linux/drivers/clocksource/dummy_timer.c
Srivatsa S. Bhat 8daa127f4e clocksource, dummy-timer: Fix CPU hotplug callback registration
Subsystems that want to register CPU hotplug callbacks, as well as perform
initialization for the CPUs that are already online, often do it as shown
below:

	get_online_cpus();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	register_cpu_notifier(&foobar_cpu_notifier);

	put_online_cpus();

This is wrong, since it is prone to ABBA deadlocks involving the
cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently
with CPU hotplug operations).

Instead, the correct and race-free way of performing the callback
registration is:

	cpu_notifier_register_begin();

	for_each_online_cpu(cpu)
		init_cpu(cpu);

	/* Note the use of the double underscored version of the API */
	__register_cpu_notifier(&foobar_cpu_notifier);

	cpu_notifier_register_done();

Fix the clocksource dummy-timer code by using this latter form of callback
registration.

Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
2014-03-20 13:43:45 +01:00

75 lines
1.8 KiB
C

/*
* linux/drivers/clocksource/dummy_timer.c
*
* Copyright (C) 2013 ARM Ltd.
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/clockchips.h>
#include <linux/cpu.h>
#include <linux/init.h>
#include <linux/percpu.h>
#include <linux/cpumask.h>
static DEFINE_PER_CPU(struct clock_event_device, dummy_timer_evt);
static void dummy_timer_set_mode(enum clock_event_mode mode,
struct clock_event_device *evt)
{
/*
* Core clockevents code will call this when exchanging timer devices.
* We don't need to do anything here.
*/
}
static void dummy_timer_setup(void)
{
int cpu = smp_processor_id();
struct clock_event_device *evt = __this_cpu_ptr(&dummy_timer_evt);
evt->name = "dummy_timer";
evt->features = CLOCK_EVT_FEAT_PERIODIC |
CLOCK_EVT_FEAT_ONESHOT |
CLOCK_EVT_FEAT_DUMMY;
evt->rating = 100;
evt->set_mode = dummy_timer_set_mode;
evt->cpumask = cpumask_of(cpu);
clockevents_register_device(evt);
}
static int dummy_timer_cpu_notify(struct notifier_block *self,
unsigned long action, void *hcpu)
{
if ((action & ~CPU_TASKS_FROZEN) == CPU_STARTING)
dummy_timer_setup();
return NOTIFY_OK;
}
static struct notifier_block dummy_timer_cpu_nb = {
.notifier_call = dummy_timer_cpu_notify,
};
static int __init dummy_timer_register(void)
{
int err = 0;
cpu_notifier_register_begin();
err = __register_cpu_notifier(&dummy_timer_cpu_nb);
if (err)
goto out;
/* We won't get a call on the boot CPU, so register immediately */
if (num_possible_cpus() > 1)
dummy_timer_setup();
out:
cpu_notifier_register_done();
return err;
}
early_initcall(dummy_timer_register);