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@xxxxxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: cpufreq@xxxxxxxxxxxxxxx Cc: linux-pm@xxxxxxxxxxxxxxx Acked-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx> Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx> --- 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(); } } -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
