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    SubjectRe: [PATCH cgroup] cgroup: set the correct return code if hierarchy limits are reached
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    On 6/28/22 12:22, Tejun Heo wrote:
    > On Tue, Jun 28, 2022 at 11:16:48AM +0200, Michal Koutný wrote:
    >> The mkdir(2) manpage doesn't list EAGAIN at all. ENOSPC makes better
    >> sense here. (And I suspect the dependency on this particular value won't
    >> be very wide spread.)
    >
    > Given how we use these system calls as triggers for random kernel
    > operations, I don't think adhering to posix standard is necessary or
    > possible. Using an error code which isn't listed in the man page isn't
    > particularly high in the list of discrepancies.
    >
    > Again, I'm not against changing it but I'd like to see better
    > rationales. On one side, we have "it's been this way for a long time
    > and there's nothing particularly broken about it". I'm not sure the
    > arguments we have for the other side is strong enough yet.

    I would like to recall this patch.

    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

    Thank you,
    Vasily Averin

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