Re: [RFC PATCH v1.1 02/11] mm/damon/sysfs: kobject_del() region and target (error) dirs

[sashiko-bot@kernel.org]

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

Pre-existing issues:
- [Medium] The patch series missed adding `kobject_del()` in the error path of `damon_sysfs_schemes_add_dirs()`. If `kobject_init_and_add()` succeeds but the subsequent `damon_sysfs_scheme_add_dirs()` fails, the code jumps to the `out:` label and calls `kobject_put(&scheme->kobj)` without first calling `kobject_del()`. Because the parent `schemes` directory persists, the failed scheme directory (e.g., '1') remains visible in sysfs until `CONFIG_DEBUG_KOBJECT_RELEASE` finally frees it. If userspace retries updating `nr_schemes`, it will fail with `-EEXIST`.
--

commit 58b8f68e38892e33bea755abf310672a0f0bb285
Author: SeongJae Park <sj@kernel.org>

mm/damon/sysfs: kobject_del() region and target (error) dirs

This commit fixes directory name conflicts caused by missing kobject_del() calls.
It ensures kobject_del() is called in the region directories removal path and
the target directories error path. This resolves failures when creating
directories with CONFIG_DEBUG_KOBJECT_RELEASE enabled.

Cc: <stable@vger.kernel.org> # 5.18.x

> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index dba1c67fc188f..3c349f0fe80f0 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c

[ ... ]

> @@ -372,13 +374,15 @@ static int damon_sysfs_targets_add_dirs(struct damon_sysfs_targets *targets,
>  
>  		err = damon_sysfs_target_add_dirs(target);
>  		if (err)
> -			goto out;
> +			goto del_out;
>  
>  		targets_arr[i] = target;
>  		targets->nr++;
>  	}
>  	return 0;
>  
> +del_out:
> +	kobject_del(&target->kobj);
>  out:
>  	damon_sysfs_targets_rm_dirs(targets);
>  	kobject_put(&target->kobj);

[Severity: Medium]
This is a pre-existing issue, but I noticed a similar pattern in
mm/damon/sysfs-schemes.c that seems to be missing a kobject_del() call.

In mm/damon/sysfs-schemes.c:damon_sysfs_schemes_add_dirs():

	err = kobject_init_and_add(&scheme->kobj,
			&damon_sysfs_scheme_ktype, &schemes->kobj,
			"%d", i);
	if (err)
		goto out;
	err = damon_sysfs_scheme_add_dirs(scheme);
	if (err)
		goto out;

	schemes_arr[i] = scheme;
	schemes->nr++;
}
return 0;

out:
	damon_sysfs_schemes_rm_dirs(schemes);
	kobject_put(&scheme->kobj);
	return err;

If damon_sysfs_scheme_add_dirs() fails after a successful
kobject_init_and_add(), we jump to out and call kobject_put() without first
calling kobject_del().

With CONFIG_DEBUG_KOBJECT_RELEASE enabled, could the persisting parent schemes
directory cause an -EEXIST conflict if userspace retries updating nr_schemes?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260617144807.91441-1-sj@kernel.org?part=2