Re: [RFC PATCH v3 24/28] mm/damon/sysfs: add filters/<F>/path file

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Missing string trimming in `path_store()` causes double newlines in `path_show()` output.
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commit 355d50ee619dc1c941ec5aef02eb71147957c977
Author: SeongJae Park <sj@kernel.org>

mm/damon/sysfs: add filters/<F>/path file

Introduce a new DAMON sysfs file for letting users setup the target
memory cgroup of the belonging memory cgroup attribute monitoring.

> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index f1b7d79386866..2df1d670ee77d 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c

[ ... ]

> @@ -862,11 +867,46 @@ static ssize_t allow_store(struct kobject *kobj,
>  	return count;
>  }
>  
> +static ssize_t path_show(struct kobject *kobj,
> +		struct kobj_attribute *attr, char *buf)
> +{
> +	struct damon_sysfs_filter *filter = container_of(kobj,
> +			struct damon_sysfs_filter, kobj);
> +	int len;
> +
> +	if (!mutex_trylock(&damon_sysfs_lock))
> +		return -EBUSY;
> +	len = sysfs_emit(buf, "%s\n", filter->path ? filter->path : "");
> +	mutex_unlock(&damon_sysfs_lock);
> +	return len;
> +}
> +
> +static ssize_t path_store(struct kobject *kobj,
> +		struct kobj_attribute *attr, const char *buf, size_t count)
> +{
> +	struct damon_sysfs_filter *filter = container_of(kobj,
> +			struct damon_sysfs_filter, kobj);
> +	char *path = kmalloc_objs(*path, size_add(count, 1));
> +
> +	if (!path)
> +		return -ENOMEM;
> +	strscpy(path, buf, size_add(count, 1));

Will this strscpy() result in a double newline in the output of path_show()?

When users write to the path sysfs file using standard tools like echo, the
input typically includes a trailing newline character. This copy operation
will store that newline directly into filter->path.

When read back, path_show() uses sysfs_emit() with "%s\n", which will append
a second newline.

While a subsequent commit ("mm/damon/sysfs: setup damon_filter->memcg_id
from path") uses sysfs_streq() which safely ignores trailing newlines for
path matching, could we strip the trailing newline here to avoid the
formatting anomaly in the sysfs output?

> +	if (!mutex_trylock(&damon_sysfs_lock)) {
> +		kfree(path);
> +		return -EBUSY;
> +	}
> +	kfree(filter->path);
> +	filter->path = path;
> +	mutex_unlock(&damon_sysfs_lock);
> +	return count;
> +}

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Sashiko AI review · https://sashiko.dev/#/patchset/20260516183712.81393-1-sj@kernel.org?part=24