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    Subject[PATCH 3.4 07/91] ACPI / cpuidle: fix deadlock between cpuidle_lock and cpu_hotplug.lock
    Date
    From: Jiri Kosina <jkosina@suse.cz>

    3.4.105-rc1 review patch. If anyone has any objections, please let me know.

    ------------------


    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: Zefan Li <lizefan@huawei.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 6cba428..e1180ce 100644
    --- a/drivers/acpi/processor_idle.c
    +++ b/drivers/acpi/processor_idle.c
    @@ -1195,9 +1195,9 @@ 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) {
    @@ -1222,8 +1222,8 @@ 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;
    --
    1.9.1


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