linux-kernel - Re: [PATCH 3/5] kernel/watchdog: adapt the watchdog

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Message-ID: <YUK06iqiCwiIvpRM@piliu.users.ipa.redhat.com>
Date:   Thu, 16 Sep 2021 11:07:22 +0800
From:   Pingfan Liu <piliu@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Pingfan Liu <kernelfans@...il.com>, linux-kernel@...r.kernel.org,
        Sumit Garg <sumit.garg@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Julien Thierry <jthierry@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Petr Mladek <pmladek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Wang Qing <wangqing@...o.com>,
        Santosh Sivaraj <santosh@...six.org>
Subject: Re: [PATCH 3/5] kernel/watchdog: adapt the watchdog_hld interface
 for async model

On Wed, Sep 15, 2021 at 04:02:28PM +0200, Peter Zijlstra wrote:
> On Wed, Sep 15, 2021 at 11:51:01AM +0800, 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.
> > 
> > The async model is achieved by introducing an extra parameter notifier
> > of watchdog_nmi_probe().
> > 
> > Note after this patch, the async model, which is utilized by the next
> > patch, does not take effect yet.
> 
> I can't make any sense of what you're trying to do..
> 
Sorry for a bad expression. what I mean is: this patch [3/5] provides an
framework for async model. But since watchdog_nmi_probe() still return 0 or
-ENODEV after this patch, the code's behavior is the same as original.

Does it make sense to you?
> > +static void watchdog_nmi_report_capability(struct watchdog_nmi_status *data)
> > +{
> > +	/* Set status to 1 temporary to block any further access */
> > +	if (atomic_cmpxchg((atomic_t *)&nmi_watchdog_status, -EBUSY, 1)
> > +			== -EBUSY) {
> 
> But this..
> 
Oh, check other codes, for a wrapped condition, blanks should be better choice.
> > +		if (!data->status) {
> > +			nmi_watchdog_status = 0;
> > +			lockup_detector_update_enable();
> > +		} else {
> > +			nmi_watchdog_status = -ENODEV;
> > +			/* turn offf watchdog_enabled forever */
> > +			lockup_detector_update_enable();
> > +			pr_info("Perf NMI watchdog permanently disabled\n");
> > +		}
> > +	}
> > +}
> 
> > @@ -467,7 +494,8 @@ static void watchdog_enable(unsigned int cpu)
> >  	/* Initialize timestamp */
> >  	update_touch_ts();
> >  	/* Enable the perf event */
> > -	if (watchdog_enabled & NMI_WATCHDOG_ENABLED)
> > +	if (watchdog_enabled &
> > +			(NMI_WATCHDOG_ENABLED | NMI_WATCHDOG_UNDETERMINED))
> 
> and this, are horrible indenting.

Ditto.

Thanks for your comment and review.

Regards,

	Pingfan