diff --git a/pkg/controller/volume/persistentvolume/pv_controller.go b/pkg/controller/volume/persistentvolume/pv_controller.go
index 2002c62db4f..8ee7afdb329 100644
--- a/pkg/controller/volume/persistentvolume/pv_controller.go
+++ b/pkg/controller/volume/persistentvolume/pv_controller.go
@@ -346,7 +346,7 @@ func (ctrl *PersistentVolumeController) syncUnboundClaim(ctx context.Context, cl
 		}
 		if volume == nil {
 			logger.V(4).Info("Synchronizing unbound PersistentVolumeClaim, no volume found", "PVC", klog.KObj(claim))
-			// No PV could be found
+			// No PV could be found. Try to provision one if possible.
 			// OBSERVATION: pvc is "Pending", will retry
 
 			logger.V(4).Info("Attempting to assign storage class to unbound PersistentVolumeClaim", "PVC", klog.KObj(claim))
@@ -363,10 +363,15 @@ func (ctrl *PersistentVolumeController) syncUnboundClaim(ctx context.Context, cl
 
 			switch {
 			case delayBinding && !storagehelpers.IsDelayBindingProvisioning(claim):
+				// Scheduler does not observe any pod using this claim.
 				if err = ctrl.emitEventForUnboundDelayBindingClaim(claim); err != nil {
 					return err
 				}
 			case storagehelpers.GetPersistentVolumeClaimClass(claim) != "":
+				// The provisionClaim function may start a new asynchronous operation to provision a volume,
+				// or the operation is already running. The claim will be updated in the asynchronous operation,
+				// so the branch should be returned directly and the bind operation is expected to continue in
+				// the next sync loop.
 				if err = ctrl.provisionClaim(ctx, claim); err != nil {
 					return err
 				}