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

[Kohli, Gaurav]

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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