From mboxrd@z Thu Jan 1 00:00:00 1970 From: paulmck@kernel.org Subject: [PATCH lkmm tip/core/rcu 05/10] Documentation: LKMM: Add litmus test for RCU GP guarantee where reader stores Date: Wed, 15 Apr 2020 11:49:40 -0700 Message-ID: <20200415184945.16487-5-paulmck@kernel.org> References: <20200415183343.GA12265@paulmck-ThinkPad-P72> Return-path: Received: from mail.kernel.org ([198.145.29.99]:45942 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1416861AbgDOSts (ORCPT ); Wed, 15 Apr 2020 14:49:48 -0400 In-Reply-To: <20200415183343.GA12265@paulmck-ThinkPad-P72> Sender: linux-arch-owner@vger.kernel.org List-ID: 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" 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 --- Documentation/litmus-tests/README | 5 +++ .../litmus-tests/rcu/RCU+sync+read.litmus | 37 ++++++++++++++++++++++ 2 files changed, 42 insertions(+) create mode 100644 Documentation/litmus-tests/rcu/RCU+sync+read.litmus diff --git a/Documentation/litmus-tests/README b/Documentation/litmus-tests/README index 84208bc..79d187f 100644 --- a/Documentation/litmus-tests/README +++ b/Documentation/litmus-tests/README @@ -7,3 +7,8 @@ RCU (/rcu directory) MP+onceassign+derefonce.litmus Demonstrates that rcu_assign_pointer() and rcu_dereference() to ensure that an RCU reader will not see pre-initialization garbage. + +RCU+sync+read.litmus +RCU+sync+free.litmus + Both the above litmus tests demonstrate the RCU grace period guarantee + that an RCU read-side critical section can never span a grace period. diff --git a/Documentation/litmus-tests/rcu/RCU+sync+read.litmus b/Documentation/litmus-tests/rcu/RCU+sync+read.litmus new file mode 100644 index 0000000..f341767 --- /dev/null +++ b/Documentation/litmus-tests/rcu/RCU+sync+read.litmus @@ -0,0 +1,37 @@ +C RCU+sync+read + +(* + * Result: Never + * + * This litmus test demonstrates that after a grace period, an RCU updater always + * sees all stores done in prior RCU read-side critical sections. Such + * read-side critical sections would have ended before the grace period ended. + * + * 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 = 0; +int y = 0; +} + +P0(int *x, int *y) +{ + rcu_read_lock(); + WRITE_ONCE(*x, 1); + WRITE_ONCE(*y, 1); + rcu_read_unlock(); +} + +P1(int *x, int *y) +{ + int r0; + int r1; + + r0 = READ_ONCE(*x); + synchronize_rcu(); + r1 = READ_ONCE(*y); +} + +exists (1:r0=1 /\ 1:r1=0) -- 2.9.5