From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7D854C2BA19 for ; Wed, 15 Apr 2020 19:13:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 573A920771 for ; Wed, 15 Apr 2020 19:13:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586978008; bh=+77x5whDjRYIYIEKhtra1cHGuZpcH2tP4qOEZzeVFjk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=XggI0etytC357QuY6/3udh6VyH7VkaZHPR4M5m2Ap6HfmF8EDK94LLSJzkwibnD0S 14QOfBKePfpxPeSLY1PONXRnpHV9U92f4pJvn5woIfQITx9Zlvv7sRavQp0rN0vUE1 AE4Aa8eMlpwBpaUEgbmx7Ui88qmLHQvFU1ioaGFE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437595AbgDOTNY (ORCPT ); Wed, 15 Apr 2020 15:13:24 -0400 Received: from mail.kernel.org ([198.145.29.99]:45914 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1416866AbgDOStu (ORCPT ); Wed, 15 Apr 2020 14:49:50 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8DDAE216FD; Wed, 15 Apr 2020 18:49:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586976589; bh=+77x5whDjRYIYIEKhtra1cHGuZpcH2tP4qOEZzeVFjk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=x3TNoJls4hPhoOA4VxCdJLgSEqj8lkqqE9plTnfW0oxubJrkZBcZC5Dx8+QLa59Zm LzpD/qAWSQCOMjBgmJHwaUiqekedwXymBtBui2/SO45AM/RYoos31z6ji09wNjADOR hTqbxoYfFdym3SDvSzR0PX0BCyLpa9sITAuGQY/U= From: paulmck@kernel.org To: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org Cc: stern@rowland.harvard.edu, parri.andrea@gmail.com, will@kernel.org, peterz@infradead.org, boqun.feng@gmail.com, npiggin@gmail.com, dhowells@redhat.com, j.alglave@ucl.ac.uk, luc.maranget@inria.fr, akiyks@gmail.com, "Paul E . McKenney" Subject: [PATCH lkmm tip/core/rcu 10/10] Documentation/litmus-tests/atomic: Add a test for smp_mb__after_atomic() Date: Wed, 15 Apr 2020 11:49:45 -0700 Message-Id: <20200415184945.16487-10-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200415183343.GA12265@paulmck-ThinkPad-P72> References: <20200415183343.GA12265@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Boqun Feng 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. Acked-by: Alan Stern Acked-by: Andrea Parri Signed-off-by: Boqun Feng Reviewed-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- Documentation/atomic_t.txt | 10 +++---- ...b__after_atomic-is-stronger-than-acquire.litmus | 32 ++++++++++++++++++++++ Documentation/litmus-tests/atomic/README | 5 ++++ 3 files changed, 42 insertions(+), 5 deletions(-) create mode 100644 Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus diff --git a/Documentation/atomic_t.txt b/Documentation/atomic_t.txt index 67d1d99f..0f1fded 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++; diff --git a/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus b/Documentation/litmus-tests/atomic/Atomic-RMW+mb__after_atomic-is-stronger-than-acquire.litmus new file mode 100644 index 0000000..9a8e31a --- /dev/null +++ b/Documentation/litmus-tests/atomic/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/litmus-tests/atomic/README b/Documentation/litmus-tests/atomic/README index a1b7241..714cf93 100644 --- a/Documentation/litmus-tests/atomic/README +++ b/Documentation/litmus-tests/atomic/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. -- 2.9.5