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libct/cg/fs/freezer: make sure to thaw on failure #2918

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merged 1 commit into from Apr 21, 2021
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libct/cg/fs/freezer: make sure to thaw on failure #2918

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libct/cg/fs/freezer: make sure to thaw on failure 
Function (*FreezerGroup).Set has a few paths where in can return an
error. In any case, if an error is returned, we failed to freeze,
and we need to thaw to avoid leaving the cgroup in a stuck state.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
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@kolyshkin
kolyshkin committed Apr 20, 2021
commit fcd7fe85e1ea706fbdfb383824e9f390a53a34e9
14 changes: 10 additions & 4 deletions libcontainer/cgroups/fs/freezer.go
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Expand Up @@ -27,9 +27,18 @@ func (s *FreezerGroup) Apply(path string, d *cgroupData) error {
return join(path, d.pid)
}

func (s *FreezerGroup) Set(path string, cgroup *configs.Cgroup) error {
func (s *FreezerGroup) Set(path string, cgroup *configs.Cgroup) (Err error) {
switch cgroup.Resources.Freezer {
case configs.Frozen:
defer func() {
if Err != nil {
// Freezing failed, and it is bad and dangerous
// to leave the cgroup in FROZEN or FREEZING
// state, so (try to) thaw it back.
_ = fscommon.WriteFile(path, "freezer.state", string(configs.Thawed))
}
}()

// As per older kernel docs (freezer-subsystem.txt before
// kernel commit ef9fe980c6fcc1821), if FREEZING is seen,
// userspace should either retry or thaw. While current
Expand Down Expand Up @@ -75,9 +84,6 @@ func (s *FreezerGroup) Set(path string, cgroup *configs.Cgroup) error {
}
}
// Despite our best efforts, it got stuck in FREEZING.
// Leaving it in this state is bad and dangerous, so
// let's (try to) thaw it back and error out.
_ = fscommon.WriteFile(path, "freezer.state", string(configs.Thawed))
return errors.New("unable to freeze")
case configs.Thawed:
return fscommon.WriteFile(path, "freezer.state", string(configs.Thawed))
Expand Down