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From:   Boqun Feng <boqun.feng@gmail.com>
To:     linux-kernel@vger.kernel.org
Cc:     Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Boqun Feng <boqun.feng@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Akira Yokosawa <akiyks@gmail.com>,
        Daniel Lustig <dlustig@nvidia.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linux-arch@vger.kernel.org, linux-doc@vger.kernel.org
Subject: [PATCH v3 5/5] Documentation/locking/atomic: Add a litmus test smp_mb__after_atomic()
Date:   Thu, 27 Feb 2020 08:40:49 +0800
Message-Id: <20200227004049.6853-6-boqun.feng@gmail.com>
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We already use a litmus test in atomic_t.txt to describe atomic RMW +
smp_mb__after_atomic() is stronger than acquire (both the read and the
write parts are ordered). So make it a litmus test in atomic-tests
directory, so that people can access the litmus easily.

Additionally, change the processor numbers "P1, P2" to "P0, P1" in
atomic_t.txt for the consistency with the processor numbers in the
litmus test, which herd can handle.

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
---
 ...ter_atomic-is-stronger-than-acquire.litmus | 32 +++++++++++++++++++
 Documentation/atomic-tests/README             |  5 +++
 Documentation/atomic_t.txt                    | 10 +++---
 3 files changed, 42 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/atomic-tests/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus

diff --git a/Documentation/atomic-tests/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus b/Documentation/atomic-tests/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
new file mode 100644
index 000000000000..9a8e31a44b28
--- /dev/null
+++ b/Documentation/atomic-tests/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus
@@ -0,0 +1,32 @@
+C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+
+(*
+ * Result: Never
+ *
+ * Test that an atomic RMW followed by a smp_mb__after_atomic() is
+ * stronger than a normal acquire: both the read and write parts of
+ * the RMW are ordered before the subsequential memory accesses.
+ *)
+
+{
+}
+
+P0(int *x, atomic_t *y)
+{
+	int r0;
+	int r1;
+
+	r0 = READ_ONCE(*x);
+	smp_rmb();
+	r1 = atomic_read(y);
+}
+
+P1(int *x, atomic_t *y)
+{
+	atomic_inc(y);
+	smp_mb__after_atomic();
+	WRITE_ONCE(*x, 1);
+}
+
+exists
+(0:r0=1 /\ 0:r1=0)
diff --git a/Documentation/atomic-tests/README b/Documentation/atomic-tests/README
index a1b72410b539..714cf93816ea 100644
--- a/Documentation/atomic-tests/README
+++ b/Documentation/atomic-tests/README
@@ -7,5 +7,10 @@ tools/memory-model/README.
 LITMUS TESTS
 ============
 
+Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
+	Test that an atomic RMW followed by a smp_mb__after_atomic() is
+	stronger than a normal acquire: both the read and write parts of
+	the RMW are ordered before the subsequential memory accesses.
+
 Atomic-RMW-ops-are-atomic-WRT-atomic_set.litmus
 	Test that atomic_set() cannot break the atomicity of atomic RMWs.
diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt
index 67d1d99f8589..0f1fdedf36bb 100644
--- a/Documentation/atomic_t.txt
+++ b/Documentation/atomic_t.txt
@@ -233,19 +233,19 @@ as well. Similarly, something like:
 is an ACQUIRE pattern (though very much not typical), but again the barrier is
 strictly stronger than ACQUIRE. As illustrated:
 
-  C strong-acquire
+  C Atomic-RMW+mb__after_atomic-is-stronger-than-acquire
 
   {
   }
 
-  P1(int *x, atomic_t *y)
+  P0(int *x, atomic_t *y)
   {
     r0 = READ_ONCE(*x);
     smp_rmb();
     r1 = atomic_read(y);
   }
 
-  P2(int *x, atomic_t *y)
+  P1(int *x, atomic_t *y)
   {
     atomic_inc(y);
     smp_mb__after_atomic();
@@ -253,14 +253,14 @@ strictly stronger than ACQUIRE. As illustrated:
   }
 
   exists
-  (r0=1 /\ r1=0)
+  (0:r0=1 /\ 0:r1=0)
 
 This should not happen; but a hypothetical atomic_inc_acquire() --
 (void)atomic_fetch_inc_acquire() for instance -- would allow the outcome,
 because it would not order the W part of the RMW against the following
 WRITE_ONCE.  Thus:
 
-  P1			P2
+  P0			P1
 
 			t = LL.acq *y (0)
 			t++;
-- 
2.25.0