fix: initialize new drwMutex for each attempt in 'for {' loop. (#14009)

It is possible that GetLock() call remembers a previously
failed releaseAll() when there are networking issues, now
this state can have potential side effects.

This PR tries to avoid this side affect by making sure
to initialize NewNSLock() for each GetLock() attempts
made to avoid any prior state in the memory that can
interfere with the new lock grants.

cmd/data-scanner.go

@@ -72,14 +72,16 @@ var (
 // initDataScanner will start the scanner in the background.
 func initDataScanner(ctx context.Context, objAPI ObjectLayer) {
 	go func() {
+		r := rand.New(rand.NewSource(time.Now().UnixNano()))
 		// Run the data scanner in a loop
 		for {
-			select {
-			case <-ctx.Done():
-				return
-			default:
-				runDataScanner(ctx, objAPI)
+			runDataScanner(ctx, objAPI)
+			duration := time.Duration(r.Float64() * float64(scannerCycle.Get()))
+			if duration < time.Second {
+				// Make sure to sleep atleast a second to avoid high CPU ticks.
+				duration = time.Second
 			}
+			time.Sleep(duration)
 		}
 	}()
 }
@@ -106,20 +108,14 @@ func (s *safeDuration) Get() time.Duration {
 // There should only ever be one scanner running per cluster.
 func runDataScanner(pctx context.Context, objAPI ObjectLayer) {
 	// Make sure only 1 scanner is running on the cluster.
-	locker := objAPI.NewNSLock(minioMetaBucket, "runDataScanner.lock")
-	var ctx context.Context
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
-	for {
-		lkctx, err := locker.GetLock(pctx, dataScannerLeaderLockTimeout)
-		if err != nil {
-			time.Sleep(time.Duration(r.Float64() * float64(scannerCycle.Get())))
-			continue
-		}
-		ctx = lkctx.Context()
-		defer lkctx.Cancel()
-		break
-		// No unlock for "leader" lock.
+	locker := objAPI.NewNSLock(minioMetaBucket, "scanner/runDataScanner.lock")
+	lkctx, err := locker.GetLock(pctx, dataScannerLeaderLockTimeout)
+	if err != nil {
+		return
 	}
+	ctx := lkctx.Context()
+	defer lkctx.Cancel()
+	// No unlock for "leader" lock.
 
 	// Load current bloom cycle
 	nextBloomCycle := intDataUpdateTracker.current() + 1