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fs2: ignore no device error when reading freezer state #25

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Merged
kolyshkin merged 1 commit into from
Jul 14, 2025
Merged

fs2: ignore no device error when reading freezer state #25

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32 changes: 24 additions & 8 deletions fs2/freezer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -53,12 +53,9 @@ func setFreezer(dirPath string, state cgroups.FreezerState) error {
func getFreezer(dirPath string) (cgroups.FreezerState, error) {
fd, err := cgroups.OpenFile(dirPath, "cgroup.freeze", unix.O_RDONLY)
if err != nil {
// If the kernel is too old, then we just treat the freezer as being in
// an "undefined" state.
if os.IsNotExist(err) || errors.Is(err, unix.ENODEV) {
err = nil
}
return cgroups.Undefined, err
// If the kernel is too old, then we just treat the freezer as
// being in an "undefined" state and ignore the error.
return cgroups.Undefined, ignoreNotExistOrNoDeviceError(err)
}
defer fd.Close()

Expand All @@ -67,11 +64,15 @@ func getFreezer(dirPath string) (cgroups.FreezerState, error) {

func readFreezer(dirPath string, fd *os.File) (cgroups.FreezerState, error) {
if _, err := fd.Seek(0, 0); err != nil {
return cgroups.Undefined, err
// If the cgroup path is deleted at this point, then we just treat the freezer as
// being in an "undefined" state and ignore the error.
return cgroups.Undefined, ignoreNotExistOrNoDeviceError(err)
}
state := make([]byte, 2)
if _, err := fd.Read(state); err != nil {
return cgroups.Undefined, err
// If the cgroup path is deleted at this point, then we just treat the freezer as
// being in an "undefined" state and ignore the error.
return cgroups.Undefined, ignoreNotExistOrNoDeviceError(err)
}
switch string(state) {
case "0\n":
Expand All @@ -83,6 +84,21 @@ func readFreezer(dirPath string, fd *os.File) (cgroups.FreezerState, error) {
}
}

// ignoreNotExistOrNoDeviceError checks if the error is either a "not exist" error
// or a "no device" error, and returns nil in those cases. Otherwise, it returns the error.
func ignoreNotExistOrNoDeviceError(err error) error {
// We can safely ignore the error in the following two common situations:
// 1. The cgroup path does not exist at the time of opening(eg: the kernel is too old)
// — indicated by os.IsNotExist.
// 2. The cgroup path is deleted during the seek/read operation — indicated by
// errors.Is(err, unix.ENODEV).
// These conditions are expected and do not require special handling.
if os.IsNotExist(err) || errors.Is(err, unix.ENODEV) {
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@thaJeztah thaJeztah Jul 14, 2025

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Do you think we need to call out that we're deliberately using os.IsNotExist() here, instead of errors.Is (https://pkg.go.dev/os#IsNotExist) to prevent someone from updating the code, or would we be paying attention if that would happen?

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@kolyshkin kolyshkin Jul 14, 2025

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Let's address this as a followup.

return nil
}
return err
}

// waitFrozen polls cgroup.events until it sees "frozen 1" in it.
func waitFrozen(dirPath string) (cgroups.FreezerState, error) {
fd, err := cgroups.OpenFile(dirPath, "cgroup.events", unix.O_RDONLY)
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