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Sender: Tejun Heo <htejun@gmail.com>
Date:   Thu, 30 Jun 2022 04:25:57 +0900
From:   Tejun Heo <tj@kernel.org>
To:     Vasily Averin <vvs@openvz.org>
Cc:     Michal =?iso-8859-1?Q?Koutn=FD?= <mkoutny@suse.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Shakeel Butt <shakeelb@google.com>,
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        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 Wed, Jun 29, 2022 at 09:13:02AM +0300, Vasily Averin wrote:
> I experimented on fedora36 node with LXC and centos stream 9 container.
> and I did not noticed any critical systemd troubles with original -EAGAIN.
> When cgroup's limit is reached systemd cannot start new services, 
> for example lxc-attach generates following output:
> 
> [root@fc34-vvs ~]# lxc-attach c9s
> lxc-attach: c9s: cgroups/cgfsng.c: cgroup_attach_leaf: 2084 Resource temporarily unavailable - Failed to create leaf cgroup ".lxc"
> lxc-attach: c9s: cgroups/cgfsng.c: __cgroup_attach_many: 3517 Resource temporarily unavailable - Failed to attach to cgroup fd 11
> lxc-attach: c9s: attach.c: lxc_attach: 1679 Resource temporarily unavailable - Failed to attach cgroup
> lxc-attach: c9s: attach.c: do_attach: 1237 No data available - Failed to receive lsm label fd
> lxc-attach: c9s: attach.c: do_attach: 1375 Failed to attach to container
> 
> I did not found any loop in userspace caused by EAGAIN.
> Messages looks unclear, however situation with the patched kernel is not much better:
> 
> [root@fc34-vvs ~]# lxc-attach c9s
> lxc-attach: c9s: cgroups/cgfsng.c: cgroup_attach_leaf: 2084 No space left on device - Failed to create leaf cgroup ".lxc"
> lxc-attach: c9s: cgroups/cgfsng.c: __cgroup_attach_many: 3517 No space left on device - Failed to attach to cgroup fd 11
> lxc-attach: c9s: attach.c: lxc_attach: 1679 No space left on device - Failed to attach cgroup
> lxc-attach: c9s: attach.c: do_attach: 1237 No data available - Failed to receive lsm label fd
> lxc-attach: c9s: attach.c: do_attach: 1375 Failed to attach to container

I'd say "resource temporarily unavailable" is better fitting than "no
space left on device" and the syscall restart thing isn't handled by
-EAGAIN return value. Grep restart_block for that.

Thanks.

-- 
tejun