hrtimers: allow the hot-unplugging of all cpus
Impact: fix CPU hotplug hang on Power6 testbox
On architectures that support offlining all cpus (at least powerpc/pseries),
hot-unpluging the tick_do_timer_cpu can result in a system hang.
This comes from the fact that if the cpu going down happens to be the
cpu doing the tick, then as the tick_do_timer_cpu handover happens after the
cpu is dead (via the CPU_DEAD notification), we're left without ticks,
jiffies are frozen and any task relying on timers (msleep, ...) is stuck.
That's particularly the case for the cpu looping in __cpu_die() waiting
for the dying cpu to be dead.
This patch addresses this by having the tick_do_timer_cpu handover happen
earlier during the CPU_DYING notification. For this, a new clockevent
notification type is introduced (CLOCK_EVT_NOTIFY_CPU_DYING) which is triggered
in hrtimer_cpu_notify().
Signed-off-by: Sebastien Dugue <sebastien.dugue@bull.net>
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/clockchips.h b/include/linux/clockchips.h
index cea1536..3a1dbba 100644
--- a/include/linux/clockchips.h
+++ b/include/linux/clockchips.h
@@ -36,6 +36,7 @@
CLOCK_EVT_NOTIFY_BROADCAST_EXIT,
CLOCK_EVT_NOTIFY_SUSPEND,
CLOCK_EVT_NOTIFY_RESUME,
+ CLOCK_EVT_NOTIFY_CPU_DYING,
CLOCK_EVT_NOTIFY_CPU_DEAD,
};
diff --git a/kernel/hrtimer.c b/kernel/hrtimer.c
index 8fea312..647a40e 100644
--- a/kernel/hrtimer.c
+++ b/kernel/hrtimer.c
@@ -1608,6 +1608,10 @@
break;
#ifdef CONFIG_HOTPLUG_CPU
+ case CPU_DYING:
+ case CPU_DYING_FROZEN:
+ clockevents_notify(CLOCK_EVT_NOTIFY_CPU_DYING, &scpu);
+ break;
case CPU_DEAD:
case CPU_DEAD_FROZEN:
{
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 63e05d4..21a5ca8 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -274,6 +274,21 @@
}
/*
+ * Transfer the do_timer job away from a dying cpu.
+ *
+ * Called with interrupts disabled.
+ */
+static void tick_handover_do_timer(int *cpup)
+{
+ if (*cpup == tick_do_timer_cpu) {
+ int cpu = cpumask_first(cpu_online_mask);
+
+ tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
+ TICK_DO_TIMER_NONE;
+ }
+}
+
+/*
* Shutdown an event device on a given cpu:
*
* This is called on a life CPU, when a CPU is dead. So we cannot
@@ -297,13 +312,6 @@
clockevents_exchange_device(dev, NULL);
td->evtdev = NULL;
}
- /* Transfer the do_timer job away from this cpu */
- if (*cpup == tick_do_timer_cpu) {
- int cpu = cpumask_first(cpu_online_mask);
-
- tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
- TICK_DO_TIMER_NONE;
- }
spin_unlock_irqrestore(&tick_device_lock, flags);
}
@@ -357,6 +365,10 @@
tick_broadcast_oneshot_control(reason);
break;
+ case CLOCK_EVT_NOTIFY_CPU_DYING:
+ tick_handover_do_timer(dev);
+ break;
+
case CLOCK_EVT_NOTIFY_CPU_DEAD:
tick_shutdown_broadcast_oneshot(dev);
tick_shutdown_broadcast(dev);