light: fix light store deadlock (#5901)

light/store/db/db.go

@@ -243,12 +243,14 @@ func (s *dbs) Prune(size uint16) error {
 	b := s.db.NewBatch()
 	defer b.Close()
 
+	var pruned uint16 = 0
 	for itr.Valid() && numToPrune > 0 {
 		if err = b.Delete(itr.Key()); err != nil {
 			return err
 		}
 		itr.Next()
 		numToPrune--
+		pruned++
 	}
 	if err = itr.Error(); err != nil {
 		return err
@@ -256,11 +258,12 @@ func (s *dbs) Prune(size uint16) error {
 
 	// 3) // update size
 	s.mtx.Lock()
-	s.size = size
+	s.size -= pruned
+	newSize := s.size
 	s.mtx.Unlock()
 
-	if wErr := b.Set(s.sizeKey(), marshalSize(size)); wErr != nil {
-		return fmt.Errorf("failed to persist size: %w", wErr)
+	if err := b.Set(s.sizeKey(), marshalSize(newSize)); err != nil {
+		return fmt.Errorf("failed to persist size: %w", err)
 	}
 
 	// 4) write batch deletion to disk

light/store/db/db_test.go

@@ -148,6 +148,13 @@ func Test_Concurrency(t *testing.T) {
 				t.Log(err)
 			}
 
+			if i > 2 {
+				_, err = dbStore.LightBlockBefore(i - 1)
+				if err != nil {
+					t.Log(err)
+				}
+			}
+
 			_, err = dbStore.LastLightBlockHeight()
 			if err != nil {
 				t.Log(err)
@@ -157,16 +164,19 @@ func Test_Concurrency(t *testing.T) {
 				t.Log(err)
 			}
 
-			err = dbStore.Prune(2)
+			err = dbStore.Prune(3)
 			if err != nil {
 				t.Log(err)
 			}
 			_ = dbStore.Size()
 
-			err = dbStore.DeleteLightBlock(1)
-			if err != nil {
-				t.Log(err)
+			if i > 2 && i%2 == 0 {
+				err = dbStore.DeleteLightBlock(i - 1)
+				if err != nil {
+					t.Log(err)
+				}
 			}
+
 		}(int64(i))
 	}