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: fixes-v3.17-rc4~9^2~2^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6726655dfdd2dc60c035c690d9f10cb69d7ea075;p=pandora-kernel.git

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>
---

Reading git-diff-tree failed