linux-kernel - [PATCH lkmm tip/core/rcu 07/10] tools/memory-model: Add an exception for limitations on

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Date:   Wed, 15 Apr 2020 11:49:42 -0700
From:   paulmck@...nel.org
To:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org
Cc:     stern@...land.harvard.edu, parri.andrea@...il.com, will@...nel.org,
        peterz@...radead.org, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH lkmm tip/core/rcu 07/10] tools/memory-model: Add an exception for limitations on _unless() family

From: Boqun Feng <boqun.feng@...il.com>

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@...ia.fr>
Acked-by: Andrea Parri <parri.andrea@...il.com>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Boqun Feng <boqun.feng@...il.com>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/memory-model/README | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/tools/memory-model/README b/tools/memory-model/README
index fc07b52..b9c562e 100644
--- 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
-- 
2.9.5