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SubjectRe: [RFC PATCH v2 13/14] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter
On Tue, Mar 26, 2019 at 10:29:52PM +0100, Thomas Gleixner wrote:
> On Wed, 27 Feb 2019, Ricardo Neri wrote:
> > + When hpet is specified, the NMI watchdog will be driven
> > + by an HPET timer, if available in the system. Otherwise,
> > + the perf-based implementation will be used. Specifying
> > + hpet implies that nmi_watchdog is on.
>
> How so?
>
I meant to say that the user does not need to provide nmi_watchdog=1 and
nmi_watchdog=hpet separately.

I think this is true because watchdog_user_enabled in kernel/watchdog.c is set
to 1 when CONFIG_HARDLOCKUP_DETECTOR is selected. Also, if nmi_watchdog_available
is set to true if watchdog_nmi_probe() is successful.

Perhaps I can add a warning in case nmi_watchdog=hpet and either
CONFIG_HARDLOCKUP_DETECTOR or CONFIG_HARDLOCKUP_DETECTOR_HPET are not
selected?

> > +static int __init hardlockup_detector_hpet_setup(char *str)
> > +{
> > + if (strstr(str, "hpet"))
> > + hardlockup_use_hpet = true;
>
> strstr()? Not really.

Is strncmp(str, "hpet", 5) more acceptable?

>
> > +
> > + return 0;
> > +}
> > +__setup("nmi_watchdog=", hardlockup_detector_hpet_setup);
> > +
> > /**
> > * hardlockup_detector_hpet_init() - Initialize the hardlockup detector
> > *
> > @@ -405,6 +422,9 @@ int __init hardlockup_detector_hpet_init(void)
> > {
> > int ret;
> >
> > + if (!hardlockup_use_hpet)
> > + return -ENODEV;
>
> This should have been there in the patch which introduces
> hardlockup_detector_hpet_init(). And this patch merily adds the command
> line magic which sets that flag.

Sure, I will move this check into the patch that introduces
hardlockup_detector_hpet_init().

>
> > +
> > if (!is_hpet_enabled())
> > return -ENODEV;
> >
> > diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> > index 367aa81294ef..28cad7310378 100644
> > --- a/kernel/watchdog.c
> > +++ b/kernel/watchdog.c
> > @@ -78,7 +78,7 @@ static int __init hardlockup_panic_setup(char *str)
> > nmi_watchdog_user_enabled = 0;
> > else if (!strncmp(str, "1", 1))
> > nmi_watchdog_user_enabled = 1;
> > - return 1;
> > + return 0;
>
> Why?

My understanding is that this is needed so that other __setup functions that also
want to check "nmi_watchdog" are able to do it. Is this understanding
not correct?

Thanks and BR,
Ricardo

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