| From | "Srivatsa S. Bhat" <> | Subject | [PATCH v2 37/52] acpi-cpufreq: Fix CPU hotplug callback registration | Date | Fri, 14 Feb 2014 13:27:37 +0530 |
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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 acpi-cpufreq code by using this latter form of callback registration.
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: Ingo Molnar <mingo@kernel.org> Cc: cpufreq@vger.kernel.org Cc: linux-pm@vger.kernel.org Acked-by: Viresh Kumar <viresh.kumar@linaro.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..245ae078e 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_notifier_register_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_notifier_register_done(); } }
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