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Subject[PATCH 35/51] acpi-cpufreq: Fix CPU hotplug callback registration
Date
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_maps_update_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_maps_update_done();


Fix the acpi-cpufreq code by using this latter form of callback registration.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: cpufreq@vger.kernel.org
Cc: linux-pm@vger.kernel.org
Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
---

drivers/cpufreq/acpi-cpufreq.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 18448a7..e2eb471 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -907,15 +907,16 @@ static void __init acpi_cpufreq_boost_init(void)

acpi_cpufreq_driver.boost_supported = true;
acpi_cpufreq_driver.boost_enabled = boost_state(0);
- get_online_cpus();
+
+ cpu_maps_update_begin();

/* Force all MSRs to the same value */
boost_set_msrs(acpi_cpufreq_driver.boost_enabled,
cpu_online_mask);

- register_cpu_notifier(&boost_nb);
+ __register_cpu_notifier(&boost_nb);

- put_online_cpus();
+ cpu_maps_update_done();
}
}



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