metadata: hold lock on storageitem update

The locks usage is mixed up because two locks separate locks
are actually needed. With a specific lock, calls to SetValue
can be protected.

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

cache/metadata/metadata.go

@@ -205,10 +205,11 @@ func (s *Store) Close() error {
 
 type StorageItem struct {
 	id      string
+	vmu     sync.RWMutex
 	values  map[string]*Value
+	qmu     sync.Mutex
 	queue   []func(*bolt.Bucket) error
 	storage *Store
-	mu      sync.RWMutex
 }
 
 func newStorageItem(id string, b *bolt.Bucket, s *Store) (*StorageItem, error) {
@@ -242,10 +243,6 @@ func (s *StorageItem) ID() string {
 	return s.id
 }
 
-func (s *StorageItem) View(fn func(b *bolt.Bucket) error) error {
-	return s.storage.View(s.id, fn)
-}
-
 func (s *StorageItem) Update(fn func(b *bolt.Bucket) error) error {
 	return s.storage.Update(s.id, fn)
 }
@@ -255,17 +252,19 @@ func (s *StorageItem) Metadata() *StorageItem {
 }
 
 func (s *StorageItem) Keys() []string {
+	s.vmu.RLock()
 	keys := make([]string, 0, len(s.values))
 	for k := range s.values {
 		keys = append(keys, k)
 	}
+	s.vmu.RUnlock()
 	return keys
 }
 
 func (s *StorageItem) Get(k string) *Value {
-	s.mu.RLock()
+	s.vmu.RLock()
 	v := s.values[k]
-	s.mu.RUnlock()
+	s.vmu.RUnlock()
 	return v
 }
 
@@ -310,14 +309,14 @@ func (s *StorageItem) SetExternal(k string, dt []byte) error {
 }
 
 func (s *StorageItem) Queue(fn func(b *bolt.Bucket) error) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
+	s.qmu.Lock()
+	defer s.qmu.Unlock()
 	s.queue = append(s.queue, fn)
 }
 
 func (s *StorageItem) Commit() error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
+	s.qmu.Lock()
+	defer s.qmu.Unlock()
 	return errors.WithStack(s.Update(func(b *bolt.Bucket) error {
 		for _, fn := range s.queue {
 			if err := fn(b); err != nil {
@@ -330,15 +329,23 @@ func (s *StorageItem) Commit() error {
 }
 
 func (s *StorageItem) Indexes() (out []string) {
+	s.vmu.RLock()
 	for _, v := range s.values {
 		if v.Index != "" {
 			out = append(out, v.Index)
 		}
 	}
+	s.vmu.RUnlock()
 	return
 }
 
 func (s *StorageItem) SetValue(b *bolt.Bucket, key string, v *Value) error {
+	s.vmu.Lock()
+	defer s.vmu.Unlock()
+	return s.setValue(b, key, v)
+}
+
+func (s *StorageItem) setValue(b *bolt.Bucket, key string, v *Value) error {
 	if v == nil {
 		if old, ok := s.values[key]; ok {
 			if old.Index != "" {
@@ -378,16 +385,16 @@ func (s *StorageItem) SetValue(b *bolt.Bucket, key string, v *Value) error {
 var ErrSkipSetValue = errors.New("skip setting metadata value")
 
 func (s *StorageItem) GetAndSetValue(key string, fn func(*Value) (*Value, error)) error {
-	s.mu.Lock()
-	defer s.mu.Unlock()
 	return s.Update(func(b *bolt.Bucket) error {
+		s.vmu.Lock()
+		defer s.vmu.Unlock()
 		v, err := fn(s.values[key])
 		if errors.Is(err, ErrSkipSetValue) {
 			return nil
 		} else if err != nil {
 			return err
 		}
-		return s.SetValue(b, key, v)
+		return s.setValue(b, key, v)
 	})
 }