From 6df7bae9aedaa97c0ab25ebd4f11abd2638cb864 Mon Sep 17 00:00:00 2001 From: lifubang Date: Sat, 5 Jul 2025 00:25:01 +0000 Subject: [PATCH] fs2: ignore no device error when reading freezer state MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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. Unfortunately, the second case was accidentally removed during a code refactoring. We should add it back to ensure correct error handling. Signed-off-by: lifubang --- fs2/freezer.go | 32 ++++++++++++++++++++++++-------- 1 file changed, 24 insertions(+), 8 deletions(-) diff --git a/fs2/freezer.go b/fs2/freezer.go index f0192f0..6307e68 100644 --- a/fs2/freezer.go +++ b/fs2/freezer.go @@ -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() @@ -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": @@ -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) { + 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)