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Message-ID: <17916824-ba97-68ba-8166-9402d5f4440c@openvz.org>
Date:   Tue, 28 Jun 2022 06:59:06 +0300
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Subject: Re: [PATCH cgroup] cgroup: set the correct return code if hierarchy
 limits are reached
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To:     Roman Gushchin <roman.gushchin@linux.dev>
Cc:     Shakeel Butt <shakeelb@google.com>,
        =?UTF-8?Q?Michal_Koutn=c3=bd?= <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
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 <d8a9e9c6-856e-1502-95ac-abf9700ff568@openvz.org> <YrpO9CUDt8hpUprr@castle>
From:   Vasily Averin <vvs@openvz.org>
In-Reply-To: <YrpO9CUDt8hpUprr@castle>
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On 6/28/22 03:44, Roman Gushchin wrote:
> 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.

I would agree with you, however in my opinion EAGAIN is used to restart an
interrupted system call. Thus, I worry its return can loop the user space without
any chance of continuation.

However, maybe I'm confusing something?

Thank you,
	Vasily Averin