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From:   Roman Gushchin <roman.gushchin@linux.dev>
To:     Vasily Averin <vvs@openvz.org>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
        Michal Hocko <mhocko@suse.com>, Tejun Heo <tj@kernel.org>,
        Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>, kernel@openvz.org,
        linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Vlastimil Babka <vbabka@suse.cz>,
        Muchun Song <songmuchun@bytedance.com>, cgroups@vger.kernel.org
Subject: Re: [PATCH cgroup] cgroup: set the correct return code if hierarchy
 limits are reached
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On Mon, Jun 27, 2022 at 05:12:55AM +0300, Vasily Averin wrote:
> When cgroup_mkdir reaches the limits of the cgroup hierarchy, it should
> not return -EAGAIN, but instead react similarly to reaching the global
> limit.
> 
> Signed-off-by: Vasily Averin <vvs@openvz.org>
> ---
>  kernel/cgroup/cgroup.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 1be0f81fe8e1..243239553ea3 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -5495,7 +5495,7 @@ int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode)
>  		return -ENODEV;
>  
>  	if (!cgroup_check_hierarchy_limits(parent)) {
> -		ret = -EAGAIN;
> +		ret = -ENOSPC;

I'd not argue whether ENOSPC is better or worse here, but I don't think we need
to change it now. It's been in this state for a long time and is a part of ABI.
EAGAIN is pretty unique as a mkdir() result, so systemd can handle it well.

Thanks!