linux-kernel - Re: [PATCH RFC clocksource 2/5] clocksource: Retry clock read if long delays detected

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Message-ID: <edbe9ac5fc3f76601f752ce2c5a8052dc05fd4f6.camel@fb.com>
Date:   Wed, 06 Jan 2021 11:28:00 -0500
From:   Rik van Riel <riel@...com>
To:     <paulmck@...nel.org>, <linux-kernel@...r.kernel.org>
CC:     <kernel-team@...com>, John Stultz <john.stultz@...aro.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        "Jonathan Corbet" <corbet@....net>,
        Mark Rutland <Mark.Rutland@....com>,
        Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH RFC clocksource 2/5] clocksource: Retry clock read if
 long delays detected

On Tue, 2021-01-05 at 16:41 -0800, paulmck@...nel.org wrote:
> 
> @@ -203,7 +204,6 @@ static void
> clocksource_watchdog_inject_delay(void)
>  		injectfail = inject_delay_run;
>  	if (!(++injectfail / inject_delay_run % inject_delay_freq)) {
>  		printk("%s(): Injecting delay.\n", __func__);
> -		injectfail = 0;
>  		for (i = 0; i < 2 * WATCHDOG_THRESHOLD / NSEC_PER_MSEC;
> i++)
>  			udelay(1000);

Wait, patch 1 just added that line?

Should patch 1 not add it and this
patch go without
this removal? :)

+               wdagain_nsec = clocksource_cyc2ns(delta, watchdog-
>mult, watchdog->shift);
+               if (wdagain_nsec < 0 || wdagain_nsec >
WATCHDOG_MAX_SKEW) {
+                       wderr_nsec = wdagain_nsec;
+                       if (nretries++ < max_read_retries)
+                               goto retry;
+               }

Given that clocksource_cyc2ns uses unsigned multiplication
followed by a right shift, do we need to test for <0?