WARNING: CPU: 1 PID: 21 at net/kcm/kcmsock.c:1992 kcm_exit_net+0x317/0x360 net/kcm/kcmsock.c:1992
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 21 Comm: kworker/u4:1 Not tainted 4.15.0-rc2+ #154
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:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1dc/0x200 kernel/panic.c:547
 report_bug+0x211/0x2d0 lib/bug.c:184
 fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:177
 fixup_bug arch/x86/kernel/traps.c:246 [inline]
 do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:295
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:314
 invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:930
RIP: 0010:kcm_exit_net+0x317/0x360 net/kcm/kcmsock.c:1992
RSP: 0018:ffff8801d9ce7198 EFLAGS: 00010293
RAX: ffff8801d9cdc580 RBX: 1ffff1003b39ce33 RCX: ffffffff84ab6437
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000282
RBP: ffff8801d9ce7260 R08: 0000000000000003 R09: 1ffff1003b39ce0c
R10: ffff8801d9cdc580 R11: 0000000000000003 R12: 1ffff1003b39ce37
R13: ffff8801d9ce7238 R14: ffff8801cd432620 R15: ffff8801ce9ed900
 ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:142
 cleanup_net+0x5c7/0xb60 net/core/net_namespace.c:484
 process_one_work+0xbfd/0x1be0 kernel/workqueue.c:2112
 worker_thread+0x223/0x1990 kernel/workqueue.c:2246
 kthread+0x37a/0x440 kernel/kthread.c:238
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:441
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..