Add LockVolumeWithSnapshot function to prevent future deadlocks

Signed-off-by: Luca Berneking <l.berneking@mittwald.de>

pkg/driver/controller.go

@@ -75,6 +75,15 @@ func (cs *controller) LockVolume(volume string) func() {
 	return func() { mtx.Unlock() }
 }
 
+func (cs *controller) LockVolumeWithSnapshot(volume string, snapshot string) func() {
+	unlockVol := cs.LockVolume(volume)
+	unlockSnap := cs.LockVolume(snapshot)
+	return func() {
+		unlockVol()
+		unlockSnap()
+	}
+}
+
 // NewController returns a new instance
 // of CSI controller
 func NewController(d *CSIDriver) csi.ControllerServer {
@@ -722,10 +731,8 @@ func (cs *controller) CreateSnapshot(
 	if err != nil {
 		return nil, err
 	}
-	unlockVol := cs.LockVolume(volumeID)
-	defer unlockVol()
-	unlockSnap := cs.LockVolume(snapName)
-	defer unlockSnap()
+	unlock := cs.LockVolumeWithSnapshot(volumeID, snapName)
+	defer unlock()
 
 	snapTimeStamp := time.Now().Unix()
 	var state string
@@ -822,10 +829,8 @@ func (cs *controller) DeleteSnapshot(
 		// should succeed when an invalid snapshot id is used
 		return &csi.DeleteSnapshotResponse{}, nil
 	}
-	unlockVol := cs.LockVolume(snapshotID[0])
-	defer unlockVol()
-	unlockSnap := cs.LockVolume(snapshotID[1])
-	defer unlockSnap()
+	unlock := cs.LockVolumeWithSnapshot(snapshotID[0], snapshotID[1])
+	defer unlock()
 	if err := zfs.DeleteSnapshot(snapshotID[1]); err != nil {
 		return nil, status.Errorf(
 			codes.Internal,