layer: protect mountedLayer.references

Add a mutex to protect concurrent access to mountedLayer.references map.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

layer/mounted_layer.go

@@ -2,6 +2,7 @@ package layer // import "github.com/docker/docker/layer"
 
 import (
 	"io"
+	"sync"
 
 	"github.com/docker/docker/pkg/archive"
 	"github.com/docker/docker/pkg/containerfs"
@@ -15,6 +16,7 @@ type mountedLayer struct {
 	path       string
 	layerStore *layerStore
 
+	sync.Mutex
 	references map[RWLayer]*referencedRWLayer
 }
 
@@ -62,16 +64,24 @@ func (ml *mountedLayer) getReference() RWLayer {
 	ref := &referencedRWLayer{
 		mountedLayer: ml,
 	}
+	ml.Lock()
 	ml.references[ref] = ref
+	ml.Unlock()
 
 	return ref
 }
 
 func (ml *mountedLayer) hasReferences() bool {
-	return len(ml.references) > 0
+	ml.Lock()
+	ret := len(ml.references) > 0
+	ml.Unlock()
+
+	return ret
 }
 
 func (ml *mountedLayer) deleteReference(ref RWLayer) error {
+	ml.Lock()
+	defer ml.Unlock()
 	if _, ok := ml.references[ref]; !ok {
 		return ErrLayerNotRetained
 	}
@@ -81,7 +91,9 @@ func (ml *mountedLayer) deleteReference(ref RWLayer) error {
 
 func (ml *mountedLayer) retakeReference(r RWLayer) {
 	if ref, ok := r.(*referencedRWLayer); ok {
+		ml.Lock()
 		ml.references[ref] = ref
+		ml.Unlock()
 	}
 }