--- a/src/hotspot/share/gc/g1/vm_operations_g1.cpp	Sat Jan 13 02:56:22 2018 +0100
+++ b/src/hotspot/share/gc/g1/vm_operations_g1.cpp	Wed Jan 17 19:05:58 2018 +0100
@@ -139,13 +139,17 @@
       // An allocation had been requested. Do it, eventually trying a stronger
       // kind of GC.
       _result = g1h->satisfy_failed_allocation(_word_size, _allocation_context, &_pause_succeeded);
-    } else if (!g1h->has_regions_left_for_allocation()) {
-      // There has been a request to perform a GC to free some space. We have no
-      // information on how much memory has been asked for. In case there are
-      // absolutely no regions left to allocate into, do a maximally compacting full GC.
-      log_info(gc, ergo)("Attempting maximally compacting collection");
-      _pause_succeeded = g1h->do_full_collection(false, /* explicit gc */
-                                                 true   /* clear_all_soft_refs */);
+    } else {
+      bool should_upgrade_to_full = !g1h->should_do_concurrent_full_gc(_gc_cause) &&
+                                    !g1h->has_regions_left_for_allocation();
+      if (should_upgrade_to_full) {
+        // There has been a request to perform a GC to free some space. We have no
+        // information on how much memory has been asked for. In case there are
+        // absolutely no regions left to allocate into, do a maximally compacting full GC.
+        log_info(gc, ergo)("Attempting maximally compacting collection");
+        _pause_succeeded = g1h->do_full_collection(false, /* explicit gc */
+                                                   true   /* clear_all_soft_refs */);
+      }
     }
     guarantee(_pause_succeeded, "Elevated collections during the safepoint must always succeed.");
   } else {

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/test/hotspot/jtreg/gc/g1/TestConcurrentSystemGC.java	Wed Jan 17 19:05:58 2018 +0100
@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2018, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test TestConcurrentSystemGC
+ * @bug 8195158
+ * @summary Test that a System.gc() with -XX:+ExplicitGCInvokesConcurrent
+ *          is *not* upgraded to STW full GC
+ * @key gc
+ * @requires vm.gc.G1
+ * @library /test/lib
+ * @modules java.base/jdk.internal.misc
+ *          java.management
+ * @run main/othervm -XX:+UseG1GC -XX:+ExplicitGCInvokesConcurrent -Xmx8m -Xms8m -XX:G1HeapRegionSize=1m TestConcurrentSystemGC
+ */
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class TestConcurrentSystemGC {
+    public static List<char[]> memory;
+    public static void main(String[] args) throws Exception {
+        memory = new ArrayList<>();
+        try {
+            while (true) {
+                memory.add(new char[1024 * 128]);
+                System.gc(); // should not trigger any assertions
+            }
+        } catch (OutOfMemoryError e) {
+            memory = null;
+            System.gc();
+        }
+    }
+}