===============================
[ INFO: suspicious RCU usage. ]
4.9.113-g9905591 #14 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:


rcu_scheduler_active = 2, debug_locks = 0
2 locks held by udevd/2041:
 #0:  (rcu_read_lock){......}, at: [<ffffffff815c86a2>] __d_lookup+0x42/0x670 fs/dcache.c:2276
 #1:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_reclaim kernel/rcu/rcu.h:108 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_do_batch kernel/rcu/tree.c:2789 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812878ae>] invoke_rcu_callbacks kernel/rcu/tree.c:3053 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812878ae>] __rcu_process_callbacks kernel/rcu/tree.c:3020 [inline]
 #1:  (rcu_callback){......}, at: [<ffffffff812878ae>] rcu_process_callbacks+0x98e/0x12b0 kernel/rcu/tree.c:3037

stack backtrace:
CPU: 1 PID: 2041 Comm: udevd Not tainted 4.9.113-g9905591 #14
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801db307d60 ffffffff81eb32a9 ffff8801ccac4800 0000000000000000
 0000000000000002 ffffffff83c6df20 ffff88019cbc92d8 ffff8801db307d90
 ffffffff814260f0 ffff88019cbc9180 ffff8801cf372a48 ffff8801cf372248
Call Trace:
 <IRQ> [  397.553617]  [<ffffffff81eb32a9>] __dump_stack lib/dump_stack.c:15 [inline]
 <IRQ> [  397.553617]  [<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
 [<ffffffff836bd37a>] __l2tp_session_unhash+0x38a/0x520 net/l2tp/l2tp_core.c:1796
 [<ffffffff836bd707>] l2tp_tunnel_closeall+0x1f7/0x350 net/l2tp/l2tp_core.c:1364
 [<ffffffff836bdfc2>] 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
 [<ffffffff83a00d7b>] __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
 [<ffffffff839ff961>] exiting_irq arch/x86/include/asm/apic.h:659 [inline]
 [<ffffffff839ff961>] smp_apic_timer_interrupt+0x81/0xa0 arch/x86/kernel/apic/apic.c:960
 [<ffffffff839fbaf0>] apic_timer_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:648
 <EOI> [  397.667671]  [<ffffffff81f1ae49>] ? debug_smp_processor_id+0x9/0x20 lib/smp_processor_id.c:56
 [<ffffffff81f1ae49>] debug_smp_processor_id+0x9/0x20 lib/smp_processor_id.c:56
 [<ffffffff8127f645>] __rcu_is_watching kernel/rcu/tree.c:1053 [inline]
 [<ffffffff8127f645>] rcu_is_watching+0x15/0xa0 kernel/rcu/tree.c:1067
 [<ffffffff815c8abf>] rcu_read_unlock include/linux/rcupdate.h:927 [inline]
 [<ffffffff815c8abf>] __d_lookup+0x45f/0x670 fs/dcache.c:2325
 [<ffffffff8159e267>] lookup_fast+0x687/0xf50 fs/namei.c:1611
 [<ffffffff815a0d16>] walk_component+0xf6/0x1bb0 fs/namei.c:1780
 [<ffffffff815a3059>] link_path_walk+0x889/0x1200 fs/namei.c:2120
 [<ffffffff815a3cc4>] path_lookupat.isra.41+0x1b4/0x410 fs/namei.c:2282
 [<ffffffff815a9747>] filename_lookup.part.55+0x177/0x370 fs/namei.c:2317
 [<ffffffff815a9b03>] filename_lookup fs/namei.c:2310 [inline]
 [<ffffffff815a9b03>] user_path_at_empty+0x53/0x70 fs/namei.c:2578
 [<ffffffff81580ae6>] user_path_at include/linux/namei.h:55 [inline]
 [<ffffffff81580ae6>] vfs_fstatat+0xc6/0x170 fs/stat.c:106
 [<ffffffff81581c96>] vfs_stat fs/stat.c:123 [inline]
 [<ffffffff81581c96>] SYSC_newstat+0x86/0xf0 fs/stat.c:270
 [<ffffffff8158209d>] SyS_newstat+0x1d/0x30 fs/stat.c:266
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff839fa193>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb
ODEBUG: object ffff8801db307ce8 is NOT on stack ffff8801ccb28000, but annotated
------------[ cut here ]------------
WARNING: CPU: 1 PID: 2041 at lib/debugobjects.c:303 debug_object_is_on_stack lib/debugobjects.c:303 [inline]
WARNING: CPU: 1 PID: 2041 at lib/debugobjects.c:303 __debug_object_init.cold.10+0x6b/0x2b0 lib/debugobjects.c:329