Re: [patch 3/3] clockevents: Fix resume logic - updated version

Thomas Gleixner
2007-05-12T18:46:34Z

On Sat, 2007-05-12 at 19:01 +0200, Thomas Gleixner wrote:
> On Sat, 2007-05-12 at 09:51 -0700, Andrew Morton wrote:
> > The locking in clocksource_resume_watchdog looks pretty pointless anyway.
> > Can't we just delete it?
> >
> > The only thing it can race against is, conceivably,
> >
> > resumed = watchdog_resumed;
> > if (unlikely(resumed))
> > watchdog_resumed = 0;
> >
> > which could be solved by using test_and_clear_bit().
>
> True. I'll redo it.

Here you go.

tglx

------------------------------->
Subject: clocksource fix lock order in the resume path

lockdep complains about the lock nesting of clocksource and watchdog
lock in the resume path.

Change the resume marker to a bit operation and remove the lock from
this path.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -74,7 +74,7 @@ static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
-static int watchdog_resumed;
+static unsigned long watchdog_resumed;

/*
* Interval: 0.5sec Threshold: 0.0625s
@@ -104,9 +104,7 @@ static void clocksource_watchdog(unsigned long data)

spin_lock(&watchdog_lock);

- resumed = watchdog_resumed;
- if (unlikely(resumed))
- watchdog_resumed = 0;
+ resumed = test_and_clear_bit(0, &watchdog_resumed);

wdnow = watchdog->read();
wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
@@ -151,9 +149,7 @@ static void clocksource_watchdog(unsigned long data)
}
static void clocksource_resume_watchdog(void)
{
- spin_lock(&watchdog_lock);
- watchdog_resumed = 1;
- spin_unlock(&watchdog_lock);
+ set_bit(0, &watchdog_resumed);
}

static void clocksource_check_watchdog(struct clocksource *cs)