Hi Jiri,
On Wed, Sep 03, 2014 at 03:04:28PM +0200, Jiri Kosina wrote:
> There is a following AB-BA dependency between cpu_hotplug.lock and
> cpuidle_lock:
>
> 1) cpu_hotplug.lock -> cpuidle_lock
> enable_nonboot_cpus()
> _cpu_up()
> cpu_hotplug_being()
> LOCK(cpu_hotplug.lock)
> cpu_notify()
> ...
> acpi_processor_hotplug()
> cpuidle_pause_and_lock()
> LOCK(cpuidle_lock)
>
> 2) cpuidle_lock -> cpu_hotplug.lock
> acpi_os_execute_deferred() workqueue
> ...
> acpi_processor_cst_has_changed()
> cpuidle_pause_and_lock()
> LOCK(cpuidle_lock)
> get_online_cpus()
> LOCK(cpu_hotplug.lock)
>
> Fix this by reversing the order acpi_processor_cst_has_changed() does
> thigs -- let it first execute the protection against CPU hotplug by
> calling get_online_cpus() and obtain the cpuidle lock only after that (and
> perform the symmentric change when allowing CPUs hotplug again and
> dropping cpuidle lock).
>
> Spotted by lockdep.
>
> Signed-off-by: Jiri Kosina <jkos...@suse.cz>
Looks good to me.
Reviewed-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> ---
> drivers/acpi/processor_idle.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
> index 3dca36d..17f9ec5 100644
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -1071,9 +1071,9 @@ int acpi_processor_cst_has_changed(struct
> acpi_processor *pr)
>
> if (pr->id == 0 && cpuidle_get_driver() == &acpi_idle_driver) {
>
> - cpuidle_pause_and_lock();
> /* Protect against cpu-hotplug */
> get_online_cpus();
> + cpuidle_pause_and_lock();
>
> /* Disable all cpuidle devices */
> for_each_online_cpu(cpu) {
> @@ -1100,8 +1100,8 @@ int acpi_processor_cst_has_changed(struct
> acpi_processor *pr)
> cpuidle_enable_device(dev);
> }
> }
> - put_online_cpus();
> cpuidle_resume_and_unlock();
> + put_online_cpus();
> }
>
> return 0;
> --
> Jiri Kosina
> SUSE Labs
>
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