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Date: Tue, 7 Jul 2015 09:31:05 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Sudeep Holla <sudeep.holla@....com>
cc: LKML <linux-kernel@...r.kernel.org>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
Suzuki Poulose <Suzuki.Poulose@....com>,
Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
Catalin Marinas <Catalin.Marinas@....com>,
"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [patch 1/2] tick/broadcast: Prevent deep idle states if no
broadcast device available
On Mon, 6 Jul 2015, Thomas Gleixner wrote:
> On Mon, 6 Jul 2015, Sudeep Holla wrote:
> > This triggered the below crash on boot, looks like it's accessing
> > hrtimer->function which is null in periodic mode IIUC
> >
> > Regards,
> > Sudeep
>
> Gah. I have no idea how that gets queued. /me goes off to tweak x86 to
> emulate that crap.
So with a less heat damaged brain, I think I was able to decode the
twisted logic behind all this.
Can you test the patch below please?
Thanks,
tglx
---
Index: tip/include/linux/tick.h
===================================================================
--- tip.orig/include/linux/tick.h
+++ tip/include/linux/tick.h
@@ -67,11 +67,7 @@ extern void tick_broadcast_control(enum
static inline void tick_broadcast_control(enum tick_broadcast_mode mode) { }
#endif /* BROADCAST */
-#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT)
extern int tick_broadcast_oneshot_control(enum tick_broadcast_state state);
-#else
-static inline int tick_broadcast_oneshot_control(enum tick_broadcast_state state) { return 0; }
-#endif
static inline void tick_broadcast_enable(void)
{
Index: tip/kernel/time/tick-broadcast.c
===================================================================
--- tip.orig/kernel/time/tick-broadcast.c
+++ tip/kernel/time/tick-broadcast.c
@@ -159,7 +159,7 @@ int tick_device_uses_broadcast(struct cl
{
struct clock_event_device *bc = tick_broadcast_device.evtdev;
unsigned long flags;
- int ret;
+ int ret = 0;
raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
@@ -221,13 +221,14 @@ int tick_device_uses_broadcast(struct cl
* If we kept the cpu in the broadcast mask,
* tell the caller to leave the per cpu device
* in shutdown state. The periodic interrupt
- * is delivered by the broadcast device.
+ * is delivered by the broadcast device, if
+ * the broadcast device exists and is not
+ * hrtimer based.
*/
- ret = cpumask_test_cpu(cpu, tick_broadcast_mask);
+ if (bc && !(bc->features & CLOCK_EVT_FEAT_HRTIMER))
+ ret = cpumask_test_cpu(cpu, tick_broadcast_mask);
break;
default:
- /* Nothing to do */
- ret = 0;
break;
}
}
@@ -265,8 +266,22 @@ static bool tick_do_broadcast(struct cpu
* Check, if the current cpu is in the mask
*/
if (cpumask_test_cpu(cpu, mask)) {
+ struct clock_event_device *bc = tick_broadcast_device.evtdev;
+
cpumask_clear_cpu(cpu, mask);
- local = true;
+ /*
+ * We only run the local handler, if the broadcast
+ * device is not hrtimer based. Otherwise we run into
+ * a hrtimer recursion.
+ *
+ * local timer_interrupt()
+ * local_handler()
+ * expire_hrtimers()
+ * bc_handler()
+ * local_handler()
+ * expire_hrtimers()
+ */
+ local = !(bc->features & CLOCK_EVT_FEAT_HRTIMER);
}
if (!cpumask_empty(mask)) {
@@ -359,8 +374,16 @@ void tick_broadcast_control(enum tick_br
case TICK_BROADCAST_ON:
cpumask_set_cpu(cpu, tick_broadcast_on);
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_mask)) {
- if (tick_broadcast_device.mode ==
- TICKDEV_MODE_PERIODIC)
+ /*
+ * Only shutdown the cpu local device, if:
+ *
+ * - the broadcast device exists
+ * - the broadcast device is not a hrtimer based one
+ * - the broadcast device is in periodic mode to
+ * avoid a hickup during switch to oneshot mode
+ */
+ if (bc && !(bc->features & CLOCK_EVT_FEAT_HRTIMER) &&
+ tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
clockevents_shutdown(dev);
}
break;
@@ -662,71 +685,82 @@ static void broadcast_shutdown_local(str
clockevents_switch_state(dev, CLOCK_EVT_STATE_SHUTDOWN);
}
-/**
- * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
- * @state: The target state (enter/exit)
- *
- * The system enters/leaves a state, where affected devices might stop
- * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
- *
- * Called with interrupts disabled, so clockevents_lock is not
- * required here because the local clock event device cannot go away
- * under us.
- */
-int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
{
struct clock_event_device *bc, *dev;
- struct tick_device *td;
int cpu, ret = 0;
ktime_t now;
/*
- * Periodic mode does not care about the enter/exit of power
- * states
+ * If there is no broadcast device, tell the caller not to go
+ * into deep idle.
*/
- if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
- return 0;
+ if (!tick_broadcast_device.evtdev)
+ return -EBUSY;
- /*
- * We are called with preemtion disabled from the depth of the
- * idle code, so we can't be moved away.
- */
- td = this_cpu_ptr(&tick_cpu_device);
- dev = td->evtdev;
-
- if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
- return 0;
+ dev = this_cpu_ptr(&tick_cpu_device)->evtdev;
raw_spin_lock(&tick_broadcast_lock);
bc = tick_broadcast_device.evtdev;
cpu = smp_processor_id();
if (state == TICK_BROADCAST_ENTER) {
+ /*
+ * If the current CPU owns the hrtimer broadcast
+ * mechanism, it cannot go deep idle and we do not add
+ * the CPU to the broadcast mask. We don't have to go
+ * through the EXIT path as the local timer is not
+ * shutdown.
+ */
+ ret = broadcast_needs_cpu(bc, cpu);
+ if (ret)
+ goto out;
+
+ /*
+ * If the broadcast device is in periodic mode, we
+ * return.
+ */
+ if (tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC) {
+ /* If it is a hrtimer based broadcast, return busy */
+ if (bc->features & CLOCK_EVT_FEAT_HRTIMER)
+ ret = -EBUSY;
+ goto out;
+ }
+
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
+
+ /* Conditionally shut down the local timer. */
broadcast_shutdown_local(bc, dev);
+
/*
* We only reprogram the broadcast timer if we
* did not mark ourself in the force mask and
* if the cpu local event is earlier than the
* broadcast event. If the current CPU is in
* the force mask, then we are going to be
- * woken by the IPI right away.
+ * woken by the IPI right away; we return
+ * busy, so the CPU does not try to go deep
+ * idle.
*/
- if (!cpumask_test_cpu(cpu, tick_broadcast_force_mask) &&
- dev->next_event.tv64 < bc->next_event.tv64)
+ if (cpumask_test_cpu(cpu, tick_broadcast_force_mask)) {
+ ret = -EBUSY;
+ } else if (dev->next_event.tv64 < bc->next_event.tv64) {
tick_broadcast_set_event(bc, cpu, dev->next_event);
+ /*
+ * In case of hrtimer broadcasts the
+ * programming might have moved the
+ * timer to this cpu. If yes, remove
+ * us from the broadcast mask and
+ * return busy.
+ */
+ ret = broadcast_needs_cpu(bc, cpu);
+ if (ret) {
+ cpumask_clear_cpu(cpu,
+ tick_broadcast_oneshot_mask);
+ }
+ }
}
- /*
- * If the current CPU owns the hrtimer broadcast
- * mechanism, it cannot go deep idle and we remove the
- * CPU from the broadcast mask. We don't have to go
- * through the EXIT path as the local timer is not
- * shutdown.
- */
- ret = broadcast_needs_cpu(bc, cpu);
- if (ret)
- cpumask_clear_cpu(cpu, tick_broadcast_oneshot_mask);
} else {
if (cpumask_test_and_clear_cpu(cpu, tick_broadcast_oneshot_mask)) {
clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
@@ -938,6 +972,16 @@ bool tick_broadcast_oneshot_available(vo
return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;
}
+#else
+int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ struct clock_event_device *bc = tick_broadcast_device.evtdev;
+
+ if (!bc || (bc->features & CLOCK_EVT_FEAT_HRTIMER)
+ return -EBUSY;
+
+ return 0;
+}
#endif
void __init tick_broadcast_init(void)
Index: tip/kernel/time/tick-common.c
===================================================================
--- tip.orig/kernel/time/tick-common.c
+++ tip/kernel/time/tick-common.c
@@ -343,6 +343,27 @@ out_bc:
tick_install_broadcast_device(newdev);
}
+/**
+ * tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
+ * @state: The target state (enter/exit)
+ *
+ * The system enters/leaves a state, where affected devices might stop
+ * Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
+ *
+ * Called with interrupts disabled, so clockevents_lock is not
+ * required here because the local clock event device cannot go away
+ * under us.
+ */
+int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
+
+ if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
+ return 0;
+
+ return __tick_broadcast_oneshot_control(state);
+}
+
#ifdef CONFIG_HOTPLUG_CPU
/*
* Transfer the do_timer job away from a dying cpu.
Index: tip/kernel/time/tick-sched.h
===================================================================
--- tip.orig/kernel/time/tick-sched.h
+++ tip/kernel/time/tick-sched.h
@@ -71,4 +71,14 @@ extern void tick_cancel_sched_timer(int
static inline void tick_cancel_sched_timer(int cpu) { }
#endif
+#ifdef CONFIG_GENERIC_CLOCKEVENTS_BROADCAST
+extern int __tick_broadcast_oneshot_control(enum tick_broadcast_state state);
+#else
+static inline int
+__tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ return -EBUSY;
+}
+#endif
+
#endif
--
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