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authorAnton Blanchard <anton@samba.org>2014-05-09 17:47:12 +1000
committerBenjamin Herrenschmidt <benh@kernel.crashing.org>2014-05-12 14:29:28 +1000
commit8050936caf125fbe54111ba5e696b68a360556ba (patch)
treeba4bbad4f5227c55f9229a043cae6c34d7f1c379 /arch/powerpc/kernel/time.c
parent372cf1244d7c271806b83b32b09a1c8b1b31b353 (diff)
downloadblackbird-op-linux-8050936caf125fbe54111ba5e696b68a360556ba.tar.gz
blackbird-op-linux-8050936caf125fbe54111ba5e696b68a360556ba.zip
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 <anton@samba.org> Cc: stable@vger.kernel.org # 3.14+ Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Diffstat (limited to 'arch/powerpc/kernel/time.c')
-rw-r--r--arch/powerpc/kernel/time.c3
1 files changed, 0 insertions, 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);
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