linux-kernel - Re: [PATCH 2/6] [watchdog] convert touch_softlockup_watchdog to touch

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Date:	Wed, 21 Apr 2010 23:46:12 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Don Zickus <dzickus@...hat.com>
Cc:	mingo@...e.hu, peterz@...radead.org, gorcunov@...il.com,
	aris@...hat.com, linux-kernel@...r.kernel.org,
	randy.dunlap@...cle.com
Subject: Re: [PATCH 2/6] [watchdog] convert touch_softlockup_watchdog to
	touch_watchdog

On Wed, Apr 21, 2010 at 05:31:42PM -0400, Don Zickus wrote:
> On Wed, Apr 21, 2010 at 10:46:01PM +0200, Frederic Weisbecker wrote:
> > On Tue, Apr 20, 2010 at 11:23:59AM -0400, Don Zickus wrote:
> > > Just a scripted conversion to remove touch_softlockup_watchdog.
> > > 
> > > Also converts the once case of touch_all_softlockup_watchdogs to
> > > touch_all_watchdogs.
> > > 
> > > This is done as part of the removal of the old softlockup code and
> > > transition to the new softlockup code.
> > > 
> > > Signed-off-by: Don Zickus <dzickus@...hat.com>
> > 
> > 
> > In fact I worry a bit about this unification of watchdog touching.
> > When we touch the softlockup watchdog, do we also want to touch
> > the nmi watchdog?
> > 
> > Most of the time, I think we don't want to. We usually touch the
> > softlockup detector because we know we are abnormally delaying
> > the softlockup kthread from being scheduled, and if we are in such
> > situation, it means we are doing something in a sensitive context:
> > typically the kind of context favorable to create hardlockups...
> > 
> > But the opposite is right: if we touch the nmi watchdog: it means we
> > are abnormally delaying irqs, which means we also are abnormally
> > delaying the softlockup kthread from being scheduled, so if we
> > touch the nmi watchdog, we also want to touch the softlockup
> > detector.
> > 
> > Hence I guess we want to keep the current state:
> > 
> > - touch_nmi_watchdog() = touch softlockup and nmi watchdogs
> > - touch_softlockup_watchdog() = only touch softlockup watchdog
> 
> Hmm ok I see what you are saying.  A little tweak and I have this
> compiled-tested only patch that I think satisifies you.
> 
> I didn't really touch the touch_nmi_watchdog() code in the kernel, so it
> still calls a stub function in kernel/watchdog.c.  Add a boolean to that
> path and I think it accomplishes the logic you are looking for.
> 
> Cheers,
> Don


Yeah looks good.

Could you send this patch with a changelog and your sign-off?

Thanks!

> 
> 
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 9898c7c..c1a89ac 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -31,6 +31,7 @@ int watchdog_enabled;
>  int __read_mostly softlockup_thresh = 60;
>  
>  static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts);
> +static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
>  static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog);
>  static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer);
>  static DEFINE_PER_CPU(bool, watchdog_touch_sync);
> @@ -147,6 +148,7 @@ void touch_watchdog_sync(void)
>  
>  void touch_nmi_watchdog(void)
>  {
> +	__get_cpu_var(watchdog_nmi_touch) = true;
>  	touch_watchdog();
>  }
>  EXPORT_SYMBOL(touch_nmi_watchdog);
> @@ -203,11 +205,10 @@ void watchdog_overflow_callback(struct perf_event *event, int nmi,
>  		 struct pt_regs *regs)
>  {
>  	int this_cpu = smp_processor_id();
> -	unsigned long touch_ts = per_cpu(watchdog_touch_ts, this_cpu);
>  	char warn = per_cpu(watchdog_warn, this_cpu);
>  
> -	if (touch_ts == 0) {
> -		__touch_watchdog();
> +	if (__get_cpu_var(watchdog_nmi_touch) == true) {
> +		__get_cpu_var(watchdog_nmi_touch) = false;
>  		return;
>  	}
>  

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