[PATCH v2] cpuidle: not unset the driver if it already exist

[Zhenzhong Duan <zhenzhong.duan@oracle.com>]

__cpuidle_set_driver() check if there is an already exist driver and
unset it before return with -EBUSY. The next call will succeed as it's
just unset.

check if any of the CPUs in the mask have a driver different from drv
already and if so return -EBUSY before updating any cpuidle_drivers
per-CPU pointers.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
v2: update code logic per Rafael

 drivers/cpuidle/driver.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 80c1a83..acfce04 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -62,24 +62,23 @@ static inline void __cpuidle_unset_driver(struct cpuidle_driver *drv)
  * __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;
 }
-- 
1.8.3.1