8332506: SIGFPE In ObjectSynchronizer::is_async_deflation_needed()

src/hotspot/share/runtime/synchronizer.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1264,36 +1264,49 @@ static bool monitors_used_above_threshold(MonitorList* list) {
   if (MonitorUsedDeflationThreshold == 0) {  // disabled case is easy
     return false;
   }
-  // Start with ceiling based on a per-thread estimate:
-  size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
-  size_t old_ceiling = ceiling;
-  if (ceiling < list->max()) {
-    // The max used by the system has exceeded the ceiling so use that:
-    ceiling = list->max();
-  }
   size_t monitors_used = list->count();
   if (monitors_used == 0) {  // empty list is easy
     return false;
   }
-  if (NoAsyncDeflationProgressMax != 0 &&
-      _no_progress_cnt >= NoAsyncDeflationProgressMax) {
-    double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
-    size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
-    ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
-    log_info(monitorinflation)("Too many deflations without progress; "
-                               "bumping in_use_list_ceiling from " SIZE_FORMAT
-                               " to " SIZE_FORMAT, old_ceiling, new_ceiling);
-    _no_progress_cnt = 0;
-    ceiling = new_ceiling;
-  }
+  size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
+  // Make sure that we use a ceiling value that is not lower than
+  // previous, not lower than the recorded max used by the system, and
+  // not lower than the current number of monitors in use (which can
+  // race ahead of max). The result is guaranteed > 0.
+  size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
 
   // Check if our monitor usage is above the threshold:
   size_t monitor_usage = (monitors_used * 100LL) / ceiling;
   if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
+    // Deflate monitors if over the threshold percentage, unless no
+    // progress on previous deflations.
+    bool is_above_threshold = true;
+
+    // Check if it's time to adjust the in_use_list_ceiling up, due
+    // to too many async deflation attempts without any progress.
+    if (NoAsyncDeflationProgressMax != 0 &&
+        _no_progress_cnt >= NoAsyncDeflationProgressMax) {
+      double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
+      size_t delta = (size_t)(ceiling * remainder) + 1;
+      size_t new_ceiling = (ceiling > SIZE_MAX - delta)
+        ? SIZE_MAX         // Overflow, let's clamp new_ceiling.
+        : ceiling + delta;
+
+      ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
+      log_info(monitorinflation)("Too many deflations without progress; "
+                                 "bumping in_use_list_ceiling from " SIZE_FORMAT
+                                 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
+      _no_progress_cnt = 0;
+      ceiling = new_ceiling;
+
+      // Check if our monitor usage is still above the threshold:
+      monitor_usage = (monitors_used * 100LL) / ceiling;
+      is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
+    }
     log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
                                ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
                                monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
-    return true;
+    return is_above_threshold;
   }
 
   return false;