===============================
[ INFO: suspicious RCU usage. ]
4.9.153+ #18 Not tainted
-------------------------------
net/ipv6/ip6_fib.c:1470 suspicious rcu_dereference_protected() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 0
4 locks held by ksoftirqd/1/17:
 #0:  (((&net->ipv6.ip6_fib_timer))){+.-...}, at: [<ffffffff812622ee>] lockdep_copy_map include/linux/lockdep.h:165 [inline]
 #0:  (((&net->ipv6.ip6_fib_timer))){+.-...}, at: [<ffffffff812622ee>] call_timer_fn+0xde/0x6d0 kernel/time/timer.c:1309
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-...}, at: [<ffffffff826ee9f2>] spin_lock_bh include/linux/spinlock.h:307 [inline]
 #1:  (&(&net->ipv6.fib6_gc_lock)->rlock){+.-...}, at: [<ffffffff826ee9f2>] fib6_run_gc+0xa2/0x2e0 net/ipv6/ip6_fib.c:1816
 #2:  (rcu_read_lock){......}, at: [<ffffffff826e6200>] __fib6_clean_all+0x0/0x230 net/ipv6/ip6_fib.c:1703
 #3:  (&tb->tb6_lock){++--..}, at: [<ffffffff826e62e3>] __fib6_clean_all+0xe3/0x230 net/ipv6/ip6_fib.c:1717

stack backtrace:
CPU: 1 PID: 17 Comm: ksoftirqd/1 Not tainted 4.9.153+ #18
 ffff8801da70f5f0 ffffffff81b47491 ffff8801d2407500 0000000000000000
 0000000000000002 00000000000005be ffff8801da6f2f80 ffff8801da70f620
 ffffffff813feb85 ffff8801da70f840 dffffc0000000000 00000000ffffffff
Call Trace:
 [<ffffffff81b47491>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81b47491>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff813feb85>] lockdep_rcu_suspicious.cold+0x10a/0x149 kernel/locking/lockdep.c:4455
 [<ffffffff826ee14f>] fib6_del+0x81f/0xb20 net/ipv6/ip6_fib.c:1470
 [<ffffffff826ee6ec>] fib6_clean_node+0x29c/0x4d0 net/ipv6/ip6_fib.c:1657
 [<ffffffff826e5ad0>] fib6_walk_continue+0x3e0/0x630 net/ipv6/ip6_fib.c:1583
 [<ffffffff826e608d>] fib6_walk+0x9d/0xf0 net/ipv6/ip6_fib.c:1628
 [<ffffffff826e61c7>] fib6_clean_tree+0xe7/0x120 net/ipv6/ip6_fib.c:1702
 [<ffffffff826e62fb>] __fib6_clean_all+0xfb/0x230 net/ipv6/ip6_fib.c:1718
 [<ffffffff826eea74>] fib6_clean_all net/ipv6/ip6_fib.c:1729 [inline]
 [<ffffffff826eea74>] fib6_run_gc+0x124/0x2e0 net/ipv6/ip6_fib.c:1826
 [<ffffffff826eec4d>] fib6_gc_timer_cb+0x1d/0x30 net/ipv6/ip6_fib.c:1841
 [<ffffffff81262377>] call_timer_fn+0x167/0x6d0 kernel/time/timer.c:1319
 [<ffffffff81262b3b>] expire_timers+0x25b/0x5c0 kernel/time/timer.c:1359
 [<ffffffff8126309f>] __run_timers kernel/time/timer.c:1674 [inline]
 [<ffffffff8126309f>] run_timer_softirq+0x1ff/0x620 kernel/time/timer.c:1687
 [<ffffffff8281b67d>] __do_softirq+0x22d/0x964 kernel/softirq.c:288
 [<ffffffff810ee890>] run_ksoftirqd+0x30/0x60 kernel/softirq.c:680
 [<ffffffff8114d00d>] smpboot_thread_fn+0x5fd/0x950 kernel/smpboot.c:163
 [<ffffffff81141e18>] kthread+0x278/0x310 kernel/kthread.c:211
 [<ffffffff8281645c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
TCP: request_sock_TCPv6: Possible SYN flooding on port 20002. Dropping request.  Check SNMP counters.