Re: [PATCH 3/5] kernel/watchdog: adapt the watchdog_hld interface for async model

[Petr Mladek]

On Thu 2021-09-16 10:29:05, Petr Mladek wrote:
> On Wed 2021-09-15 11:51:01, Pingfan Liu wrote:
> > When lockup_detector_init()->watchdog_nmi_probe(), PMU may be not ready
> > yet. E.g. on arm64, PMU is not ready until
> > device_initcall(armv8_pmu_driver_init).  And it is deeply integrated
> > with the driver model and cpuhp. Hence it is hard to push this
> > initialization before smp_init().
> > 
> > But it is easy to take an opposite approach by enabling watchdog_hld to
> > get the capability of PMU async.
> 
> This is another cryptic description. I have probably got it after
> looking at the 5th patch (was not Cc :-(
> 
> > The async model is achieved by introducing an extra parameter notifier
> > of watchdog_nmi_probe().
> 
> I would say that the code is horrible and looks too complex.
> 
> What about simply calling watchdog_nmi_probe() and
> lockup_detector_setup() once again when watchdog_nmi_probe()
> failed in lockup_detector_init()?
> 
> Or do not call lockup_detector_init() at all in
> kernel_init_freeable() when PMU is not ready yet.

BTW: It is an overkill to create your own kthread just to run some
code just once. And you implemeted it a wrong way. The kthread
must wait in a loop until someone else stop it and read
the exit code.

The easiest solution is to queue a work into system_wq for this.

I was not Cc for the 5th patch, so I write it here.

Best Regards,
Petr