evie/android_kernel_oneplus_msm8998
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cpufreq: Register for hotplug notifier before locking hotplug

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If a CPU hotplug operation occurs in parallel while a driver is
registering with the cpufreq framework it can lead to the following
deadlock scenario:
Thread A (cpufreq_register_driver())	Thread B (cpu_down())
get_online_cpus()
	|
atomic_inc(&cpu_hotplug.refcount)
					     cpu_down()
						|
				     mutex_lock(&cpu_add_remove_lock)
						|
				     cpu_hotplug_begin() waits on
				     cpu_hotplug.refcount to reset
register_cpu_notifier()
	|
mutex_lock(&cpu_add_remove_lock)

This happens because the registration for hotplug notifiers happens
inside the hotplug locked section.
This change moves hotplug registration call before get_online_cpus()
to avoid the deadlock.

Change-Id: Ia59a3e2710133d3b3608e49938e746e58af5a6d4
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>
This commit is contained in:
Rohit Gupta 2016-12-19 10:44:16 -08:00
parent a80e267a8c
commit d36dd7737c
1 changed files with 6 additions and 1 deletions
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7
drivers/cpufreq/cpufreq.c
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@ -2269,6 +2269,9 @@ static int cpufreq_cpu_callback(struct notifier_block *nfb,
{
unsigned int cpu = (unsigned long)hcpu;
if (!cpufreq_driver)
return NOTIFY_OK;
switch (action & ~CPU_TASKS_FROZEN) {
case CPU_ONLINE:
cpufreq_online(cpu);
@ -2435,6 +2438,9 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
pr_debug("trying to register driver %s\n", driver_data->name);
/* Register for hotplug notifers before blocking hotplug. */
register_hotcpu_notifier(&cpufreq_cpu_notifier);
/* Protect against concurrent CPU online/offline. */
get_online_cpus();
@ -2466,7 +2472,6 @@ int cpufreq_register_driver(struct cpufreq_driver *driver_data)
goto err_if_unreg;
}
register_hotcpu_notifier(&cpufreq_cpu_notifier);
pr_info("driver %s up and running\n", driver_data->name);
out: