From: Jiri Kosina <jkosina@suse.cz>
Date: Wed, 3 Sep 2014 13:04:28 +0000 (+0200)
Subject: ACPI / cpuidle: fix deadlock between cpuidle_lock and cpu_hotplug.lock
X-Git-Tag: v3.2.64~82
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5df1eb90953a86127ca130d90724819383f896da;p=thirdparty%2Fkernel%2Fstable.git

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

commit 6726655dfdd2dc60c035c690d9f10cb69d7ea075 upstream.

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>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index de0791c1025fd..388ba10055349 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1165,9 +1165,9 @@ int acpi_processor_cst_has_changed(struct acpi_processor *pr)
 	if (smp_processor_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) {
@@ -1192,8 +1192,8 @@ int acpi_processor_cst_has_changed(struct acpi_processor *pr)
 				cpuidle_enable_device(&_pr->power.dev);
 			}
 		}
-		put_online_cpus();
 		cpuidle_resume_and_unlock();
+		put_online_cpus();
 	}
 
 	return 0;