Gregory, I guess we should have just read Documentation/memory-barriers.text Here's the snippet: Any atomic operation that modifies some state in memory and returns information about the state (old or new) implies an SMP-conditional general memory barrier (smp_mb()) on each side of the actual operation (with the exception of explicit lock operations, described later). These include: xchg(); cmpxchg(); atomic_cmpxchg(); atomic_inc_return(); atomic_dec_return(); atomic_add_return(); atomic_sub_return(); atomic_inc_and_test(); atomic_dec_and_test(); atomic_sub_and_test(); atomic_add_negative(); atomic_add_unless(); test_and_set_bit(); test_and_clear_bit(); test_and_change_bit(); -- Steve - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html