linux-kernel - Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against wakeup

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Message-ID: <1ebda1e3-dae3-9e86-ad92-e1acdead23be@codeaurora.org>
Date:   Thu, 7 Jun 2018 14:00:53 +0530
From:   "Kohli, Gaurav" <gkohli@...eaurora.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>
Cc:     tglx@...utronix.de, mpe@...erman.id.au, mingo@...nel.org,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Neeraj Upadhyay <neeraju@...eaurora.org>,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v1] kthread/smpboot: Serialize kthread parking against
 wakeup

HI ,

In the latest patch mentioned, k should be their instead of p:

-WARN_ON_ONCE(!wait_task_inactive(p, TASK_PARKED))
+WARN_ON_ONCE(!wait_task_inactive(k, TASK_PARKED))

Regards
Gaurav

On 6/7/2018 12:29 AM, Peter Zijlstra wrote:
> On Wed, Jun 06, 2018 at 03:51:16PM +0200, Oleg Nesterov wrote:
>> IIUC, this will only affect smpboot_update_cpumask_percpu_thread() which can hit
>> an already parked thread, but it doesn't need to wait.
>>
>> And it seems that smpboot_update_cpumask_percpu_thread() in turn needs some cleanups.
>> Hmm. and its single user: kernel/watchdog.c.
>>
>> And speaking of watchdog.c, can't we simply kill the "watchdog/%u" threads? This is
>> off-topic, but can't watchdog_timer_fn() use stop_one_cpu_nowait(watchdog) ?
>>
>> And I really think we should unexport kthread_park/unpark(), only smpboot_thread_fn()
>> should use them. kthread() should not play with __kthread_parkme(). And even
>> KTHREAD_SHOULD_PARK must die, I mean it should live in struct smp_hotplug_thread,
>> not in struct kthread.
>>
>> OK, this is off-topic too.
> 
>> And, let me repeat, can't we avoid complete_all() ?
> 
> Yes, or at least if that watchdog crap is the only user.
> 
> I have most of the patch reworking watchdog.c to use stop_one_cpu*(),
> and that cleans up lots -- of course, I've not tested it yet, so it
> could also be breaking lots :-)
> 

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