WARNING: CPU: 1 PID: 16 at kernel/kthread.c:87 free_kthread_struct+0xa2/0xe0 kernel/kthread.c:87
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 4.14.0-rc5-mm1+ #20
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:16 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:52
 panic+0x1e4/0x41c kernel/panic.c:183
 __warn+0x1c4/0x1e0 kernel/panic.c:546
 report_bug+0x211/0x2d0 lib/bug.c:183
 fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:177
 do_trap_no_signal arch/x86/kernel/traps.c:211 [inline]
 do_trap+0x260/0x390 arch/x86/kernel/traps.c:260
 do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:297
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:310
 invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:905
RIP: 0010:free_kthread_struct+0xa2/0xe0 kernel/kthread.c:87
RSP: 0018:ffff8801d9f9f730 EFLAGS: 00010206
RAX: ffff8801d9f90440 RBX: ffff8801c8e0be00 RCX: ffffffff8148d7e2
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffff8801c8e0beb8
RBP: ffff8801d9f9f738 R08: 0000000000000001 R09: 1ffff1003b3f3ed5
R10: ffff8801d9f9f670 R11: 0000000000000001 R12: 1ffff1003b3f3ee9
R13: 1ffff1003b3f3eed R14: 0000000000000000 R15: ffff8801d9f9f7a8
 free_task+0x134/0x1a0 kernel/fork.c:390
 __put_task_struct+0x229/0x3b0 kernel/fork.c:668
 put_task_struct include/linux/sched/task.h:95 [inline]
 delayed_put_task_struct+0xca/0x3d0 kernel/exit.c:180
 __rcu_reclaim kernel/rcu/rcu.h:172 [inline]
 rcu_do_batch kernel/rcu/tree.c:2676 [inline]
 invoke_rcu_callbacks kernel/rcu/tree.c:2930 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2897 [inline]
 rcu_process_callbacks+0xd74/0x17d0 kernel/rcu/tree.c:2914
 __do_softirq+0x2d7/0xb85 kernel/softirq.c:284
 run_ksoftirqd+0x50/0x100 kernel/softirq.c:666
 smpboot_thread_fn+0x450/0x7c0 kernel/smpboot.c:164
 kthread+0x38b/0x470 kernel/kthread.c:242
 ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:431
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..