Call WaitGroup.Done() once only when PVB changes to final status the first time to avoid panic

Prevents calling WaitGroup.Done() multiple times for the same PodVolumeBackup by
tracking processed PVBs. This avoids "negative WaitGroup counter" panic errors when
the handler receives multiple update events with the PVB already in final status.

Based on upstream commit 2eb97fa
Adapted for OADP 1.4 without pvbIndexer infrastructure

Signed-off-by: Tiger Kaovilai <tkaovilai@redhat.com>

Author: kaovilai

pkg/podvolume/backupper.go

@@ -58,6 +58,7 @@ type backupper struct {
 	handlerRegistration cache.ResourceEventHandlerRegistration
 	wg                  sync.WaitGroup
 	result              []*velerov1api.PodVolumeBackup
+	processedPVBs       sync.Map // tracks PVBs that have already been processed to avoid calling Done() multiple times
 }
 
 type skippedPVC struct {
@@ -109,14 +110,15 @@ func newBackupper(
 	backup *velerov1api.Backup,
 ) *backupper {
 	b := &backupper{
-		ctx:          ctx,
-		repoLocker:   repoLocker,
-		repoEnsurer:  repoEnsurer,
-		crClient:     crClient,
-		uploaderType: uploaderType,
-		pvbInformer:  pvbInformer,
-		wg:           sync.WaitGroup{},
-		result:       []*velerov1api.PodVolumeBackup{},
+		ctx:           ctx,
+		repoLocker:    repoLocker,
+		repoEnsurer:   repoEnsurer,
+		crClient:      crClient,
+		uploaderType:  uploaderType,
+		pvbInformer:   pvbInformer,
+		wg:            sync.WaitGroup{},
+		result:        []*velerov1api.PodVolumeBackup{},
+		processedPVBs: sync.Map{},
 	}
 
 	b.handlerRegistration, _ = pvbInformer.AddEventHandler(
@@ -133,8 +135,16 @@ func newBackupper(
 					return
 				}
 
-				b.result = append(b.result, pvb)
-				b.wg.Done()
+				// Generate a unique key for this PVB
+				pvbKey := pvb.Namespace + "/" + pvb.Name
+				
+				// Check if we've already processed this PVB in final status
+				// This prevents calling WaitGroup.Done() multiple times for the same PVB
+				// which could happen if the handler receives multiple update events with the PVB already in final status
+				if _, alreadyProcessed := b.processedPVBs.LoadOrStore(pvbKey, true); !alreadyProcessed {
+					b.result = append(b.result, pvb)
+					b.wg.Done()
+				}
 			},
 		},
 	)