[#728] writecache: Fix Badger writecache race.

Signed-off-by: Dmitrii Stepanov <d.stepanov@yadro.com>

pkg/local_object_storage/writecache/writecachebadger/cachebadger.go

@@ -85,6 +85,9 @@ func (c *cache) DumpInfo() writecache.Info {
 
 // Open opens and initializes database. Reads object counters from the ObjectCounters instance.
 func (c *cache) Open(_ context.Context, readOnly bool) error {
+	c.modeMtx.Lock()
+	defer c.modeMtx.Unlock()
+
 	err := c.openStore(readOnly)
 	if err != nil {
 		return metaerr.Wrap(err)
@@ -94,6 +97,9 @@ func (c *cache) Open(_ context.Context, readOnly bool) error {
 
 // Init runs necessary services.
 func (c *cache) Init() error {
+	c.modeMtx.Lock()
+	defer c.modeMtx.Unlock()
+
 	c.log.Info(logs.WritecacheBadgerInitExperimental)
 	c.metrics.SetMode(c.mode)
 	ctx, cancel := context.WithCancel(context.Background())

pkg/local_object_storage/writecache/writecachebadger/gc.go

@@ -21,12 +21,20 @@ func (c *cache) runGCLoop(ctx context.Context) {
 			case <-ctx.Done():
 				return
 			case <-t.C:
+				c.runGC()
+			}
+		}
+	}()
+}
+
+func (c *cache) runGC() {
 	// This serves to synchronize the c.db field when changing mode as well.
 	c.modeMtx.RLock()
+	defer c.modeMtx.RUnlock()
+
 	ro := c.readOnly()
-				c.modeMtx.RUnlock()
 	if ro {
-					continue
+		return
 	}
 
 	// 0.5 is the recommended value so that write amplification of the value log is 2.
@@ -35,6 +43,3 @@ func (c *cache) runGCLoop(ctx context.Context) {
 		c.log.Debug(logs.WritecacheDBValueLogGCRunCompleted)
 	}
 }
-		}
-	}()
-}