UnmountIpcMount: simplify

As standard mount.Unmount does what we need, let's use it.

In addition, this adds ignoring "not mounted" condition, which
was previously implemented (see PR#33329, commit cfa2591d3f26)
via a very expensive call to mount.Mounted().

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

container/container_unix.go

@@ -174,8 +174,8 @@ func (container *Container) HasMountFor(path string) bool {
 	return false
 }
 
-// UnmountIpcMount uses the provided unmount function to unmount shm if it was mounted
-func (container *Container) UnmountIpcMount(unmount func(pth string) error) error {
+// UnmountIpcMount unmounts shm if it was mounted
+func (container *Container) UnmountIpcMount() error {
 	if container.HasMountFor("/dev/shm") {
 		return nil
 	}
@@ -189,10 +189,8 @@ func (container *Container) UnmountIpcMount(unmount func(pth string) error) erro
 	if shmPath == "" {
 		return nil
 	}
-	if err = unmount(shmPath); err != nil && !os.IsNotExist(err) {
-		if mounted, mErr := mount.Mounted(shmPath); mounted || mErr != nil {
-			return errors.Wrapf(err, "umount %s", shmPath)
-		}
+	if err = mount.Unmount(shmPath); err != nil && !os.IsNotExist(err) {
+		return errors.Wrapf(err, "umount %s", shmPath)
 	}
 	return nil
 }

container/container_windows.go

@@ -22,7 +22,7 @@ const (
 
 // UnmountIpcMount unmounts Ipc related mounts.
 // This is a NOOP on windows.
-func (container *Container) UnmountIpcMount(unmount func(pth string) error) error {
+func (container *Container) UnmountIpcMount() error {
 	return nil
 }
 

daemon/container_operations_unix.go

@@ -351,10 +351,6 @@ func killProcessDirectly(cntr *container.Container) error {
 	return nil
 }
 
-func detachMounted(path string) error {
-	return unix.Unmount(path, unix.MNT_DETACH)
-}
-
 func isLinkable(child *container.Container) bool {
 	// A container is linkable only if it belongs to the default network
 	_, ok := child.NetworkSettings.Networks[runconfig.DefaultDaemonNetworkMode().NetworkName()]

daemon/container_operations_windows.go

@@ -78,10 +78,6 @@ func (daemon *Daemon) mountVolumes(container *container.Container) error {
 	return nil
 }
 
-func detachMounted(path string) error {
-	return nil
-}
-
 func (daemon *Daemon) setupSecretDir(c *container.Container) (setupErr error) {
 	if len(c.SecretReferences) == 0 {
 		return nil

daemon/start.go

@@ -216,7 +216,7 @@ func (daemon *Daemon) containerStart(container *container.Container, checkpoint
 func (daemon *Daemon) Cleanup(container *container.Container) {
 	daemon.releaseNetwork(container)
 
-	if err := container.UnmountIpcMount(detachMounted); err != nil {
+	if err := container.UnmountIpcMount(); err != nil {
 		logrus.Warnf("%s cleanup: failed to unmount IPC: %s", container.ID, err)
 	}