re PR libstdc++/54172 (__cxa_guard_acquire thread-safety issue)

	PR libstdc++/54172
	* libsupc++/guard.cc (__cxa_guard_acquire): Fix up the last
	argument of the first __atomic_compare_exchange_n.

From-SVN: r191190

libstdc++-v3/ChangeLog

+2012-09-11  Jakub Jelinek  <jakub@redhat.com>
+
+	PR libstdc++/54172
+	* libsupc++/guard.cc (__cxa_guard_acquire): Fix up the last
+	argument of the first __atomic_compare_exchange_n.
+
 2012-09-10  Sebastian Huber  <sebastian.huber@embedded-brains.de>
 	    Jonathan Wakely  <jwakely.gcc@gmail.com>
 

libstdc++-v3/libsupc++/guard.cc

@@ -253,7 +253,7 @@ namespace __cxxabiv1
 	    int expected(0);
 	    if (__atomic_compare_exchange_n(gi, &expected, pending_bit, false,
 					    __ATOMIC_ACQ_REL,
-					    __ATOMIC_RELAXED))
+					    __ATOMIC_ACQUIRE))
 	      {
 		// This thread should do the initialization.
 		return 1;