I am seeing an issue where a CPU running perf eventually hangs.
Traces show timer interrupts happening every 4 seconds even
when a userspace task is running on the CPU. /proc/timer_list
also shows pending hrtimers have not run in over an hour,
including the scheduler.
Looking closer, decrementers_next_tb is getting set to
0xffffffffffffffff, and at that point we will never take
a timer interrupt again.
In __timer_interrupt() we set decrementers_next_tb to
0xffffffffffffffff and rely on ->event_handler to update it:
*next_tb = ~(u64)0;
if (evt->event_handler)
evt->event_handler(evt);
In this case ->event_handler is hrtimer_interrupt. This will eventually
call back through the clockevents code with the next event to be
programmed:
static int decrementer_set_next_event(unsigned long evt,
struct clock_event_device *dev)
{
/* Don't adjust the decrementer if some irq work is pending */
if (test_irq_work_pending())
return 0;
__get_cpu_var(decrementers_next_tb) = get_tb_or_rtc() + evt;
If irq work came in between these two points, we will return
before updating decrementers_next_tb and we never process a timer
interrupt again.
This looks to have been introduced by 0215f7d8c53f (powerpc: Fix races
with irq_work). Fix it by removing the early exit and relying on
code later on in the function to force an early decrementer:
/* We may have raced with new irq work */
if (test_irq_work_pending())
set_dec(1);
Signed-off-by: Anton Blanchard <an...@samba.org>
Cc: sta...@vger.kernel.org # 3.14+
---
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 122a580..4f0b676 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -813,9 +888,6 @@ static void __init clocksource_init(void)
static int decrementer_set_next_event(unsigned long evt,
struct clock_event_device *dev)
{
- /* Don't adjust the decrementer if some irq work is pending */
- if (test_irq_work_pending())
- return 0;
__get_cpu_var(decrementers_next_tb) = get_tb_or_rtc() + evt;
set_dec(evt);
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