From 5e41d0d60a534d2a5dc9772600a58f44c8d12506 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Sun, 16 Sep 2007 15:36:43 +0200 Subject: [PATCH] clockevents: prevent stale tick update on offline cpu Taking a cpu offline removes the cpu from the online mask before the CPU_DEAD notification is done. The clock events layer does the cleanup of the dead CPU from the CPU_DEAD notifier chain. tick_do_timer_cpu is used to avoid xtime lock contention by assigning the task of jiffies xtime updates to one CPU. If a CPU is taken offline, then this assignment becomes stale. This went unnoticed because most of the time the offline CPU went dead before the online CPU reached __cpu_die(), where the CPU_DEAD state is checked. In the case that the offline CPU did not reach the DEAD state before we reach __cpu_die(), the code in there goes to sleep for 100ms. Due to the stale time update assignment, the system is stuck forever. Take the assignment away when a cpu is not longer in the cpu_online_mask. We do this in the last call to tick_nohz_stop_sched_tick() when the offline CPU is on the way to the final play_dead() idle entry. Signed-off-by: Thomas Gleixner --- kernel/time/tick-sched.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index b416995b975..8c3fef1db09 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -160,6 +160,18 @@ void tick_nohz_stop_sched_tick(void) cpu = smp_processor_id(); ts = &per_cpu(tick_cpu_sched, cpu); + /* + * If this cpu is offline and it is the one which updates + * jiffies, then give up the assignment and let it be taken by + * the cpu which runs the tick timer next. If we don't drop + * this here the jiffies might be stale and do_timer() never + * invoked. + */ + if (unlikely(!cpu_online(cpu))) { + if (cpu == tick_do_timer_cpu) + tick_do_timer_cpu = -1; + } + if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) goto end; -- 2.20.1