Re: [PATCH 2/6] [watchdog] convert touch_softlockup_watchdog to touch_watchdog

Don Zickus
2010-04-21T21:32:31Z

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@redhat.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

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;
}