Running: JDK8-b86/bin/java -XX:+UseConcMarkSweepGC -XX:-UseCMSCompactAtFullCollection SystemGC

public class SystemGC {
  public static void main(String [] args) {
    while (true) {
      System.gc();
    }
  }
}

triggers this assert:
# Internal Error (/HUDSON/workspace/2-build-linux-amd64/jdk8/4052/hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp:931), pid=15212, tid=140225625880320
# assert(used() == used_after_gc && used_after_gc <= capacity()) failed: used: 0 used_after_gc: 292080 capacity: 1431699456

This assert was introduced with this change:
changeset: 4450:8617e38bb4cb
user: jmasa
date: Mon Feb 11 10:31:56 2013 -0800
summary: 8008508: CMS does not correctly reduce heap size after a Full GC