Add more logs for b/276660612.

Test: m
Bug: 276660612
Change-Id: Ia47dc03bf46a93fb9cf375b1889b0de3f7244559
diff --git a/runtime/gc/collector/concurrent_copying.cc b/runtime/gc/collector/concurrent_copying.cc
index 5118523..1f123aa 100644
--- a/runtime/gc/collector/concurrent_copying.cc
+++ b/runtime/gc/collector/concurrent_copying.cc
@@ -1899,7 +1899,10 @@
         << " cc->is_marking=" << is_marking_;
     CHECK(self == thread_running_gc_)
         << "Only GC-running thread should access the mark stack "
-        << "in the GC exclusive mark stack mode";
+        << "in the GC exclusive mark stack mode. "
+        << "ref=" << to_ref
+        << " self->gc_marking=" << self->GetIsGcMarking()
+        << " cc->is_marking=" << is_marking_;
     // Access the GC mark stack without a lock.
     if (UNLIKELY(gc_mark_stack_->IsFull())) {
       ExpandGcMarkStack();