WARNING: CPU: 3 PID: 3034 at kernel/kthread.c:87 free_kthread_struct+0xa2/0xe0 kernel/kthread.c:87
Kernel panic - not syncing: panic_on_warn set ...

CPU: 3 PID: 3034 Comm: syzkaller985877 Not tainted 4.14.0-rc7-next-20171102+ #9
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
 <IRQ>
 __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:ffff88006df07768 EFLAGS: 00010206
RAX: ffff88003a3443c0 RBX: ffff88006ccc0300 RCX: ffffffff814937d2
RDX: 0000000000000100 RSI: 0000000000000000 RDI: ffff88006ccc0488
RBP: ffff88006df07770 R08: 0000000000000000 R09: 1ffff1000dbe0ed4
R10: ffff88003a3443c0 R11: 0000000000000001 R12: 1ffff1000dbe0ef0
R13: 1ffff1000dbe0ef4 R14: 0000000000000000 R15: ffff88006df077e0
 free_task+0x134/0x1a0 kernel/fork.c:390
 __put_task_struct+0x229/0x3b0 kernel/fork.c:663
 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:2935 [inline]
 __rcu_process_callbacks kernel/rcu/tree.c:2902 [inline]
 rcu_process_callbacks+0xd74/0x17d0 kernel/rcu/tree.c:2919
 __do_softirq+0x29d/0xbb2 kernel/softirq.c:284
 invoke_softirq kernel/softirq.c:364 [inline]
 irq_exit+0x1d3/0x210 kernel/softirq.c:405
 exiting_irq arch/x86/include/asm/apic.h:540 [inline]
 smp_apic_timer_interrupt+0x16b/0x700 arch/x86/kernel/apic/apic.c:1052
 apic_timer_interrupt+0x9d/0xb0 arch/x86/entry/entry_64.S:577
 </IRQ>
RIP: 0010:arch_local_irq_restore arch/x86/include/asm/paravirt.h:777 [inline]
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:160 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x5e/0xba kernel/locking/spinlock.c:189
RSP: 0018:ffff880039c9fa68 EFLAGS: 00000286 ORIG_RAX: ffffffffffffff11
RAX: dffffc0000000000 RBX: 0000000000000286 RCX: 0000000000000000
RDX: 1ffffffff0bd9671 RSI: 0000000000000001 RDI: 0000000000000286
RBP: ffff880039c9fa78 R08: ffff880039cafe00 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88006df1d5c0
R13: ffff88006df1d5c0 R14: ffff88006df1d680 R15: ffff880039c9fe00
 unlock_hrtimer_base kernel/time/hrtimer.c:776 [inline]
 hrtimer_start_range_ns+0x6b1/0xee0 kernel/time/hrtimer.c:980
 hrtimer_start_expires include/linux/hrtimer.h:391 [inline]
 do_nanosleep+0x1c6/0x6e0 kernel/time/hrtimer.c:1470
 hrtimer_nanosleep+0x2b2/0x860 kernel/time/hrtimer.c:1527
 SYSC_nanosleep kernel/time/hrtimer.c:1559 [inline]
 SyS_nanosleep+0x175/0x1f0 kernel/time/hrtimer.c:1546
 entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x439820
RSP: 002b:00007ffeef5eb1e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 0000000000001530 RCX: 0000000000439820
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffeef5eb1f0
RBP: 0000000000000086 R08: 0000000000000bda R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffeef5eb1c0
R13: 0000000000001530 R14: 0000000000407360 R15: 0000000000000000
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..