NOHZ: restart tick device from irq_enter()
We did not restart the tick device from irq_enter() to avoid double
reprogramming and extra events in the return immediate to idle case.
But long lasting softirqs can lead to a situation where jiffies become
stale:
idle()
tick stopped (reprogrammed to next pending timer)
halt()
interrupt
jiffies updated from irq_enter()
interrupt handler
softirq function 1 runs 20ms
softirq function 2 arms a 10ms timer with a stale jiffies value
jiffies updated from irq_exit()
timer wheel has now an already expired timer
(the one added in function 2)
timer fires and timer softirq runs
This was discovered when debugging a timer problem which happend only
when the ath5k driver is active. The debugging proved that there is a
softirq function running for more than 20ms, which is a bug by itself.
To solve this we restart the tick timer right from irq_enter(), but do
not go through the other functions which are necessary to return from
idle when need_resched() is set.
Reported-by: Elias Oltmanns <eo@nebensachen.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Elias Oltmanns <eo@nebensachen.de>
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 4692487..b1c05bf 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -36,6 +36,7 @@
extern void tick_shutdown_broadcast_oneshot(unsigned int *cpup);
extern int tick_resume_broadcast_oneshot(struct clock_event_device *bc);
extern int tick_broadcast_oneshot_active(void);
+extern void tick_check_oneshot_broadcast(int cpu);
# else /* BROADCAST */
static inline void tick_broadcast_setup_oneshot(struct clock_event_device *bc)
{
@@ -45,6 +46,7 @@
static inline void tick_broadcast_switch_to_oneshot(void) { }
static inline void tick_shutdown_broadcast_oneshot(unsigned int *cpup) { }
static inline int tick_broadcast_oneshot_active(void) { return 0; }
+static inline void tick_check_oneshot_broadcast(int cpu) { }
# endif /* !BROADCAST */
#else /* !ONESHOT */