Re: [RFC PATCH v2 13/14] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter

From: Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@suse.de>,
	Ashok Raj <ashok.raj@intel.com>,
	Andi Kleen <andi.kleen@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	Ricardo Neri <ricardo.neri@intel.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Tony Luck <tony.luck@intel.com>,
	Clemens Ladisch <clemens@ladisch.de>,
	Arnd Bergmann <arnd@arndb.de>,
	Philippe Ombredanne <pombredanne@nexb.com>,
	Kate Stewart <kstewart@linuxfoundation.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Mimi Zohar <zohar@linux.ibm.com>,
	Jan Kiszka <jan.kiszka@siemens.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	Masahiro Yamada <yamada.masahiro@socionext.com>,
	Nayna Jain <nayna@linux.ibm.com>
Subject: Re: [RFC PATCH v2 13/14] watchdog/hardlockup/hpet: Only enable the HPET watchdog via a boot parameter
Date: Mon, 8 Apr 2019 19:07:28 -0700	[thread overview]
Message-ID: <20190409020728.GA7259@ranerica-svr.sc.intel.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1903262223330.1789@nanos.tec.linutronix.de>

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