Re: [RESEND] devfreq: governor: Save void *data in the governor userspace

From: Kant Fan
Date: Wed Sep 14 2022 - 05:26:33 EST


On 3/29/2022 5:14 PM, Kant Fan wrote:
The member void *data in the structure devfreq can be overwrite
by governor_userspace. For example:
1. The device driver assigned the devfreq governor to simple_ondemand
by the function devfreq_add_device() and init the devfreq member
void *data to a pointer of a static structure devfreq_simple_ondemand_data
by the function devfreq_add_device().
2. The user changed the devfreq governor to userspace by the command
"echo userspace > /sys/class/devfreq/.../governor".
3. The governor userspace alloced a dynamic memory for the struct
userspace_data and assigend the member void *data of devfreq to
this memory by the function userspace_init().
4. The user changed the devfreq governor back to simple_ondemand
by the command "echo simple_ondemand > /sys/class/devfreq/.../governor".
5. The governor userspace exited and assigned the member void *data
in the structure devfreq to NULL by the function userspace_exit().
6. The governor simple_ondemand fetched the static information of
devfreq_simple_ondemand_data in the function
devfreq_simple_ondemand_func() but the member void *data of devfreq was
assigned to NULL by the function userspace_exit().
7. The information of upthreshold and downdifferential is lost
and the governor simple_ondemand can't work correctly.

The member void *data in the structure devfreq is designed for
a static pointer used in a governor and inited by the function
devfreq_add_device(). So if a governor want to use void *data
to do some other things, it must save void *data in the init()
function and restore void *data in the exit() function.

Signed-off-by: Kant Fan <kant@xxxxxxxxxxxxxxxxx>
---
drivers/devfreq/governor_userspace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
index ab9db7adb3ad..dbbb448dcbcf 100644
--- a/drivers/devfreq/governor_userspace.c
+++ b/drivers/devfreq/governor_userspace.c
@@ -17,6 +17,7 @@
struct userspace_data {
unsigned long user_frequency;
bool valid;
+ void *saved_data;
};
static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
@@ -91,6 +92,7 @@ static int userspace_init(struct devfreq *devfreq)
goto out;
}
data->valid = false;
+ data->saved_data = devfreq->data;
devfreq->data = data;
err = sysfs_create_group(&devfreq->dev.kobj, &dev_attr_group);
@@ -100,6 +102,8 @@ static int userspace_init(struct devfreq *devfreq)
static void userspace_exit(struct devfreq *devfreq)
{
+ struct userspace_data *data = devfreq->data;
+ void *saved_data = data->saved_data;
/*
* Remove the sysfs entry, unless this is being called after
* device_del(), which should have done this already via kobject_del().
@@ -108,7 +112,7 @@ static void userspace_exit(struct devfreq *devfreq)
sysfs_remove_group(&devfreq->dev.kobj, &dev_attr_group);
kfree(devfreq->data);
- devfreq->data = NULL;
+ devfreq->data = saved_data;
}
static int devfreq_userspace_handler(struct devfreq *devfreq,

Dear MyungJoo, Kyungmin & Chanwoo,
Gently ping this issue... Does this patch has a chance to be accepted?
This seems to be a bug in devfreq userspace governor, which affects the switching between governors -- When switching from userspace to ondemand, the ondemand governor would be invalid.
If there's any question, please let me know.
Thank you.

--
Best Regards,
Kant Fan