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Check that cgroup is empty before deleting #228

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merged 3 commits into from
Oct 17, 2022
Merged

Check that cgroup is empty before deleting #228

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d695638
Check that cgroup is empty before deleting
jseba Apr 11, 2022
36ad4f7
call internal function to get processes that assumes lock is held
jseba Apr 12, 2022
6eb2c7a
add reason to live process error list for cgroupv1
jseba May 13, 2022
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12 changes: 11 additions & 1 deletion cgroup.go
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Original file line number Diff line number Diff line change
Expand Up @@ -84,7 +84,7 @@ func Load(hierarchy Hierarchy, path Path, opts ...InitOpts) (Cgroup, error) {
for _, s := range pathers(subsystems) {
p, err := path(s.Name())
if err != nil {
if errors.Is(err, os.ErrNotExist) {
if errors.Is(err, os.ErrNotExist) {
return nil, ErrCgroupDeleted
}
if err == ErrControllerNotActive {
Expand Down Expand Up @@ -228,6 +228,15 @@ func (c *cgroup) Delete() error {
}
var errs []string
for _, s := range c.subsystems {
// kernel prevents cgroups with running process from being removed, check the tree is empty
procs, err := c.processes(s.Name(), true, cgroupProcs)
if err != nil {
return err
}
if len(procs) > 0 {
errs = append(errs, fmt.Sprintf("%s (contains running processes)", string(s.Name())))
continue
}
if d, ok := s.(deleter); ok {
sp, err := c.path(s.Name())
if err != nil {
Expand All @@ -247,6 +256,7 @@ func (c *cgroup) Delete() error {
if err := remove(path); err != nil {
errs = append(errs, path)
}
continue
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is this continue necessary? I don't see how it changes loop flow since this is the end of the for and will naturally continue through the end of the range of subsystems.

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It's not strictly necessary, no. I added it to because from my interpretation of the structure of the code here, it's sort of like a switch case and only one branch should be valid, so if there was ever a third case (very unlikely since cgroup v1 is now legacy code), this would be correct for that situation.

Looking at it a bit more, I think it would be better if those two if blocks were restructured to better represent that intent that only one interface is expected to be matched. What do you think of something more like this, would that be more readable?

switch s.(type) {
case deleter:
    ...
case pather:
   ...
}

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continue looks okay to me to be honest. switch could work, but it couldn't have if len(procs) > 0 { case which is another continue case.

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@kzys kzys Oct 17, 2022 •
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Confirmed with @estesp offline that this is not a blocker.

}
}
if len(errs) > 0 {
Expand Down
8 changes: 8 additions & 0 deletions v2/manager.go
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Expand Up @@ -337,6 +337,14 @@ func (c *Manager) AddProc(pid uint64) error {
}

func (c *Manager) Delete() error {
// kernel prevents cgroups with running process from being removed, check the tree is empty
processes, err := c.Procs(true)
if err != nil {
return err
}
if len(processes) > 0 {
return fmt.Errorf("cgroups: unable to remove path %q: still contains running processes", c.path)
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Is it possible to have a similar message on cgroup.go?

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The v1 Delete just accumulates a list of subsystems that couldn't be removed and doesn't report the error. I could make the append more like:

errs = append(errs, fmt.Sprintf("%s (contains running processes)", string(s.Name()))

be a solution? Then the resulting error would be akin to

cgroups: unable to remove paths memory (contains running processes), cpu (contains running processes)

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sounds good to me!

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Apologies for not getting back to this sooner, I added the "contains running process" reason to the errors list in cgroup.go

}
return remove(c.path)
}

Expand Down