clocksource: Make watchdog robust vs. interruption
The clocksource watchdog code is interruptible and it has been
observed that this can trigger false positives which disable the TSC.
The reason is that an interrupt storm or a long running interrupt
handler between the read of the watchdog source and the read of the
TSC brings the two far enough apart that the delta is larger than the
unstable treshold. Move both reads into a short interrupt disabled
region to avoid that.
Reported-and-tested-by: Vernon Mauery <vernux@us.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index d4646b4..18a1baf 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -188,6 +188,7 @@
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
/* Watchdog related data, used by the framework */
struct list_head wd_list;
+ cycle_t cs_last;
cycle_t wd_last;
#endif
} ____cacheline_aligned;
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 1c95fd6..e0980f0 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -185,7 +185,6 @@
static struct timer_list watchdog_timer;
static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
static DEFINE_SPINLOCK(watchdog_lock);
-static cycle_t watchdog_last;
static int watchdog_running;
static int clocksource_watchdog_kthread(void *data);
@@ -254,11 +253,6 @@
if (!watchdog_running)
goto out;
- wdnow = watchdog->read(watchdog);
- wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
- watchdog->mult, watchdog->shift);
- watchdog_last = wdnow;
-
list_for_each_entry(cs, &watchdog_list, wd_list) {
/* Clocksource already marked unstable? */
@@ -268,19 +262,28 @@
continue;
}
+ local_irq_disable();
csnow = cs->read(cs);
+ wdnow = watchdog->read(watchdog);
+ local_irq_enable();
/* Clocksource initialized ? */
if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
cs->flags |= CLOCK_SOURCE_WATCHDOG;
- cs->wd_last = csnow;
+ cs->wd_last = wdnow;
+ cs->cs_last = csnow;
continue;
}
- /* Check the deviation from the watchdog clocksource. */
- cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
+ wd_nsec = clocksource_cyc2ns((wdnow - cs->wd_last) & watchdog->mask,
+ watchdog->mult, watchdog->shift);
+
+ cs_nsec = clocksource_cyc2ns((csnow - cs->cs_last) &
cs->mask, cs->mult, cs->shift);
- cs->wd_last = csnow;
+ cs->cs_last = csnow;
+ cs->wd_last = wdnow;
+
+ /* Check the deviation from the watchdog clocksource. */
if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
clocksource_unstable(cs, cs_nsec - wd_nsec);
continue;
@@ -318,7 +321,6 @@
return;
init_timer(&watchdog_timer);
watchdog_timer.function = clocksource_watchdog;
- watchdog_last = watchdog->read(watchdog);
watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
watchdog_running = 1;