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Message-ID: <1f89f5f1-8743-4902-b103-66287a33c5ba@hisilicon.com>
Date: Thu, 4 Dec 2025 15:36:47 +0800
From: Jie Zhan <zhanjie9@...ilicon.com>
To: Pengjie Zhang <zhangpengjie2@...wei.com>, <myungjoo.ham@...sung.com>,
<kyungmin.park@...sung.com>, <cw00.choi@...sung.com>
CC: <linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<zhenglifeng1@...wei.com>, <lihuisong@...wei.com>, <yubowen8@...wei.com>,
<linhongye@...artners.com>, <linuxarm@...wei.com>,
<jonathan.cameron@...wei.com>
Subject: Re: [PATCH v3] PM / devfreq: use _visible attribute to replace
create/remove_sysfs_files()
On 11/7/2025 11:17 AM, Pengjie Zhang wrote:
> Previously, non-generic attributes (polling_interval, timer) used separate
> create/delete logic, leading to race conditions during concurrent access in
> creation/deletion. Multi-threaded operations also caused inconsistencies
> between governor capabilities and attribute states.
>
> 1.Use is_visible + sysfs_update_group() to unify management of these
> attributes, eliminating creation/deletion races.
> 2.Add locks and validation to these attributes, ensuring consistency
> between current governor capabilities and attribute operations in
> multi-threaded environments.
>
> Signed-off-by: Pengjie Zhang <zhangpengjie2@...wei.com>
Hi Pengjie,
The motivation looks fine but the implementation of gov_group_visible() and
gov_attr_visible() doesn't work right in my view.
See comments below.
Thanks!
Jie
> ---
> changes in v3:
> - Use guard() to simplify lock acquisition and destruction.
> - Eliminate redundant checks for df.
> Link to v2:https://lore.kernel.org/lkml/20251028022458.2824872-1-zhangpengjie2@huawei.com/
>
> Changes in v2:
> - Fix one problem reported by the kernel test robot.
> - Redirect all error paths in timer_store() to out to ensure locks are not
> left unReleased.
> Link to v1:https://lore.kernel.org/lkml/20251025135238.3576861-1-zhangpengjie2@huawei.com/
>
> drivers/devfreq/devfreq.c | 108 ++++++++++++++++++++++++--------------
> 1 file changed, 68 insertions(+), 40 deletions(-)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 2e8d01d47f69..674b794d553d 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -38,6 +38,7 @@
>
> static struct class *devfreq_class;
> static struct dentry *devfreq_debugfs;
> +static const struct attribute_group gov_attr_group;
>
> /*
> * devfreq core provides delayed work based load monitoring helper
> @@ -785,11 +786,6 @@ static void devfreq_dev_release(struct device *dev)
> kfree(devfreq);
> }
>
> -static void create_sysfs_files(struct devfreq *devfreq,
> - const struct devfreq_governor *gov);
> -static void remove_sysfs_files(struct devfreq *devfreq,
> - const struct devfreq_governor *gov);
> -
> /**
> * devfreq_add_device() - Add devfreq feature to the device
> * @dev: the device to add devfreq feature.
> @@ -956,7 +952,10 @@ struct devfreq *devfreq_add_device(struct device *dev,
> __func__);
> goto err_init;
> }
> - create_sysfs_files(devfreq, devfreq->governor);
> +
> + err = sysfs_update_group(&devfreq->dev.kobj, &gov_attr_group);
> + if (err)
> + goto err_init;
>
> list_add(&devfreq->node, &devfreq_list);
>
> @@ -998,9 +997,7 @@ int devfreq_remove_device(struct devfreq *devfreq)
> if (devfreq->governor) {
> devfreq->governor->event_handler(devfreq,
> DEVFREQ_GOV_STOP, NULL);
> - remove_sysfs_files(devfreq, devfreq->governor);
> }
> -
> device_unregister(&devfreq->dev);
>
> return 0;
> @@ -1460,7 +1457,6 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
> __func__, df->governor->name, ret);
> goto out;
> }
> - remove_sysfs_files(df, df->governor);
>
> /*
> * Start the new governor and create the specific sysfs files
> @@ -1489,7 +1485,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
> * Create the sysfs files for the new governor. But if failed to start
> * the new governor, restore the sysfs files of previous governor.
> */
> - create_sysfs_files(df, df->governor);
> + ret = sysfs_update_group(&df->dev.kobj, &gov_attr_group);
>
> out:
> mutex_unlock(&devfreq_list_lock);
> @@ -1807,17 +1803,22 @@ static struct attribute *devfreq_attrs[] = {
> &dev_attr_trans_stat.attr,
> NULL,
> };
> -ATTRIBUTE_GROUPS(devfreq);
>
> static ssize_t polling_interval_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> struct devfreq *df = to_devfreq(dev);
> + int ret;
No need of this if restore the last line.
>
> - if (!df->profile)
> + guard(mutex)(&devfreq_list_lock);
> +
> + if (!df->profile || !df->governor ||
> + !IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
> return -EINVAL;
>
> - return sprintf(buf, "%d\n", df->profile->polling_ms);
It's fine to keep this line.
> + ret = sprintf(buf, "%d\n", df->profile->polling_ms);
> +
> + return ret;
> }
>
> static ssize_t polling_interval_store(struct device *dev,
> @@ -1828,7 +1829,10 @@ static ssize_t polling_interval_store(struct device *dev,
> unsigned int value;
> int ret;
>
> - if (!df->governor)
> + guard(mutex)(&devfreq_list_lock);
> +
> + if (!df->governor ||
> + !IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
> return -EINVAL;
>
> ret = sscanf(buf, "%u", &value);
> @@ -1847,7 +1851,10 @@ static ssize_t timer_show(struct device *dev,
> {
> struct devfreq *df = to_devfreq(dev);
>
> - if (!df->profile)
> + guard(mutex)(&devfreq_list_lock);
> +
> + if (!df->profile || !df->governor ||
> + !IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
> return -EINVAL;
>
> return sprintf(buf, "%s\n", timer_name[df->profile->timer]);
> @@ -1861,7 +1868,10 @@ static ssize_t timer_store(struct device *dev, struct device_attribute *attr,
> int timer = -1;
> int ret = 0, i;
>
> - if (!df->governor || !df->profile)
> + guard(mutex)(&devfreq_list_lock);
> +
> + if (!df->governor || !df->profile ||
> + !IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
> return -EINVAL;
>
> ret = sscanf(buf, "%16s", str_timer);
> @@ -1905,36 +1915,54 @@ static ssize_t timer_store(struct device *dev, struct device_attribute *attr,
> }
> static DEVICE_ATTR_RW(timer);
>
> -#define CREATE_SYSFS_FILE(df, name) \
> -{ \
> - int ret; \
> - ret = sysfs_create_file(&df->dev.kobj, &dev_attr_##name.attr); \
> - if (ret < 0) { \
> - dev_warn(&df->dev, \
> - "Unable to create attr(%s)\n", "##name"); \
> - } \
> -} \
> +static struct attribute *governor_attrs[] = {
> + &dev_attr_polling_interval.attr,
> + &dev_attr_timer.attr,
> + NULL
> +};
>
> -/* Create the specific sysfs files which depend on each governor. */
> -static void create_sysfs_files(struct devfreq *devfreq,
> - const struct devfreq_governor *gov)
> +static umode_t gov_attr_visible(struct kobject *kobj,
> + struct attribute *attr, int n)
> {
> - if (IS_SUPPORTED_ATTR(gov->attrs, POLLING_INTERVAL))
> - CREATE_SYSFS_FILE(devfreq, polling_interval);
> - if (IS_SUPPORTED_ATTR(gov->attrs, TIMER))
> - CREATE_SYSFS_FILE(devfreq, timer);
> + struct device *dev = kobj_to_dev(kobj);
> + struct devfreq *df = to_devfreq(dev);
> +
> + if (!df->governor || !df->governor->attrs)
> + return 0;
> +
> + if (IS_SUPPORTED_ATTR(df->governor->attrs, POLLING_INTERVAL))
> + return attr->mode;
> + if (IS_SUPPORTED_ATTR(df->governor->attrs, TIMER))
> + return attr->mode;
This would expose both 'timer' and 'polling_interval' if either of them is
supported, which is wrong.
> +
> + return 0;
> }
>
> -/* Remove the specific sysfs files which depend on each governor. */
> -static void remove_sysfs_files(struct devfreq *devfreq,
> - const struct devfreq_governor *gov)
> +static bool gov_group_visible(struct kobject *kobj)
> {
> - if (IS_SUPPORTED_ATTR(gov->attrs, POLLING_INTERVAL))
> - sysfs_remove_file(&devfreq->dev.kobj,
> - &dev_attr_polling_interval.attr);
> - if (IS_SUPPORTED_ATTR(gov->attrs, TIMER))
> - sysfs_remove_file(&devfreq->dev.kobj, &dev_attr_timer.attr);
> + struct device *dev = kobj_to_dev(kobj);
> +
> + if (!dev)
> + return false;
kobj_to_dev(kobj) can't fail. This check is unnecessary.
> +
> + return true;
> }
> +DEFINE_SYSFS_GROUP_VISIBLE(gov);
The implementation of gov_group_visible() and gov_attr_visible() doesn't
seem to comply with the design of DEFINE_SYSFS_GROUP_VISIBLE().
DEFINE_SYSFS_GROUP_VISIBLE is defined as:
#define DEFINE_SYSFS_GROUP_VISIBLE(name) \
static inline umode_t sysfs_group_visible_##name( \
struct kobject *kobj, struct attribute *attr, int n) \
{ \
if (n == 0 && !name##_group_visible(kobj)) \
return SYSFS_GROUP_INVISIBLE; \
return name##_attr_visible(kobj, attr, n); \
}
That means:
_group_visible controls whether to hide all the attrs in this group;
_attr_visible further decides whether to show each attr.
Hence,
1. gov_group_visible() should check if any attr in 'governor_attrs' should
be present, i.e. checking df->governor->attrs.
2. gov_attr_visible identifies which attr it is and checks whether the
governor supports it.
Neither is done in the above code, so this should be updated.
> +
> +static const struct attribute_group devfreq_group = {
> + .attrs = devfreq_attrs,
> +};
> +
> +static const struct attribute_group gov_attr_group = {
> + .attrs = governor_attrs,
> + .is_visible = SYSFS_GROUP_VISIBLE(gov),
> +};
> +
> +static const struct attribute_group *devfreq_groups[] = {
> + &devfreq_group,
> + &gov_attr_group,
> + NULL
> +};
>
> /**
> * devfreq_summary_show() - Show the summary of the devfreq devices
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