IPv4: Oversized IP packet from 127.0.0.1

===============================
[ INFO: suspicious RCU usage. ]
4.9.113-g47bbcd6 #62 Not tainted
-------------------------------
kernel/rcu/tree_plugin.h:678 Illegal synchronize_rcu() in RCU read-side critical section!

other info that might help us debug this:

IPv4: Oversized IP packet from 127.0.0.1

rcu_scheduler_active = 2, debug_locks = 0
6 locks held by syz-executor1/8168:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d81ec>] __fdget_pos+0xac/0xd0 fs/file.c:781
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff81572cce>] file_start_write include/linux/fs.h:2640 [inline]
 #1:  (sb_writers#3){.+.+.+}, at: [<ffffffff81572cce>] vfs_write+0x3ae/0x530 fs/read_write.c:556
 #2:  (&sb->s_type->i_mutex_key#9){++++++}, at: [<ffffffff8172ce92>] inode_lock include/linux/fs.h:766 [inline]
 #2:  (&sb->s_type->i_mutex_key#9){++++++}, at: [<ffffffff8172ce92>] ext4_file_write_iter+0x122/0xd90 fs/ext4/file.c:100
 #3:  (jbd2_handle){++++..}, at: [<ffffffff81884533>] start_this_handle+0x443/0xe40 fs/jbd2/transaction.c:387
 #4:  (rcu_read_lock){......}, at: [<ffffffff81438be0>] find_get_entry+0x0/0x540 include/linux/compiler.h:243
 #5:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #5:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #5:  (rcu_callback){......}, at: [<ffffffff812878ae>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #5:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #5:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 1 PID: 8168 Comm: syz-executor1 Not tainted 4.9.113-g47bbcd6 #62
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb32a9 ffff8801d0233000 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff8801baf028d8 ffff8801db307d90
 ffffffff814260f0 ffff8801baf02780 ffff8801cde32a48 ffff8801cde32248
Call Trace:
 <IRQ> [   99.569228]  [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [   99.569228]  [<ffffffff81eb32a9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff814260f0>] lockdep_rcu_suspicious.cold.48+0x110/0x141 kernel/locking/lockdep.c:4455
 [<ffffffff81284148>] synchronize_rcu+0x68/0x90 kernel/rcu/tree_plugin.h:675
 [<ffffffff836bd17a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bd507>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bddc2>] l2tp_tunnel_destruct+0x2f2/0x590 net/l2tp/l2tp_core.c:1324
 [<ffffffff83021095>] __sk_destruct+0x55/0x590 net/core/sock.c:1428
 [<ffffffff812877ce>] __rcu_reclaim kernel/rcu/rcu.h:118 [inline]
 [<ffffffff812877ce>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 [<ffffffff812877ce>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 [<ffffffff812877ce>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 [<ffffffff812877ce>] rcu_process_callbacks+0x8ae/0x12b0 kernel/rcu/tree.c:3037
 [<ffffffff83a00b7b>] __do_softirq+0x20b/0x937 kernel/softirq.c:284
 [<ffffffff8114b287>] invoke_softirq kernel/softirq.c:364 [inline]
 [<ffffffff8114b287>] irq_exit+0x147/0x190 kernel/softirq.c:405
 [<ffffffff839ff761>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff761>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fb8f0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [   99.682707]  [<ffffffff81f1ad0b>] ? check_preemption_disabled+0x3b/0x170 lib/smp_processor_id.c:51
 [<ffffffff81438f8e>] rcu_read_lock include/linux/rcupdate.h:876 [inline]
 [<ffffffff81438f8e>] find_get_entry+0x3ae/0x540 mm/filemap.c:1092
 [<ffffffff8143a05b>] pagecache_get_page+0x4b/0x720 mm/filemap.c:1203
 [<ffffffff81623fe2>] find_get_page_flags include/linux/pagemap.h:264 [inline]
 [<ffffffff81623fe2>] __find_get_block_slow+0xc2/0x330 fs/buffer.c:212
 [<ffffffff81624280>] unmap_underlying_metadata+0x30/0x100 fs/buffer.c:1629
 [<ffffffff8162a321>] __block_write_begin_int+0x731/0x1040 fs/buffer.c:1995
 [<ffffffff8162ac60>] __block_write_begin+0x30/0x40 fs/buffer.c:2038
 [<ffffffff81756c2d>] ext4_da_write_begin+0x2ed/0x1020 fs/ext4/inode.c:3004
 [<ffffffff81435dc1>] generic_perform_write+0x301/0x510 mm/filemap.c:2740
 [<ffffffff8143d852>] __generic_file_write_iter+0x352/0x540 mm/filemap.c:2865
 [<ffffffff8172d1d3>] ext4_file_write_iter+0x463/0xd90 fs/ext4/file.c:165
 [<ffffffff8156ecb0>] new_sync_write fs/read_write.c:496 [inline]
 [<ffffffff8156ecb0>] __vfs_write+0x3e0/0x580 fs/read_write.c:509
 [<ffffffff81572aa7>] vfs_write+0x187/0x530 fs/read_write.c:557
 [<ffffffff815768d9>] SYSC_write fs/read_write.c:604 [inline]
 [<ffffffff815768d9>] SyS_write+0xd9/0x1c0 fs/read_write.c:596
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839f9f93>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801d7ab0000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 8168 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 8168 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329