backend: getting lock before accessing db

storage/backend/backend.go

@@ -205,11 +205,9 @@ func (b *backend) Defrag() error {
 	// lock batchTx to ensure nobody is using previous tx, and then
 	// close previous ongoing tx.
 	b.batchTx.Lock()
-	defer b.batchTx.Unlock()
 
 	// lock database after lock tx to avoid deadlock.
 	b.mu.Lock()
-	defer b.mu.Unlock()
 
 	b.batchTx.commit(true)
 	b.batchTx.tx = nil
@@ -251,8 +249,11 @@ func (b *backend) Defrag() error {
 	if err != nil {
 		log.Fatalf("backend: cannot begin tx (%s)", err)
 	}
+
+	b.batchTx.Unlock()
+	b.mu.Unlock()
 	// commit to update metadata like db.size
-	b.batchTx.commit(false)
+	b.ForceCommit()
 
 	return nil
 }

storage/backend/batch_tx.go

@@ -160,6 +160,8 @@ func (t *batchTx) commit(stop bool) {
 	// commit the last tx
 	if t.tx != nil {
 		if t.pending == 0 && !stop {
+			t.backend.mu.RLock()
+			defer t.backend.mu.RUnlock()
 			atomic.StoreInt64(&t.backend.size, t.tx.Size())
 			return
 		}