use all the available nr_requests for NVMe (#18920)

cmd/mrf.go

@@ -47,7 +47,7 @@ type mrfState struct {
 	ctx   context.Context
 	pools *erasureServerPools
 
-	mu   sync.Mutex
+	mu   sync.RWMutex
 	opCh chan partialOperation
 }
 
@@ -72,6 +72,9 @@ func (m *mrfState) addPartialOp(op partialOperation) {
 		return
 	}
 
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
 	select {
 	case m.opCh <- op:
 	default: