From 8050936caf125fbe54111ba5e696b68a360556ba Mon Sep 17 00:00:00 2001 From: Anton Blanchard Date: Fri, 9 May 2014 17:47:12 +1000 Subject: [PATCH] powerpc: irq work racing with timer interrupt can result in timer interrupt hang 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 Cc: stable@vger.kernel.org # 3.14+ Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/time.c | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 122a580f7322..7e711bdcc6da 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -813,9 +813,6 @@ 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); -- 2.30.2