[#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

@@ -21,20 +21,25 @@ func (c *cache) runGCLoop(ctx context.Context) {
 			case <-ctx.Done():
 				return
 			case <-t.C:
-				// This serves to synchronize the c.db field when changing mode as well.
-				c.modeMtx.RLock()
-				ro := c.readOnly()
-				c.modeMtx.RUnlock()
-				if ro {
-					continue
-				}
-
-				// 0.5 is the recommended value so that write amplification of the value log is 2.
-				// See https://pkg.go.dev/github.com/dgraph-io/badger/v4#DB.RunValueLogGC for more info.
-				for c.db.RunValueLogGC(0.5) == nil {
-					c.log.Debug(logs.WritecacheDBValueLogGCRunCompleted)
-				}
+				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()
+	if ro {
+		return
+	}
+
+	// 0.5 is the recommended value so that write amplification of the value log is 2.
+	// See https://pkg.go.dev/github.com/dgraph-io/badger/v4#DB.RunValueLogGC for more info.
+	for c.db.RunValueLogGC(0.5) == nil {
+		c.log.Debug(logs.WritecacheDBValueLogGCRunCompleted)
+	}
+}