linux-kernel - Re: [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog

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Date:   Fri, 16 Apr 2021 22:10:51 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     linux-kernel@...r.kernel.org, john.stultz@...aro.org,
        sboyd@...nel.org, corbet@....net, Mark.Rutland@....com,
        maz@...nel.org, kernel-team@...com, neeraju@...eaurora.org,
        ak@...ux.intel.com, "Paul E. McKenney" <paulmck@...nel.org>,
        Chris Mason <clm@...com>
Subject: Re: [PATCH v8 clocksource 1/5] clocksource: Provide module parameters to inject delays in watchdog

On Tue, Apr 13 2021 at 21:35, Paul E. McKenney wrote:
>  
> +static int inject_delay_freq;
> +module_param(inject_delay_freq, int, 0644);
> +static int inject_delay_run = 1;
> +module_param(inject_delay_run, int, 0644);

int? Can't we just make them 'unsigned int'? Negative values are not
that useful.

> +static int max_read_retries = 3;
> +module_param(max_read_retries, int, 0644);

max_read_retries is unused here. Should be in the patch which actually
uses it.

> +static void clocksource_watchdog_inject_delay(void)
> +{
> +	int i;
> +	static int injectfail = -1;
> +
> +	if (inject_delay_freq <= 0 || inject_delay_run <= 0)
> +		return;
> +	if (injectfail < 0 || injectfail > INT_MAX / 2)
> +		injectfail = inject_delay_run;
> +	if (!(++injectfail / inject_delay_run % inject_delay_freq)) {

Operator precedence based cleverness is really easy to parse - NOT!

> +		pr_warn("%s(): Injecting delay.\n", __func__);
> +		for (i = 0; i < 2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC; i++)
> +			udelay(1000);
> +		pr_warn("%s(): Done injecting delay.\n", __func__);
> +	}
> +
> +	WARN_ON_ONCE(injectfail < 0);
> +}

Brain melt stage reached by now.

        static unsigned int invocations, injections;

        if (!inject_delay_period || !inject_delay_repeat)
        	return;

        if (!(invocations % inject_delay_period)) {
        	mdelay(2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC);
                if (++injections < inject_delay_repeat)
                	return;
                injections = 0;
        }

        invocations++;
}

Hmm?

Thanks,

        tglx