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From: Don Zickus <dzickus@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Babu Moger <babu.moger@oracle.com>,
	mingo@kernel.org, ak@linux.intel.com, jkosina@suse.cz,
	baiyaowei@cmss.chinamobile.com, atomlin@redhat.com,
	uobergfe@redhat.com, tj@kernel.org,
	hidehiro.kawai.ez@hitachi.com, johunt@akamai.com,
	davem@davemloft.net, sparclinux@vger.kernel.org,
	linux-kernel@vger.kernel.org, sam@ravnborg.org
Subject: Re: [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi_disable
Date: Fri, 21 Oct 2016 11:11:14 -0400	[thread overview]
Message-ID: <20161021151114.GC35881@redhat.com> (raw)
In-Reply-To: <20161020202527.b01839356c6d34ed0cba3569@linux-foundation.org>

On Thu, Oct 20, 2016 at 08:25:27PM -0700, Andrew Morton wrote:
> On Thu, 20 Oct 2016 12:14:14 -0400 Don Zickus <dzickus@redhat.com> wrote:
> 
> > > > -static int watchdog_nmi_enable(unsigned int cpu) { return 0; }
> > > > -static void watchdog_nmi_disable(unsigned int cpu) { return; }
> > > > +/*
> > > > + * These two functions are mostly architecture specific
> > > > + * defining them as weak here.
> > > > + */
> > > > +int __weak arch_watchdog_nmi_enable(unsigned int cpu) { return 0; }
> > > > +void __weak arch_watchdog_nmi_disable(unsigned int cpu) { return; }
> > > > +
> > > >  #endif /* CONFIG_HARDLOCKUP_DETECTOR */
> > > 
> > > This is a strange way of using __weak.
> > > 
> > > Take a look at (one of many examples) kernel/module.c:module_alloc(). 
> > > We simply provide a default implementation and some other compilation
> > > unit can override (actually replace) that at link time.  No strange
> > > ifdeffing needed.
> > 
> > Yeah, this is mostly because of how we enable the hardlockup detector.
> > 
> > Some arches use the perf hw and enable CONFIG_HARDLOCKUP_DETECTOR.  Other
> > arches just use their own variant of nmi and set CONFIG_HAVE_NMI_WATCHDOG and
> > the rest of the arches do not use this.
> > 
> > So the thought was if CONFIG_HARDLOCKUP_DETECTOR use that implementation,
> > everyone else use the __weak version.  Then the arches like sparc can override
> > the weak version with their own nmi enablement.
> > 
> > I don't know how to represent those 3 states correctly and the above is what
> > we end up with.
> 
> <head spins>
> 
> Is there a suitable site where we could capture these considerations in
> a code comment?

Hi Andrew,

I am not sure I understand your question.  When you say 'site', are you
referring to the kernel/watchdog.c file?

The other approach that might help de-clutter this file, is to pull out the
HARDLOCKUP_DETECTOR changes (as they are arch specific) and move it to say
kernel/watchdog_hw_ld.c.  Then all the nmi hooks in kernel/watchdog.c can be
__weak and overridden by the kernel_watchdog_hw_ld.c file or the sparc
files.

This would leave kernel/watchdog.c with just a framework and the
arch-agnostic softlockup detector.  Probably easier to read and digest.

Thoughts?

Cheers,
Don

  reply	other threads:[~2016-10-21 15:11 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-13 20:38 [PATCH v2 0/2] Introduce arch specific nmi enable, disable handlers Babu Moger
2016-10-13 20:38 ` [PATCH v2 1/2] watchdog: Introduce arch_watchdog_nmi_enable and arch_watchdog_nmi_disable Babu Moger
2016-10-17 17:31   ` Don Zickus
2016-10-18  2:46     ` Babu Moger
2016-10-20  0:00   ` Andrew Morton
2016-10-20 16:14     ` Don Zickus
2016-10-21  3:25       ` Andrew Morton
2016-10-21 15:11         ` Don Zickus [this message]
2016-10-21 19:19           ` Andrew Morton
2016-10-21 21:50             ` Babu Moger
2016-10-24 15:19               ` Don Zickus
2016-10-25  0:55                 ` Babu Moger
2016-10-13 20:38 ` [PATCH v2 2/2] sparc: Implement " Babu Moger
2016-10-17 14:25 ` [PATCH v2 0/2] Introduce arch specific nmi enable, disable handlers Don Zickus

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