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authorThomas Gleixner <tglx@linutronix.de>2008-09-22 12:46:37 -0400
committerThomas Gleixner <tglx@linutronix.de>2008-09-23 05:38:52 -0400
commit6441402b1f173fa38e561d3cee7c01c32e5281ad (patch)
treefd7c81337354f39e44581530d499bcdda06d76c4 /kernel/time
parent72d31053f62c4bc464c2783974926969614a8649 (diff)
clockevents: prevent cpu online to interfere with nohz
Impact: rare hang which can be triggered on CPU online. tick_do_timer_cpu keeps track of the CPU which updates jiffies via do_timer. The value -1 is used to signal, that currently no CPU is doing this. There are two cases, where the variable can have this state: boot: necessary for systems where the boot cpu id can be != 0 nohz long idle sleep: When the CPU which did the jiffies update last goes into a long idle sleep it drops the update jiffies duty so another CPU which is not idle can pick it up and keep jiffies going. Using the same value for both situations is wrong, as the CPU online code can see the -1 state when the timer of the newly onlined CPU is setup. The setup for a newly onlined CPU goes through periodic mode and can pick up the do_timer duty without being aware of the nohz / highres mode of the already running system. Use two separate states and make them constants to avoid magic numbers confusion. Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/time')
-rw-r--r--kernel/time/tick-common.c7
-rw-r--r--kernel/time/tick-internal.h4
-rw-r--r--kernel/time/tick-sched.c8
3 files changed, 12 insertions, 7 deletions
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 019315ebf9de..b523d095decf 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -33,7 +33,7 @@ DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
33 */ 33 */
34ktime_t tick_next_period; 34ktime_t tick_next_period;
35ktime_t tick_period; 35ktime_t tick_period;
36int tick_do_timer_cpu __read_mostly = -1; 36int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
37DEFINE_SPINLOCK(tick_device_lock); 37DEFINE_SPINLOCK(tick_device_lock);
38 38
39/* 39/*
@@ -148,7 +148,7 @@ static void tick_setup_device(struct tick_device *td,
148 * If no cpu took the do_timer update, assign it to 148 * If no cpu took the do_timer update, assign it to
149 * this cpu: 149 * this cpu:
150 */ 150 */
151 if (tick_do_timer_cpu == -1) { 151 if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
152 tick_do_timer_cpu = cpu; 152 tick_do_timer_cpu = cpu;
153 tick_next_period = ktime_get(); 153 tick_next_period = ktime_get();
154 tick_period = ktime_set(0, NSEC_PER_SEC / HZ); 154 tick_period = ktime_set(0, NSEC_PER_SEC / HZ);
@@ -300,7 +300,8 @@ static void tick_shutdown(unsigned int *cpup)
300 if (*cpup == tick_do_timer_cpu) { 300 if (*cpup == tick_do_timer_cpu) {
301 int cpu = first_cpu(cpu_online_map); 301 int cpu = first_cpu(cpu_online_map);
302 302
303 tick_do_timer_cpu = (cpu != NR_CPUS) ? cpu : -1; 303 tick_do_timer_cpu = (cpu != NR_CPUS) ? cpu :
304 TICK_DO_TIMER_NONE;
304 } 305 }
305 spin_unlock_irqrestore(&tick_device_lock, flags); 306 spin_unlock_irqrestore(&tick_device_lock, flags);
306} 307}
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 6e9db9734aa6..e18014fadf95 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -1,6 +1,10 @@
1/* 1/*
2 * tick internal variable and functions used by low/high res code 2 * tick internal variable and functions used by low/high res code
3 */ 3 */
4
5#define TICK_DO_TIMER_NONE -1
6#define TICK_DO_TIMER_BOOT -2
7
4DECLARE_PER_CPU(struct tick_device, tick_cpu_device); 8DECLARE_PER_CPU(struct tick_device, tick_cpu_device);
5extern spinlock_t tick_device_lock; 9extern spinlock_t tick_device_lock;
6extern ktime_t tick_next_period; 10extern ktime_t tick_next_period;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index a87b0468568b..31a14e8caac1 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -221,7 +221,7 @@ void tick_nohz_stop_sched_tick(int inidle)
221 */ 221 */
222 if (unlikely(!cpu_online(cpu))) { 222 if (unlikely(!cpu_online(cpu))) {
223 if (cpu == tick_do_timer_cpu) 223 if (cpu == tick_do_timer_cpu)
224 tick_do_timer_cpu = -1; 224 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
225 } 225 }
226 226
227 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE)) 227 if (unlikely(ts->nohz_mode == NOHZ_MODE_INACTIVE))
@@ -303,7 +303,7 @@ void tick_nohz_stop_sched_tick(int inidle)
303 * invoked. 303 * invoked.
304 */ 304 */
305 if (cpu == tick_do_timer_cpu) 305 if (cpu == tick_do_timer_cpu)
306 tick_do_timer_cpu = -1; 306 tick_do_timer_cpu = TICK_DO_TIMER_NONE;
307 307
308 ts->idle_sleeps++; 308 ts->idle_sleeps++;
309 309
@@ -468,7 +468,7 @@ static void tick_nohz_handler(struct clock_event_device *dev)
468 * this duty, then the jiffies update is still serialized by 468 * this duty, then the jiffies update is still serialized by
469 * xtime_lock. 469 * xtime_lock.
470 */ 470 */
471 if (unlikely(tick_do_timer_cpu == -1)) 471 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
472 tick_do_timer_cpu = cpu; 472 tick_do_timer_cpu = cpu;
473 473
474 /* Check, if the jiffies need an update */ 474 /* Check, if the jiffies need an update */
@@ -570,7 +570,7 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
570 * this duty, then the jiffies update is still serialized by 570 * this duty, then the jiffies update is still serialized by
571 * xtime_lock. 571 * xtime_lock.
572 */ 572 */
573 if (unlikely(tick_do_timer_cpu == -1)) 573 if (unlikely(tick_do_timer_cpu == TICK_DO_TIMER_NONE))
574 tick_do_timer_cpu = cpu; 574 tick_do_timer_cpu = cpu;
575#endif 575#endif
576 576