock_group fs/ext4/ext4.h:2896 [inline]
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] ext4_free_inode+0x77f/0x1360 fs/ext4/ialloc.c:313
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037
Preemption disabled at:[  189.916998] [<ffffffff81737f5f>] spin_trylock include/linux/spinlock.h:312 [inline]
Preemption disabled at:[  189.916998] [<ffffffff81737f5f>] ext4_lock_group fs/ext4/ext4.h:2896 [inline]
Preemption disabled at:[  189.916998] [<ffffffff81737f5f>] ext4_free_inode+0x77f/0x1360 fs/ext4/ialloc.c:313
CPU: 0 PID: 3879 Comm: syz-executor2 Not tainted 4.9.124-g6a1b592 #30
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207cd8 ffffffff81eb95e9 ffffffff81737f5f 0000000000000000
 0000000000000101 ffff8801b84fc800 ffff8801b84fc800 ffff8801db207d10
 ffffffff81426851 ffff8801b84fc800 ffffffff840f88a0 00000000000009c6
Call Trace:
 <IRQ> [  189.968560]  [<ffffffff81eb95e9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  189.968560]  [<ffffffff81eb95e9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81426851>] ___might_sleep.cold.123+0x1bc/0x1f5 kernel/sched/core.c:7988
 [<ffffffff811bd9a5>] __might_sleep+0x95/0x1a0 kernel/sched/core.c:7945
 [<ffffffff8302b774>] lock_sock_nested+0x34/0x120 net/core/sock.c:2502
 [<ffffffff83428dd9>] lock_sock include/net/sock.h:1404 [inline]
 [<ffffffff83428dd9>] inet_shutdown+0x69/0x360 net/ipv4/af_inet.c:823
 [<ffffffff836cb740>] pppol2tp_session_close+0xa0/0xe0 net/l2tp/l2tp_ppp.c:441
 [<ffffffff836c4f71>] l2tp_tunnel_closeall+0x231/0x350 net/l2tp/l2tp_core.c:1368
 [<ffffffff836c57f2>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff830281f5>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff812899ee>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff812899ee>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff812899ee>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff812899ee>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff812899ee>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff83a085c0>] __do_softirq+0x210/0x940 kernel/softirq.c:288
 [<ffffffff8114d554>] invoke_softirq kernel/softirq.c:368 [inline]
 [<ffffffff8114d554>] irq_exit+0x114/0x150 kernel/softirq.c:409
 [<ffffffff83a071a1>] exiting_irq arch/x86/include/asm/apic.h:669 [inline]
 [<ffffffff83a071a1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:962
 [<ffffffff83a03330>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  190.098947]  [<ffffffff8172c175>] ? ext4_inode_bitmap_csum_set+0x85/0x4e0 fs/ext4/bitmap.c:45
 [<ffffffff81738115>] ext4_free_inode+0x935/0x1360 fs/ext4/ialloc.c:327
 [<ffffffff8175d36e>] ext4_evict_inode+0xc4e/0x1240 fs/ext4/inode.c:310
 [<ffffffff815d308e>] evict+0x22e/0x4f0 fs/inode.c:553
 [<ffffffff815d3b21>] iput_final fs/inode.c:1516 [inline]
 [<ffffffff815d3b21>] iput+0x371/0x900 fs/inode.c:1543
 [<ffffffff815af428>] do_unlinkat+0x4f8/0x680 fs/namei.c:4087
 [<ffffffff815b10ea>] SYSC_unlink fs/namei.c:4128 [inline]
 [<ffffffff815b10ea>] SyS_unlink+0x1a/0x20 fs/namei.c:4126
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a019d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

=================================
[ INFO: inconsistent lock state ]
4.9.124-g6a1b592 #30 Tainted: G        W      
---------------------------------
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
syz-executor2/3879 [HC0[0]:SC1[3]:HE1:SE0] takes:
 (sk_lock-AF_PPPOX){+.?.+.}, at: [<ffffffff83428dd9>] lock_sock include/net/sock.h:1404 [inline]
 (sk_lock-AF_PPPOX){+.?.+.}, at: [<ffffffff83428dd9>] 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:190
  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]
  pppol2tp_connect+0xd9/0x18f0 net/l2tp/l2tp_ppp.c:590
  SYSC_connect+0x1b8/0x300 net/socket.c:1575
  SyS_connect+0x24/0x30 net/socket.c:1556
  do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
  entry_SYSCALL_64_after_swapgs+0x5d/0xdb
irq event stamp: 1044732
hardirqs last  enabled at (1044732): [<ffffffff83a02369>] restore_regs_and_iret+0x0/0x1d
hardirqs last disabled at (1044731): [<ffffffff83a0332b>] apic_timer_interrupt+0x9b/0xb0 arch/x86/entry/entry_64.S:648
softirqs last  enabled at (1042746): [<ffffffff83a08825>] __do_softirq+0x475/0x940 kernel/softirq.c:314
softirqs last disabled at (1043711): [<ffffffff8114d554>] invoke_softirq kernel/softirq.c:368 [inline]
softirqs last disabled at (1043711): [<ffffffff8114d554>] irq_exit+0x114/0x150 kernel/softirq.c:409

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 ***

5 locks held by syz-executor2/3879:
 #0:  (sb_writers#3){.+.+.+}, at: [<ffffffff815e50cf>] sb_start_write include/linux/fs.h:1573 [inline]
 #0:  (sb_writers#3){.+.+.+}, at: [<ffffffff815e50cf>] mnt_want_write+0x3f/0xb0 fs/namespace.c:391
 #1:  (sb_internal){.+.+..}, at: [<ffffffff8175ca65>] sb_start_intwrite include/linux/fs.h:1620 [inline]
 #1:  (sb_internal){.+.+..}, at: [<ffffffff8175ca65>] ext4_evict_inode+0x345/0x1240 fs/ext4/inode.c:240
 #2:  (jbd2_handle){++++..}, at: [<ffffffff81889293>] start_this_handle+0x443/0xe40 fs/jbd2/transaction.c:387
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] spin_trylock include/linux/spinlock.h:312 [inline]
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] ext4_lock_group fs/ext4/ext4.h:2896 [inline]
 #3:  (&(&bgl->locks[i].lock)->rlock){+.+...}, at: [<ffffffff81737f5f>] ext4_free_inode+0x77f/0x1360 fs/ext4/ialloc.c:313
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #4:  (rcu_callback){......}, at: [<ffffffff81289ace>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 0 PID: 3879 Comm: syz-executor2 Tainted: G        W       4.9.124-g6a1b592 #30
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db207a58 ffffffff81eb95e9 ffff8801b84fc800 ffffffff85601d90
 ffff8801b84fd190 ffff8801b84fd1b0 0000000000000000 ffff8801db207ac8
 ffffffff81429ccd 0000000000000003 0000000000000001 ffff880100000000
Call Trace:
 <IRQ> [  190.498135]  [<ffffffff81eb95e9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  190.498135]  [<ffffffff81eb95e9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81429ccd>] print_usage_bug.cold.57+0x327/0x421 kernel/locking/lockdep.c:2387
 [<ffffffff81237726>] valid_state kernel/locking/lockdep.c:2400 [inline]
 [<ffffffff81237726>] mark_lock_irq kernel/locking/lockdep.c:2602 [inline]
 [<ffffffff81237726>] mark_lock+0xcc6/0x1280 kernel/locking/lockdep.c:3065
 [<ffffffff812390f0>] mark_irqflags kernel/locking/lockdep.c:2923 [inline]
 [<ffffffff812390f0>] __lock_acquire+0xd40/0x4070 kernel/locking/lockdep.c:3302
 [<ffffffff8123ce90>] lock_acquire+0x130/0x3e0 kernel/locking/lockdep.c:3756
 [<ffffffff8302b806>] lock_sock_nested+0xc6/0x120 net/core/sock.c:2511
 [<ffffffff83428dd9>] lock_sock include/net/sock.h:1404 [inline]
 [<ffffffff83428dd9>] inet_shutdown+0x69/0x360 net/ipv4/af_inet.c:823
 [<ffffffff836cb740>] pppol2tp_session_close+0xa0/0xe0 net/l2tp/l2tp_ppp.c:441
 [<ffffffff836c4f71>] l2tp_tunnel_closeall+0x231/0x350 net/l2tp/l2tp_core.c:1368
 [<ffffffff836c57f2>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff830281f5>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff812899ee>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff812899ee>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff812899ee>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff812899ee>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff812899ee>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff83a085c0>] __do_softirq+0x210/0x940 kernel/softirq.c:288
 [<ffffffff8114d554>] invoke_softirq kernel/softirq.c:368 [inline]
 [<ffffffff8114d554>] irq_exit+0x114/0x150 kernel/softirq.c:409
 [<ffffffff83a071a1>] exiting_irq arch/x86/include/asm/apic.h:669 [inline]
 [<ffffffff83a071a1>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:962
 [<ffffffff83a03330>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  190.669559]  [<ffffffff8172c175>] ? ext4_inode_bitmap_csum_set+0x85/0x4e0 fs/ext4/bitmap.c:45
 [<ffffffff81738115>] ext4_free_inode+0x935/0x1360 fs/ext4/ialloc.c:327
 [<ffffffff8175d36e>] ext4_evict_inode+0xc4e/0x1240 fs/ext4/inode.c:310
 [<ffffffff815d308e>] evict+0x22e/0x4f0 fs/inode.c:553
 [<ffffffff815d3b21>] iput_final fs/inode.c:1516 [inline]
 [<ffffffff815d3b21>] iput+0x371/0x900 fs/inode.c:1543
 [<ffffffff815af428>] do_unlinkat+0x4f8/0x680 fs/namei.c:4087
 [<ffffffff815b10ea>] SYSC_unlink fs/namei.c:4128 [inline]
 [<ffffffff815b10ea>] SyS_unlink+0x1a/0x20 fs/namei.c:4126
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff83a019d3>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
BUG: unable to handle kernel NULL pointer dereference at 0000000000000080
IP: [<ffffffff836c473c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
PGD 196ed8067 [  190.840309] PUD 1ca4bb067 
Oops: 0002 [#1] PREEMPT SMP KASAN
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 12480 Comm: syz-executor0 Tainted: G        W       4.9.124-g6a1b592 #30
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff880196299800 task.stack: ffff88019bb98000
RIP: 0010:[<ffffffff836c473c>]  [<ffffffff836c473c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
RSP: 0018:ffff88019bb9fc98  EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8801d4247400 RCX: 0000000000000000
RDX: 1ffff1003b2945c0 RSI: ffffffff836c4711 RDI: ffff8801d94a2e00
RBP: ffff88019bb9fcb8 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff8801d94a2c80
R13: ffff8801d4247408 R14: 0000000000000000 R15: 0000000000000000
FS:  0000000001bc5940(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000080 CR3: 00000001d3dc9000 CR4: 00000000001606f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff88019c44d500 ffff8801d4247400 ffff88019c44d8d0 ffff88019c44d7d8
 ffff88019bb9fce0 ffffffff836cc022 ffff88019c44d940 ffff88019c44d500
 ffffffff836cbf50 ffff88019bb9fd18 ffffffff830281f5 ffff88019c44d940
Call Trace:
 [<ffffffff836cc022>] l2tp_session_dec_refcount_1 net/l2tp/l2tp_core.h:297 [inline]
 [<ffffffff836cc022>] pppol2tp_session_destruct+0xd2/0x110 net/l2tp/l2tp_ppp.c:460
 [<ffffffff830281f5>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff8302fc83>] sk_destruct+0x63/0x80 net/core/sock.c:1463
 [<ffffffff8302fcef>] __sk_free+0x4f/0x220 net/core/sock.c:1471
 [<ffffffff8302feeb>] sk_free+0x2b/0x40 net/core/sock.c:1482
 [<ffffffff836cf329>] sock_put include/net/sock.h:1588 [inline]
 [<ffffffff836cf329>] pppol2tp_release+0x239/0x2e0 net/l2tp/l2tp_ppp.c:501
 [<ffffffff83018357>] __sock_release+0xd7/0x260 net/socket.c:605
 [<ffffffff830184f9>] sock_close+0x19/0x20 net/socket.c:1059
 [<ffffffff8157ca73>] __fput+0x263/0x700 fs/file_table.c:208
 [<ffffffff8157cf95>] ____fput+0x15/0x20 fs/file_table.c:244
 [<ffffffff8119a66c>] 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
 [<ffffffff83a019d3>] 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 a5 c5 c9 fd 4c 89 ea 48 b8 00 
RIP  [<ffffffff836c473c>] l2tp_session_free+0x11c/0x200 net/l2tp/l2tp_core.c:1765
 RSP <ffff88019bb9fc98>
CR2: 0000000000000080
---[ end trace 86eb7c07a1de7f4b ]---