8254877: GCLogPrecious::_lock rank constrains what locks you are allo…

…wed to have when crashing

Reviewed-by: eosterlund

src/hotspot/share/gc/shared/gcLogPrecious.cpp

@@ -33,7 +33,7 @@ Mutex* GCLogPrecious::_lock = NULL;
 void GCLogPrecious::initialize() {
   _lines = new (ResourceObj::C_HEAP, mtGC) stringStream();
   _temp = new (ResourceObj::C_HEAP, mtGC) stringStream();
-  _lock = new Mutex(Mutex::tty,
+  _lock = new Mutex(Mutex::event, /* The lowest lock rank I could find */
                     "GCLogPrecious Lock",
                     true,
                     Mutex::_safepoint_check_never);
@@ -77,11 +77,23 @@ void GCLogPrecious::vwrite_and_debug(LogTargetHandle log,
 }
 
 void GCLogPrecious::print_on_error(outputStream* st) {
-  if (_lines != NULL) {
-    MutexLocker locker(_lock, Mutex::_no_safepoint_check_flag);
-    if (_lines->size() > 0) {
-      st->print_cr("GC Precious Log:");
-      st->print_cr("%s", _lines->base());
-    }
+  st->print_cr("GC Precious Log:");
+
+  if (_lines == NULL) {
+    st->print_cr("<Not initialized>\n");
+    return;
+  }
+
+  if (!_lock->try_lock_without_rank_check()) {
+    st->print_cr("<Skipped>\n");
+    return;
   }
+
+  if (_lines->size() == 0) {
+    st->print_cr("<Empty>\n");
+  } else {
+    st->print_cr("%s", _lines->base());
+  }
+
+  _lock->unlock();
 }