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refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 8738 at lib/refcount.c:190 refcount_sub_and_test_checked lib/refcount.c:190 [inline]
WARNING: CPU: 0 PID: 8738 at lib/refcount.c:190 refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 8738 Comm: kworker/u4:6 Not tainted 5.2.0-rc1+ #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x2cb/0x744 kernel/panic.c:219
 __warn.cold+0x20/0x4d kernel/panic.c:576
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:179 [inline]
 fixup_bug arch/x86/kernel/traps.c:174 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:272
 do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:291
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:986
RIP: 0010:refcount_sub_and_test_checked lib/refcount.c:190 [inline]
RIP: 0010:refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180
Code: 1d f3 8f 48 06 31 ff 89 de e8 2c 75 3c fe 84 db 75 94 e8 e3 73 3c fe 48 c7 c7 80 95 a4 87 c6 05 d3 8f 48 06 01 e8 4e b9 0e fe <0f> 0b e9 75 ff ff ff e8 c4 73 3c fe e9 6e ff ff ff 48 89 df e8 47
RSP: 0018:ffff888065a77088 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff815ac7e6 RDI: ffffed100cb4ee03
RBP: ffff888065a77120 R08: ffff88809140a540 R09: ffffed1015d040f1
R10: ffffed1015d040f0 R11: ffff8880ae820787 R12: 00000000ffffffff
R13: 0000000000000001 R14: ffff888065a770f8 R15: 0000000000000000
 refcount_dec_and_test_checked+0x1b/0x20 lib/refcount.c:220
 fib6_info_release include/net/ip6_fib.h:299 [inline]
 fib6_info_release include/net/ip6_fib.h:297 [inline]
 fib6_drop_pcpu_from net/ipv6/ip6_fib.c:926 [inline]
 fib6_purge_rt+0x1d2/0x5e0 net/ipv6/ip6_fib.c:937
 fib6_del_route net/ipv6/ip6_fib.c:1820 [inline]
 fib6_del+0x9bd/0xeb0 net/ipv6/ip6_fib.c:1851
 fib6_clean_node+0x3a5/0x590 net/ipv6/ip6_fib.c:2013
 fib6_walk_continue+0x4a9/0x8e0 net/ipv6/ip6_fib.c:1935
 fib6_walk+0x9d/0x100 net/ipv6/ip6_fib.c:1983
 fib6_clean_tree+0xe0/0x120 net/ipv6/ip6_fib.c:2062
 __fib6_clean_all+0x118/0x2a0 net/ipv6/ip6_fib.c:2078
 fib6_clean_all+0x2b/0x40 net/ipv6/ip6_fib.c:2089
 rt6_sync_down_dev+0x134/0x150 net/ipv6/route.c:4163
 rt6_disable_ip+0x27/0x5f0 net/ipv6/route.c:4168
 addrconf_ifdown+0xa2/0x1220 net/ipv6/addrconf.c:3709
 addrconf_notify+0x5db/0x2270 net/ipv6/addrconf.c:3634
 notifier_call_chain+0xc2/0x230 kernel/notifier.c:95
 __raw_notifier_call_chain kernel/notifier.c:396 [inline]
 raw_notifier_call_chain+0x2e/0x40 kernel/notifier.c:403
 call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1753
 call_netdevice_notifiers_extack net/core/dev.c:1765 [inline]
 call_netdevice_notifiers net/core/dev.c:1779 [inline]
 dev_close_many+0x33f/0x6f0 net/core/dev.c:1522
 rollback_registered_many+0x43b/0xfc0 net/core/dev.c:8193
 unregister_netdevice_many.part.0+0x1b/0x1f0 net/core/dev.c:9324
 unregister_netdevice_many+0x3b/0x50 net/core/dev.c:9323
 ip_tunnel_delete_nets+0x41e/0x5f0 net/ipv4/ip_tunnel.c:1126
 ipgre_exit_batch_net+0x23/0x30 net/ipv4/ip_gre.c:998
 ops_exit_list.isra.0+0xfc/0x150 net/core/net_namespace.c:157
 cleanup_net+0x3fb/0x960 net/core/net_namespace.c:553
 process_one_work+0x989/0x1790 kernel/workqueue.c:2269
 worker_thread+0x98/0xe40 kernel/workqueue.c:2415
 kthread+0x354/0x420 kernel/kthread.c:255
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..