linux-kernel - Re: [PATCH cgroup] cgroup: set the correct return code if hierarchy limits are reached

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Date:   Thu, 30 Jun 2022 19:42:36 -0700
From:   Roman Gushchin <roman.gushchin@...ux.dev>
To:     Tejun Heo <tj@...nel.org>
Cc:     Vasily Averin <vvs@...nvz.org>,
        Michal Koutný <mkoutny@...e.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...e.com>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>, kernel@...nvz.org,
        linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Vlastimil Babka <vbabka@...e.cz>,
        Muchun Song <songmuchun@...edance.com>, cgroups@...r.kernel.org
Subject: Re: [PATCH cgroup] cgroup: set the correct return code if hierarchy
 limits are reached

On Thu, Jun 30, 2022 at 04:25:57AM +0900, Tejun Heo wrote:
> 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@...4-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@...4-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"

+1

Thanks!