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Date: Fri, 26 Jun 2015 09:47:34 +0200 (CEST)
From: Thomas Gleixner <tglx@...utronix.de>
To: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
cc: Sudeep Holla <sudeep.holla@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
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] clockevents: return error from tick_broadcast_oneshot_control
if !GENERIC_CLOCKEVENTS_BROADCAST
On Fri, 26 Jun 2015, Preeti U Murthy wrote:
> What about the case where GENERIC_CLOCKEVENTS_BROADCAST=y and
> TICK_ONESHOT=n (HZ_PERIODIC=y) ? Have you tested this ?
>
> This will hang the kernel at boot if you are using the hrtimer mode of
> broadcast. This is because the local timers of all cpus are shutdown
> when the cpuidle driver registers itself, on finding out that there are
> idle states where local tick devices stop. The broadcast tick device is
> then in charge of waking up the cpus at every period. In hrtimer mode of
> broadcast, there is no such real device and we hang.
Hmm, no. tick-broadcast-hrtimer.o depends on TICK_ONESHOT=y. So this
is covered by the check for the broadcast device, which is NULL.
But there is another variant:
GENERIC_CLOCKEVENTS_BROADCAST=y TICK_ONESHOT=y and 'highres=off
nohz=off' on the kernel command line.
So we need to have the broadcast_needs_cpu() check in that case as
well. Updated patch below.
Thanks,
tglx
---
diff --git a/include/linux/tick.h b/include/linux/tick.h
index 4191b5623a28..8731a58dd747 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -63,11 +63,7 @@ extern void tick_broadcast_control(enum tick_broadcast_mode mode);
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)
{
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index d39f32cdd1b5..281ce29d295e 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -662,46 +662,39 @@ static void broadcast_shutdown_local(struct clock_event_device *bc,
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 (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 the hrtimer broadcast check tells us that the
+ * cpu cannot go deep idle, or if the broadcast device
+ * is in periodic mode, we just return.
+ */
+ if (ret || tick_broadcast_device.mode == TICKDEV_MODE_PERIODIC)
+ goto out;
+
if (!cpumask_test_and_set_cpu(cpu, tick_broadcast_oneshot_mask)) {
WARN_ON_ONCE(cpumask_test_cpu(cpu, tick_broadcast_pending_mask));
broadcast_shutdown_local(bc, dev);
@@ -717,16 +710,6 @@ int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
dev->next_event.tv64 < bc->next_event.tv64)
tick_broadcast_set_event(bc, cpu, dev->next_event);
}
- /*
- * 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 +921,13 @@ bool tick_broadcast_oneshot_available(void)
return bc ? bc->features & CLOCK_EVT_FEAT_ONESHOT : false;
}
+#else
+int __tick_broadcast_oneshot_control(enum tick_broadcast_state state)
+{
+ if (!tick_broadcast_device.evtdev)
+ return -EBUSY;
+ return 0;
+}
#endif
void __init tick_broadcast_init(void)
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 17f144450050..f66c11a30348 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -342,6 +342,27 @@ 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.
diff --git a/kernel/time/tick-sched.h b/kernel/time/tick-sched.h
index 42fdf4958bcc..a4a8d4e9baa1 100644
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -71,4 +71,14 @@ extern void tick_cancel_sched_timer(int cpu);
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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