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 [thread overview]
Message-ID: <20200227004049.6853-6-boqun.feng@gmail.com> (raw)
In-Reply-To: <20200227004049.6853-1-boqun.feng@gmail.com>
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
next prev parent reply other threads:[~2020-02-27 0:41 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 0:40 [PATCH v3 0/5] Documentation/locking/atomic: Add litmus tests for atomic APIs Boqun Feng
2020-02-27 0:40 ` [PATCH v3 1/5] tools/memory-model: Add an exception for limitations on _unless() family Boqun Feng
2020-02-27 16:32 ` Alan Stern
2020-02-27 16:49 ` Luc Maranget
2020-02-27 18:16 ` Alan Stern
2020-02-27 17:52 ` Andrea Parri
2020-02-27 0:40 ` [PATCH v3 2/5] Documentation/locking/atomic: Fix atomic-set litmus test Boqun Feng
2020-02-27 16:34 ` Alan Stern
2020-02-28 6:30 ` Boqun Feng
2020-02-27 0:40 ` [PATCH v3 3/5] Documentation/locking/atomic: Introduce atomic-tests directory Boqun Feng
2020-02-27 16:36 ` Alan Stern
2020-02-27 0:40 ` [PATCH v3 4/5] Documentation/locking/atomic: Add a litmus test for atomic_set() Boqun Feng
2020-02-27 16:37 ` Alan Stern
2020-02-27 17:43 ` Andrea Parri
2020-02-27 0:40 ` Boqun Feng [this message]
2020-02-27 16:38 ` [PATCH v3 5/5] Documentation/locking/atomic: Add a litmus test smp_mb__after_atomic() Alan Stern
2020-02-27 15:47 ` [PATCH v3 0/5] Documentation/locking/atomic: Add litmus tests for atomic APIs Paul E. McKenney
2020-02-27 17:54 ` Andrea Parri
2020-02-28 6:12 ` Boqun Feng
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