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    Subject[PATCH 3.16 035/148] cpuidle: Do not unset the driver if it is there already
    3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Zhenzhong Duan <zhenzhong.duan@oracle.com>

    commit 918c1fe9fbbe46fcf56837ff21f0ef96424e8b29 upstream.

    Fix __cpuidle_set_driver() to check if any of the CPUs in the mask has
    a driver different from drv already and, if so, return -EBUSY before
    updating any cpuidle_drivers per-CPU pointers.

    Fixes: 82467a5a885d ("cpuidle: simplify multiple driver support")
    Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
    [ rjw: Subject & changelog ]
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/cpuidle/driver.c | 15 +++++++--------
    1 file changed, 7 insertions(+), 8 deletions(-)

    --- a/drivers/cpuidle/driver.c
    +++ b/drivers/cpuidle/driver.c
    @@ -60,24 +60,23 @@ static inline void __cpuidle_unset_drive
    * __cpuidle_set_driver - set per CPU driver variables for the given driver.
    * @drv: a valid pointer to a struct cpuidle_driver
    *
    - * For each CPU in the driver's cpumask, unset the registered driver per CPU
    - * to @drv.
    - *
    - * Returns 0 on success, -EBUSY if the CPUs have driver(s) already.
    + * Returns 0 on success, -EBUSY if any CPU in the cpumask have a driver
    + * different from drv already.
    */
    static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
    {
    int cpu;

    for_each_cpu(cpu, drv->cpumask) {
    + struct cpuidle_driver *old_drv;

    - if (__cpuidle_get_cpu_driver(cpu)) {
    - __cpuidle_unset_driver(drv);
    + old_drv = __cpuidle_get_cpu_driver(cpu);
    + if (old_drv && old_drv != drv)
    return -EBUSY;
    - }
    + }

    + for_each_cpu(cpu, drv->cpumask)
    per_cpu(cpuidle_drivers, cpu) = drv;
    - }

    return 0;
    }
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