Since v256 we completely fail to boot if v1 is configured. Fedora 41 was just
released with v256.7 and this is probably the first major exposure of users to
this code. It turns out not work very well. Fedora switched to v2 as default in
F31 (2019) and at that time some people added configuration to use v1 either
because of Docker or for other reasons. But it's been long enough ago that
people don't remember this and are now very unhappy when the system refuses to
boot after an upgrade.
Refusing to boot is also unnecessarilly punishing to users. For machines that
are used remotely, this could mean somebody needs to physically access the
machine. For other users, the machine might be the only way to access the net
and help, and people might not know how to set kernel parameters without some
docs. And because this is in systemd, after an upgrade all boot choices are
affected, and it's not possible to e.g. select an older kernel for boot. And
crashing the machine doesn't really serve our goal either: we were giving a
hint how to continue using v1 and nothing else.
If the new override is configured, warn and immediately boot to v1.
If v1 is configured w/o the override, warn and wait 30 s and boot to v2.
Also give a hint how to switch to v2.
https://bugzilla.redhat.com/show_bug.cgi?id=2323323https://bugzilla.redhat.com/show_bug.cgi?id=2323345https://bugzilla.redhat.com/show_bug.cgi?id=2322467https://www.reddit.com/r/Fedora/comments/1gfcyw9/refusing_to_run_under_cgroup_01_sy_specified_on/
The advice is to set systemd.unified_cgroup_hierarchy=1 (instead of removing
systemd.unified_cgroup_hierarchy=0). I think this is easier to convey. Users
who are understand what is going on can just remove the option instead.
The caching is dropped in cg_is_legacy_wanted(). It turns out that the
order in which those functions are called during early setup is very fragile.
If cg_is_legacy_wanted() is called before we have set up the v2 hierarchy,
we incorrectly cache a true answer. The function is called just a handful
of times at most, so we don't really need to cache the response.
When removing a cgroup, we always want to eliminate subcgroups
first, i.e. use cg_trim(). And cg_rmdir() (along with
CGROUP_REMOVE flag) is simply unused. Kill it.
THis brings the list of attributes to delegate to managers of subcgroups
to the state of kernel 6.6.
We probably should unify this list, and maybe generate it automatically
from /sys/kernel/cgroup/delegate, but let's do that another time.
systemd's own cgroup hierarchy is special to us, we use it to actually
manage processes. Because of that many calls tha apply to cgroups are
only ever called with the SYSTEMD_CGROUP_CONTROLLER as controller
argument. Let's hence remove the argument altogether.
This in particular touches the kill and xattr routines.
This changes no behaviour, we just drop an argument that is always set
to the same value anyway.
This is preparation to eventually getting rid of the cgroupvs1, because
on cgroupvs2 the cgroup paths do not change for different controllers,
there's only a single hierarchy there.
If we create a subcroup (regardless if the '.control' subgroup we
always created or one configured via DelegateSubgroup=) it's inside of
the delegated territory of the cgroup tree, hence it should be owned
fully by the unit's users. Hence do so.
IN C23, thread_local is a reserved keyword and we shall therefore
do nothing to redefine it. glibc has it defined for older standard
version with the right conditions.
v2 by Yu Watanabe:
Move the definition to missing_threads.h like the way we define e.g.
missing syscalls or missing definitions, and include it by the users.
Co-authored-by: Yu Watanabe <watanabe.yu+github@gmail.com>
Check if any cgroup controller is currently being used as v1, and if so don't
use cgroup unified mode. This is only checked when there is no cgroup already
mounted, and is most useful when running in a container where the host is using
a legacy or hybrid cgroup, since we can't (fully) use unified cgroup, as the
host kernel has the cgroup controllers in use by v1.
This shouldn't be needed if the container manager has pre-mounted cgroups
appropriately based on the host system cgroup setup, but we can't rely
on that always being the case.
Some masks shouldn't be needed externally, so keep their functions in
the module (others would fit there too but they're used in tests) to
think twice if something would depend on them.
Drop unused function cg_attach_many_everywhere.
Use cgroup_realized instead of cgroup_path when we actually ask for
realized.
This should not cause any functional changes.
When we are about to derealize a controller on v1 cgroup, we first
attempt to delete the controller cgroup and migrate afterwards. This
doesn't work in practice because populated cgroup cannot be deleted.
Furthermore, we leave out slices from migration completely, so
(un)setting a control value on them won't realize their controller
cgroup.
Rework actual realization, unit_create_cgroup() becomes
unit_update_cgroup() and make sure that controller hierarchies are
reduced when given controller cgroup ceased to be needed.
Note that with this we introduce slight deviation between v1 and v2 code
-- when a descendant unit turns off a delegated controller, we attempt
to disable it in ancestor slices. On v2 this may fail (kernel enforced,
because of child cgroups using the controller), on v1 we'll migrate
whole subtree and trim the subhierachy. (Previously, we wouldn't take
away delegated controller, however, derealization was broken anyway.)
Fixes: #14149
This way less stuff needs to be in basic. Initially, I wanted to move all the
parts of cgroup-utils.[ch] that depend on efivars.[ch] to shared, because
efivars.[ch] is in shared/. Later on, I decide to split efivars.[ch], so the
move done in this patch is not necessary anymore. Nevertheless, it is still
valid on its own. If at some point we want to expose libbasic, it is better to
to not have stuff that belong in libshared there.
Mike Yuan
Yu Watanabe
Nick Rosbrook
Zbigniew Jędrzejewski-Szmek
Timo Rothenpieler
Lennart Poettering
Cristian RodríguezandYu Watanabe
jiangchuangang
wineway
Dan Streetman
fangxiuning
Michal Koutný