Re: [RFC PATCH 9/9] mm/damon/sysfs: kobject_del() probe 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 adds `kobject_del()` to `damon_sysfs_probes_rm_dirs()` to fix sysfs name collisions caused by delayed kobject releases, but misses the exact same flaw on the error paths of `damon_sysfs_probes_add_dirs()` and multiple other array-building functions. This leaves the system vulnerable to `-EEXIST` failures upon retry after an error.
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commit 4a5efc2733f009261a15fd64a4d901ca19499bb5
Author: SeongJae Park <sj@kernel.org>

mm/damon/sysfs: kobject_del() probe dirs

This commit fixes a directory creation failure caused by name conflicts
when CONFIG_DEBUG_KOBJECT_RELEASE is enabled. It adds missing kobject_del()
calls during the removal of probe directories.

> diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
> index 04725ff3d9f3c..04ca0a34e1206 100644
> --- a/mm/damon/sysfs.c
> +++ b/mm/damon/sysfs.c
> @@ -1139,6 +1139,7 @@ static void damon_sysfs_probes_rm_dirs(
>  
>  	for (i = 0; i < probes->nr; i++) {
>  		damon_sysfs_probe_rm_dirs(probes_arr[i]);
> +		kobject_del(&probes_arr[i]->kobj);

[Severity: Medium]
This is a pre-existing issue, but it looks like the same lack of
kobject_del() on error paths could cause name collisions upon retry.

For example, if damon_sysfs_probe_add_dirs() fails inside
damon_sysfs_probes_add_dirs(), the error path drops the probe by calling
kobject_put() without kobject_del():

mm/damon/sysfs.c:damon_sysfs_probes_add_dirs() {
    ...
		err = damon_sysfs_probe_add_dirs(probe);
		if (err) {
			kobject_put(&probe->kobj);
			damon_sysfs_probes_rm_dirs(probes);
			return err;
		}
    ...
}

Under CONFIG_DEBUG_KOBJECT_RELEASE, if userspace immediately retries the
operation after an error, won't kobject_init_and_add() fail with -EEXIST due
to a name collision with the lingering directory?

Should we also add synchronous sysfs deletion via kobject_del() to these
similar error paths?
- mm/damon/sysfs.c:damon_sysfs_targets_add_dirs()
- mm/damon/sysfs.c:damon_sysfs_contexts_add_dirs()
- mm/damon/sysfs.c:damon_sysfs_kdamonds_add_dirs()
- mm/damon/sysfs-schemes.c:damon_sysfs_schemes_add_dirs()

>  		kobject_put(&probes_arr[i]->kobj);
>  	}
>  	probes->nr = 0;

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616150844.88305-1-sj@kernel.org?part=9