linux-kernel - Re: 85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() .."): WARNING: CPU: 0 PID: 1 at kernel/kthread.c:486 kthread

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Date:   Thu, 3 May 2018 18:54:52 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     kernel test robot <lkp@...el.com>
Cc:     LKP <lkp@...org>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>, wfg@...ux.intel.com
Subject: Re: 85f1abe001 ("kthread, sched/wait: Fix kthread_parkme() .."):
 WARNING: CPU: 0 PID: 1 at kernel/kthread.c:486 kthread_park

On Thu, May 03, 2018 at 11:52:31PM +0800, kernel test robot wrote:
> [    0.011005] CPU: GenuineIntel Intel Core Processor (Haswell) (family: 0x6, model: 0x3c, stepping: 0x4)
> [    0.012011] Spectre V2 : Spectre mitigation: kernel not compiled with retpoline; no mitigation available!
> [    0.013949] Performance Events: no PMU driver, software events only.
> [    0.019490] NMI watchdog: Perf event create on CPU 0 failed with -2
> [    0.020005] NMI watchdog: Perf NMI watchdog permanently disabled
> [    0.020692] WARNING: CPU: 0 PID: 1 at kernel/kthread.c:486 kthread_park+0x2b/0x56
> [    0.021000] CPU: 0 PID: 1 Comm: swapper Not tainted 4.17.0-rc3-00038-g85f1abe #687
> [    0.021000] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> [    0.021000] EIP: kthread_park+0x2b/0x56
> [    0.021000] EFLAGS: 00210202 CPU: 0
> [    0.021000] EAX: cf464d40 EBX: cf422500 ECX: 00000000 EDX: 00000004
> [    0.021000] ESI: c221e2c0 EDI: 00000000 EBP: cf42df68 ESP: cf42df60
> [    0.021000]  DS: 007b ES: 007b FS: 0000 GS: 00e0 SS: 0068
> [    0.021000] CR0: 80050033 CR2: ffffffff CR3: 022e8000 CR4: 00140690
> [    0.021000] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> [    0.021000] DR6: fffe0ff0 DR7: 00000400
> [    0.021000] Call Trace:
> [    0.021000]  smpboot_update_cpumask_percpu_thread+0x28/0x42
> [    0.021000]  softlockup_update_smpboot_threads+0x37/0x39
> [    0.021000]  lockup_detector_reconfigure+0x17/0x62
> [    0.021000]  lockup_detector_init+0x5d/0x69
> [    0.021000]  kernel_init_freeable+0x52/0x15c
> [    0.021000]  ? rest_init+0xf4/0xf4
> [    0.021000]  kernel_init+0x8/0xd0
> [    0.021000]  ret_from_fork+0x19/0x30
> [    0.021000] Code: 55 89 e5 56 53 8b 50 14 0f ba e2 15 72 02 0f 0b 8b 98 44 03 00 00 80 e2 04 74 09 0f 0b be da ff ff ff eb 2c 8b 13 80 e2 04 74 09 <0f> 0b be f0 ff ff ff eb 1c 80 0b 04 8b 15 70 de f6 c1 31 f6 39 
> [    0.021000] ---[ end trace 3a71adb42feecba7 ]---
> [    0.021060] TSC deadline timer enabled

Clearly my machine didn't do that :-)

I think I see what's going on, this path actually does a kthread_park()
when already parked, which sorta used to work.

Let me try and fix that.