Commit 6726655d authored Sep 03, 2014 by Jiri Kosina Committed by Rafael J. Wysocki Sep 03, 2014

ACPI / cpuidle: fix deadlock between cpuidle_lock and cpu_hotplug.lock



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_begin()
   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 <jkosina@suse.cz>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

parent 69e273c0

drivers/acpi/processor_idle.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -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;