linux-kernel - [PATCH] ACPI / cpuidle: fix deadlock between cpuidle_lock and cpu

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Date:	Wed, 3 Sep 2014 15:04:28 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	"Gautham R. Shenoy" <ego@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Srivatsa S. Bhat" <srivatsa@....edu>,
	Ingo Molnar <mingo@...nel.org>
cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org
Subject: [PATCH] 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_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 <jkosina@...e.cz>
---
 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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