Better comment and no accidental assignment

src/hotspot/share/logging/logAsyncWriter.cpp

@@ -42,7 +42,7 @@ class AsyncLogWriter::AsyncLogLocker : public StackObj {
   }
 
   ~AsyncLogLocker() {
-    assert(_holder = Thread::current_or_null(), "must be");
+    assert(_holder == Thread::current_or_null(), "must be");
     _holder = nullptr;
     _instance->_lock.unlock();
   }
@@ -92,17 +92,18 @@ void AsyncLogWriter::enqueue_locked(LogFileStreamOutput* output, const LogDecora
   _lock.notify();
 }
 
-// Check for degenerate cases of logging.
+// This function checks for cases where continuing with asynchronous logging may lead to stability issues, such as a deadlock.
 // If this returns true then we give up on logging asynchronously and do so synchronously instead.
 bool AsyncLogWriter::resort_to_synchronous_logging() {
   AsyncLogWriter* alw = AsyncLogWriter::instance();
   Thread* holding_thread = AsyncLogWriter::AsyncLogLocker::current_holder();
   Thread* this_thread = Thread::current_or_null();
   bool is_async_log_thread = this_thread != nullptr && alw == this_thread;
   bool is_recursively_logging = this_thread != nullptr && holding_thread == this_thread;
-  return    is_async_log_thread    // The async log producer is attempting to log, leading to recursive logging.
-         || is_recursively_logging // A thread enqueuing a message has attempted to log something.
-         || alw == nullptr;        // There is no AsyncLogWriter instance yet.
+  return is_async_log_thread    ||  // The async log producer is attempting to log, leading to recursive logging.
+         is_recursively_logging ||  // A thread enqueuing a message has attempted to log something.
+         alw == nullptr         ||  // There is no AsyncLogWriter instance yet.
+         this_thread == nullptr;    // The current thread is unattached.
 }
 
 bool AsyncLogWriter::enqueue(LogFileStreamOutput& output, const LogDecorations& decorations, const char* msg) {