Re: [RFC PATCH 6/9] mm/damon/sysfs-schemes: kobject_del() scheme quota goal dirs

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Missing Kobject Deletion on Error Path
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commit b01a934762aa810a11a4a01efdd70c41f7274410
Author: SeongJae Park <sj@kernel.org>

mm/damon/sysfs-schemes: kobject_del() scheme quota goal dirs

This commit adds missing kobject_del() calls to the cleanup of scheme quota
goal directories. This prevents directory creation failures due to name
conflicts when CONFIG_DEBUG_KOBJECT_RELEASE is enabled.

> diff --git a/mm/damon/sysfs-schemes.c b/mm/damon/sysfs-schemes.c
> index 300930c2c5b3f..737638be84f15 100644
> --- a/mm/damon/sysfs-schemes.c
> +++ b/mm/damon/sysfs-schemes.c
> @@ -1465,8 +1465,10 @@ static void damos_sysfs_quota_goals_rm_dirs(
>  	struct damos_sysfs_quota_goal **goals_arr = goals->goals_arr;
>  	int i;
>  
> -	for (i = 0; i < goals->nr; i++)
> +	for (i = 0; i < goals->nr; i++) {
> +		kobject_del(&goals_arr[i]->kobj);
>  		kobject_put(&goals_arr[i]->kobj);
> +	}

[Severity: High]
This isn't a bug introduced by this patch, but since you are fixing missing
kobject_del() calls here to prevent name collisions, do the error paths in the
various *_add_dirs() functions need similar fixes?

If an error occurs after a successful kobject_init_and_add(), the error paths
currently call kobject_put() without kobject_del(). This can leave the sysfs
directory present until the object's reference count drops to zero and the
delayed release runs, potentially causing a -EEXIST failure if a user retries
the operation.

For example, looking at damon_sysfs_targets_add_dirs() in mm/damon/sysfs.c:

    err = damon_sysfs_target_add_dirs(target);
    if (err)
        goto out;
    ...
out:
    damon_sysfs_targets_rm_dirs(targets);
    kobject_put(&target->kobj);
    return err;

Could this leak the sysfs directory for target->kobj? 

The identical pattern appears in several other error paths:
- damon_sysfs_contexts_add_dirs() in mm/damon/sysfs.c
- damon_sysfs_kdamonds_add_dirs() in mm/damon/sysfs.c
- damon_sysfs_schemes_add_dirs() in mm/damon/sysfs-schemes.c
- damos_sysfs_populate_region_dir() in mm/damon/sysfs-schemes.c

>  	goals->nr = 0;
>  	kfree(goals_arr);
>  	goals->goals_arr = NULL;

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Sashiko AI review · https://sashiko.dev/#/patchset/20260616150844.88305-1-sj@kernel.org?part=6