2019-10-14 00:47:19

by Zhenzhong Duan

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

__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. This is strange as we should either keep old driver and
return -EBUSY or unset and set new driver and return 0.

Signed-off-by: Zhenzhong Duan <[email protected]>
---
drivers/cpuidle/driver.c | 1 -
1 file changed, 1 deletion(-)

diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
index 80c1a83..a200304 100644
--- a/drivers/cpuidle/driver.c
+++ b/drivers/cpuidle/driver.c
@@ -74,7 +74,6 @@ static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
for_each_cpu(cpu, drv->cpumask) {

if (__cpuidle_get_cpu_driver(cpu)) {
- __cpuidle_unset_driver(drv);
return -EBUSY;
}

--
1.8.3.1

2019-10-22 17:19:27

by Rafael J. Wysocki

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

On Mon, Oct 14, 2019 at 2:43 AM Zhenzhong Duan
<[email protected]> wrote:
>
> __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. This is strange as we should either keep old driver and
> return -EBUSY or unset and set new driver and return 0.
>
> Signed-off-by: Zhenzhong Duan <[email protected]>
> ---
> drivers/cpuidle/driver.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/drivers/cpuidle/driver.c b/drivers/cpuidle/driver.c
> index 80c1a83..a200304 100644
> --- a/drivers/cpuidle/driver.c
> +++ b/drivers/cpuidle/driver.c
> @@ -74,7 +74,6 @@ static inline int __cpuidle_set_driver(struct cpuidle_driver *drv)
> for_each_cpu(cpu, drv->cpumask) {
>
> if (__cpuidle_get_cpu_driver(cpu)) {
> - __cpuidle_unset_driver(drv);
> return -EBUSY;
> }

There is a bug here, but it needs to be fixed differently.

The function should check if any of the CPUs in the mask have a driver
(which is different from drv) already and if so return -EBUSY before
updating any cpuidle_drivers per-CPU pointers.