tools/memory-model: Add an exception for limitations on _unless() family

According to Luc, atomic_add_unless() is directly provided by herd7,
therefore it can be used in litmus tests. So change the limitation
section in README to unlimit the use of atomic_add_unless().

Cc: Luc Maranget <luc.maranget@inria.fr>
Acked-by: Andrea Parri <parri.andrea@gmail.com>
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/tools/memory-model/README b/tools/memory-model/README
index fc07b52f202865cb6cc8965df7786e0289ca5ba7..b9c562e9298166db8d47a4b319a97145af6616ab 100644 (file)
--- a/tools/memory-model/README
+++ b/tools/memory-model/README
@@ -207,11 +207,15 @@ The Linux-kernel memory model (LKMM) has the following limitations:
                case as a store release.
 
        b.      The "unless" RMW operations are not currently modeled:
-               atomic_long_add_unless(), atomic_add_unless(),
-               atomic_inc_unless_negative(), and
-               atomic_dec_unless_positive().  These can be emulated
+               atomic_long_add_unless(), atomic_inc_unless_negative(),
+               and atomic_dec_unless_positive().  These can be emulated
                in litmus tests, for example, by using atomic_cmpxchg().
 
+               One exception of this limitation is atomic_add_unless(),
+               which is provided directly by herd7 (so no corresponding
+               definition in linux-kernel.def).  atomic_add_unless() is
+               modeled by herd7 therefore it can be used in litmus tests.
+
        c.      The call_rcu() function is not modeled.  It can be
                emulated in litmus tests by adding another process that
                invokes synchronize_rcu() and the body of the callback