pkg/cri/server: optimizations in unmountRecursive()

thaJeztah · thaJeztah · commit 2374178c9b6b · 2021-01-08T17:32:01.000+01:00
Use a PrefixFilter() to get only the mounts we're interested in, which removes the need to manually filter mounts from the mountinfo results. Additional optimizations can be made, as: > ... there's a little known fact that `umount(MNT_DETACH)` is actually > recursive in Linux, IOW this function can be replaced with > `unix.Umount(target, unix.MNT_DETACH)` (or `mount.UnmountAll(target, unix.MNT_DETACH)` > (provided that target itself is a mount point). e8fb2c3#r535450446 Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
diff --git a/pkg/cri/server/helpers_linux.go b/pkg/cri/server/helpers_linux.go
@@ -166,34 +166,23 @@ func openLogFile(path string) (*os.File, error) {
 // unmountRecursive unmounts the target and all mounts underneath, starting with
 // the deepest mount first.
 func unmountRecursive(ctx context.Context, target string) error {
-	mounts, err := mountinfo.GetMounts(nil)
+	toUnmount, err := mountinfo.GetMounts(mountinfo.PrefixFilter(target))
 	if err != nil {
 		return err
 	}
 
-	var toUnmount []string
-	for _, m := range mounts {
-		p, err := filepath.Rel(target, m.Mountpoint)
-		if err != nil {
-			return err
-		}
-		if !strings.HasPrefix(p, "..") {
-			toUnmount = append(toUnmount, m.Mountpoint)
-		}
-	}
-
 	// Make the deepest mount be first
 	sort.Slice(toUnmount, func(i, j int) bool {
-		return len(toUnmount[i]) > len(toUnmount[j])
+		return len(toUnmount[i].Mountpoint) > len(toUnmount[j].Mountpoint)
 	})
 
-	for i, mountPath := range toUnmount {
-		if err := mount.UnmountAll(mountPath, unix.MNT_DETACH); err != nil {
+	for i, m := range toUnmount {
+		if err := mount.UnmountAll(m.Mountpoint, unix.MNT_DETACH); err != nil {
 			if i == len(toUnmount)-1 { // last mount
 				return err
 			}
 			// This is some submount, we can ignore this error for now, the final unmount will fail if this is a real problem
-			log.G(ctx).WithError(err).Debugf("failed to unmount submount %s", mountPath)
+			log.G(ctx).WithError(err).Debugf("failed to unmount submount %s", m.Mountpoint)
 		}
 	}
 	return nil
