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,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 DA5E2C2BA19 for ; Wed, 15 Apr 2020 19:11:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B2EF520768 for ; Wed, 15 Apr 2020 19:11:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586977897; bh=Iqy7olmWTGFsAB7j1jAOyQi0betLtkAJ66NGYId1SDc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=qZiz5G/txJ00GadAajgutYgcC5uQC8tExEnX92Acfe7jIo8NE3UwUBBktjs0ME9rg DX+8szLG0Xi3ltWXpQ6cmAfGwoM/wfx7fXUHAQvxmroiKMKM2G0XM+fLC/fiMwuVZJ GDTJI/cQHzAhoHrrwpfVL5ZjCAHL47SHr3k1DoYE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504532AbgDOTLd (ORCPT ); Wed, 15 Apr 2020 15:11:33 -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 S1416860AbgDOSts (ORCPT ); Wed, 15 Apr 2020 14:49:48 -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 C2B3321569; Wed, 15 Apr 2020 18:49:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586976588; bh=Iqy7olmWTGFsAB7j1jAOyQi0betLtkAJ66NGYId1SDc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QwQ6eDPRXqiq474j0FH2lAMcFRsLU7qsbtLZtPR0KiLFnFvvJ9Ezn9n+yQC7WWI0J +/ItFIGgTsEoagfUmqmYgv+b7Ci9aJ8Bs5uCtvlHcuigaQeHZzM87yj7gutF3Tr+4I rQa2RjPhLz17mW/eZrcP9mX3xiYEIoovlJKc4K4s= 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, "Joel Fernandes (Google)" , "Paul E . McKenney" Subject: [PATCH lkmm tip/core/rcu 04/10] Documentation: LKMM: Add litmus test for RCU GP guarantee where updater frees object Date: Wed, 15 Apr 2020 11:49:39 -0700 Message-Id: <20200415184945.16487-4-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: "Joel Fernandes (Google)" This adds an example for the important RCU grace period guarantee, which shows an RCU reader can never span a grace period. Acked-by: Andrea Parri Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- .../litmus-tests/rcu/RCU+sync+free.litmus | 42 ++++++++++++++++++++++ 1 file changed, 42 insertions(+) create mode 100644 Documentation/litmus-tests/rcu/RCU+sync+free.litmus diff --git a/Documentation/litmus-tests/rcu/RCU+sync+free.litmus b/Documentation/litmus-tests/rcu/RCU+sync+free.litmus new file mode 100644 index 0000000..4ee67e1 --- /dev/null +++ b/Documentation/litmus-tests/rcu/RCU+sync+free.litmus @@ -0,0 +1,42 @@ +C RCU+sync+free + +(* + * Result: Never + * + * This litmus test demonstrates that an RCU reader can never see a write that + * follows a grace period, if it did not see writes that precede that grace + * period. + * + * This is a typical pattern of RCU usage, where the write before the grace + * period assigns a pointer, and the writes following the grace period destroy + * the object that the pointer used to point to. + * + * This is one implication of the RCU grace-period guarantee, which says (among + * other things) that an RCU read-side critical section cannot span a grace period. + *) + +{ +int x = 1; +int *y = &x; +int z = 1; +} + +P0(int *x, int *z, int **y) +{ + int *r0; + int r1; + + rcu_read_lock(); + r0 = rcu_dereference(*y); + r1 = READ_ONCE(*r0); + rcu_read_unlock(); +} + +P1(int *x, int *z, int **y) +{ + rcu_assign_pointer(*y, z); + synchronize_rcu(); + WRITE_ONCE(*x, 0); +} + +exists (0:r0=x /\ 0:r1=0) -- 2.9.5