8058209: Race in G1 card scanning could allow scanning of memory covered by PLABs Summary: Read _top before _gc_time_stamp in saved_mark_word() with LoadLoad order to ensure we get a consistent view Reviewed-by: brutisso, dcubed, dholmes, stefank

8064811: Use THREAD instead of CHECK_NULL in return statements Reviewed-by: coleenp, simonis, dholmes

8064786: Fix debug build after 8062808: Turn on the -Wreturn-type warning Reviewed-by: stefank, tschatzl

8062036: ConcurrentMarkThread::slt may be invoked before ConcurrentMarkThread::makeSurrogateLockerThread causing intermittent crashes Summary: Suppress gc_alot during VM init, improve error for SLT uninitialized. Reviewed-by: jmasa, brutisso, tschatzl