Previously, unit_{start,stop,reload} would call the low-level cgroup
unfreeze function whenever a unit was started, stopped, or reloaded. It
did so with no error checking. This call would ultimately recurse up the
cgroup tree, and unfreeze all the parent cgroups of the unit, unless an
error occurred (in which case I have no idea what would happen...)
After the freeze/thaw rework in a previous commit, this can no longer
work. If we recursively thaw the parent cgroups of the unit, there may
be sibling units marked as PARENT_FROZEN which will no longer actually
have frozen parents. Fixing this is a lot more complicated than simply
disallowing start/stop/reload on a frozen unit
Fixes https://github.com/systemd/systemd/issues/15849
This commit overhauls the way freeze/thaw works recursively:
First, it introduces new FreezerActions that are like the existing
FREEZE and THAW but indicate that the action was initiated by a parent
unit. We also refactored the code to pass these FreezerActions through
the whole call stack so that we can make use of them. FreezerState was
extended similarly, to be able to differentiate between a unit that's
frozen manually and a unit that's frozen because a parent is frozen.
Next, slices were changed to check recursively that all their child
units can be frozen before it attempts to freeze them. This is different
from the previous behavior, that would just check if the unit's type
supported freezing at all. This cleans up the code, and also ensures
that the behavior of slices corresponds to the unit's actual ability
to be frozen
Next, we make it so that if you FREEZE a slice, it'll PARENT_FREEZE
all of its children. Similarly, if you THAW a slice it will PARENT_THAW
its children.
Finally, we use the new states available to us to refactor the code
that actually does the cgroup freezing. The code now looks at the unit's
existing freezer state and the action being requested, and decides what
next state is most appropriate. Then it puts the unit in that state.
For instance, a RUNNING unit with a request to PARENT_FREEZE will
put the unit into the PARENT_FREEZING state. As another example, a
FROZEN unit who's parent is also FROZEN will transition to
PARENT_FROZEN in response to a request to THAW.
Fixes https://github.com/systemd/systemd/issues/30640
Fixes https://github.com/systemd/systemd/issues/15850
Let's keep the debug logs in the journal, while logging only
testsute-*.sh stdout/stderr to the console (ba7abf7). This should make
the test output log a bit more readable and potentially the tests itself
a bit faster by avoiding console oversaturation.
Also, it should significantly reduce the size of artifacts kept by CIs.
When checking the unit state after `systemctl freeze|thaw` we can be
"too fast" and get the intermediate state (freezing/thawing) which we're
not interested in. Let's wait a bit and try to get the state again in
such cases to avoid unnecessary flakiness.
```
[ 29.390203] testsuite-38.sh[218]: + state=thawing
[ 29.390203] testsuite-38.sh[218]: + '[' thawing = running ']'
[ 29.390203] testsuite-38.sh[218]: + echo 'error: unexpected freezer state, expected: running, actual: thawing'
[ 29.390203] testsuite-38.sh[218]: error: unexpected freezer state, expected: running, actual: thawing
[ 29.390203] testsuite-38.sh[218]: + exit 1
```
Adrian Vovk
Frantisek Sumsal
Zbigniew Jędrzejewski-Szmek
Michal Sekletár