Re: [PATCH 10/11] drm/amdkfd: Free queue in procfs_queue_type kobject release callback

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] sysfs: WARNING in kernfs_remove_by_name_ns due to unconditionally deleting uninitialized kobject
--

commit a813e5e5e38ff926a8859f22732d8fde3e0ed689
Author: Ian Rogers <irogers@google.com>

drm/amdkfd: Free queue in procfs_queue_type kobject release callback

This commit adds a release callback to free the struct queue from the kobject
release function to prevent a use-after-free, and adjusts the kobject_put()
locations accordingly.

> diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_process.c b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> --- a/drivers/gpu/drm/amd/amdkfd/kfd_process.c
> +++ b/drivers/gpu/drm/amd/amdkfd/kfd_process.c
[ ... ]
> @@ -701,7 +708,6 @@ void kfd_procfs_del_queue(struct queue *q)
>  		return;
>  
>  	kobject_del(&q->kobj);

[Severity: Medium]
Can this trigger a kernel warning if sysfs creation fails?

If kfd_procfs_add_queue() fails (for example, due to a memory allocation failure
in sysfs), q->kobj.state_in_sysfs remains 0 and q->kobj.sd is null. However,
pqm_create_queue() may ignore this sysfs failure and keep the queue operational.

Later, when pqm_destroy_queue() calls kfd_procfs_del_queue(), kobject_del() is
called unconditionally.

This results in a call chain to __kobject_del() which invokes
sysfs_remove_groups() with a null kobj->sd. This eventually propagates to
kernfs_remove_by_name_ns(), where a warning is triggered explicitly when
its parent argument is null:

fs/kernfs/dir.c:kernfs_remove_by_name_ns() {
    ...
    if (!parent) {
        WARN(1, KERN_WARNING "kernfs: can not remove '%s', no directory\n", name);
        return -ENOENT;
    }
    ...
}

Should we check if the kobject was successfully added to sysfs (such as checking
q->kobj.state_in_sysfs) before calling kobject_del()?

> -	kobject_put(&q->kobj);
>  }

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261013223946.1836757-1-irogers@google.com?part=10