Remove unreturned locks, detect writes on closed heads

db.go

@@ -401,9 +401,8 @@ func (db *DB) Close() error {
 	close(db.stopc)
 	<-db.donec
 
-	// Lock mutex and leave it locked so we panic if there's a bug causing
-	// the block to be used afterwards.
 	db.mtx.Lock()
+	defer db.mtx.Unlock()
 
 	var g errgroup.Group
 

head.go

@@ -42,6 +42,7 @@ type headBlock struct {
 	wal        *WAL
 
 	activeWriters uint64
+	closed        bool
 
 	// descs holds all chunk descs for the head block. Each chunk implicitly
 	// is assigned the index as its ID.
@@ -137,9 +138,8 @@ func (h *headBlock) inBounds(t int64) bool {
 
 // Close syncs all data and closes underlying resources of the head block.
 func (h *headBlock) Close() error {
-	// Lock mutex and leave it locked so we panic if there's a bug causing
-	// the block to be used afterwards.
 	h.mtx.Lock()
+	defer h.mtx.Unlock()
 
 	if err := h.wal.Close(); err != nil {
 		return errors.Wrapf(err, "close WAL for head %s", h.dir)
@@ -156,6 +156,8 @@ func (h *headBlock) Close() error {
 	if meta.ULID == h.meta.ULID {
 		return writeMetaFile(h.dir, &h.meta)
 	}
+
+	h.closed = true
 	return nil
 }
 
@@ -175,6 +177,10 @@ func (h *headBlock) Appender() Appender {
 	atomic.AddUint64(&h.activeWriters, 1)
 
 	h.mtx.RLock()
+
+	if h.closed {
+		panic(fmt.Sprintf("block %s already closed", h.dir))
+	}
 	return &headAppender{headBlock: h, samples: getHeadAppendBuffer()}
 }
 

querier.go

@@ -66,6 +66,12 @@ func (s *DB) Querier(mint, maxt int64) Querier {
 
 		// TODO(fabxc): find nicer solution.
 		if hb, ok := b.(*headBlock); ok {
+			// TODO(fabxc): temporary refactored.
+			hb.mtx.RLock()
+			if hb.closed {
+				panic(fmt.Sprintf("block %s already closed", hb.dir))
+			}
+			hb.mtx.RUnlock()
 			q.postingsMapper = hb.remapPostings
 		}
 
@@ -135,15 +141,6 @@ type blockQuerier struct {
 	mint, maxt int64
 }
 
-func newBlockQuerier(ix IndexReader, c ChunkReader, mint, maxt int64) *blockQuerier {
-	return &blockQuerier{
-		mint:   mint,
-		maxt:   maxt,
-		index:  ix,
-		chunks: c,
-	}
-}
-
 func (q *blockQuerier) Select(ms ...labels.Matcher) SeriesSet {
 	var (
 		its    []Postings