[PATCH URCU formal] Add liveness checks to user-level RCU model.

From: Paul E. McKenney
Date: Fri Feb 20 2009 - 12:39:55 EST

Break all potentially infinite loops in both urcu_reader() and
urcu_updater(), ensure that urcu_reader() will process any memory barriers
that urcu_updater() might issue, and formulate a "never" claim that checks
to make sure that if either urcu_reader() or urcu_updater() completes,
then the other will eventually also complete. Since urcu_reader()
now has a finite number of steps, it must eventually complete.

Also replace the code at the end of urcu_reader() that previously absorbed
late memory-barrier requests from urcu_updater with code in urcu_writer()
that checks to see if urcu_reader() has completed.

Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
---
formal-model/urcu.sh | 26 ++++++++++-
formal-model/urcu.spin | 113 ++++++++++++++++++++++-------------------------
2 files changed, 77 insertions(+), 62 deletions(-)

diff --git a/formal-model/urcu.sh b/formal-model/urcu.sh
index b76c764..5e525ec 100644
--- a/formal-model/urcu.sh
+++ b/formal-model/urcu.sh
@@ -1,3 +1,25 @@
+#!/bin/sh
+#
+# Compiles and runs the urcu.spin Promela model.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+#
+# Copyright (C) IBM Corporation, 2009
+#
+# Authors: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
+
spin -a urcu.spin
-cc -DSAFETY -o pan pan.c
-./pan
+cc -o pan pan.c
+./pan -a
diff --git a/formal-model/urcu.spin b/formal-model/urcu.spin
index 3e18457..cf1f670 100644
--- a/formal-model/urcu.spin
+++ b/formal-model/urcu.spin
@@ -40,21 +40,28 @@ bit updater_done = 0;
byte urcu_gp_ctr = 1;
byte urcu_active_readers = 0;

+/* must be at least the number of smp_mb() statements in urcu_updater(). */
+#define N_SMP_MB 9
+
/* Model the RCU read-side critical section. */

proctype urcu_reader()
{
bit done = 0;
+ byte i;
bit mbok;
byte tmp;
byte tmp_removed;
byte tmp_free;

/* Absorb any early requests for memory barriers. */
+ i = 0;
do
- :: need_mb == 1 ->
+ :: i < N_SMP_MB && need_mb == 1 ->
need_mb = 0;
- :: !updater_done -> skip;
+ i++;
+ :: i < N_SMP_MB ->
+ i++;
:: 1 -> break;
od;

@@ -91,12 +98,17 @@ proctype urcu_reader()
if
:: (tmp & RCU_GP_CTR_NEST_MASK) == 0 ->
tmp = urcu_gp_ctr;
+ i = 0;
do
- :: (reader_progress[1] +
+ :: i < N_SMP_MB &&
+ (reader_progress[1] +
reader_progress[2] +
- reader_progress[3] == 0) && need_mb == 1 ->
+ reader_progress[3] == 0) &&
+ need_mb == 1 ->
need_mb = 0;
- :: !updater_done -> skip;
+ i++;
+ :: i < N_SMP_MB ->
+ i++;
:: 1 -> break;
od;
urcu_active_readers = tmp;
@@ -151,10 +163,13 @@ proctype urcu_reader()
if
:: mbok == 1 ->
/* We get here if mb processing is safe. */
+ i = 0;
do
- :: need_mb == 1 ->
+ :: i < N_SMP_MB && need_mb == 1 ->
need_mb = 0;
- :: !updater_done -> skip;
+ i++;
+ :: i < N_SMP_MB ->
+ i++;
:: 1 -> break;
od;
:: else -> skip;
@@ -169,36 +184,30 @@ proctype urcu_reader()
:: else -> skip;
fi
od;
+
+ /* Make sure any concurrent grace period was sufficiently long. */
assert((tmp_free == 0) || (tmp_removed == 1));

/* Reader has completed. */
reader_done = 1;
-
- /* Process any late-arriving memory-barrier requests. */
- do
- :: need_mb == 1 ->
- need_mb = 0;
- :: !updater_done -> skip;
- :: 1 -> break;
- od;
}

+#define smp_mb() \
+ need_mb = 1; \
+ do \
+ :: !reader_done && need_mb == 1 -> skip; \
+ :: reader_done -> break; \
+ :: need_mb == 0 -> break; \
+ od
+
/* Model the RCU update process. */

proctype urcu_updater()
{
/* prior synchronize_rcu(), second counter flip. */
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
do
:: 1 ->
if
@@ -209,27 +218,15 @@ proctype urcu_updater()
:: else -> break;
fi;
od;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();

/* Removal statement, e.g., list_del_rcu(). */
removed = 1;

/* current synchronize_rcu(), first counter flip. */
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
do
:: 1 ->
if
@@ -240,24 +237,12 @@ proctype urcu_updater()
:: else -> break;
fi;
od;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();

/* current synchronize_rcu(), second counter flip. */
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
urcu_gp_ctr = urcu_gp_ctr + RCU_GP_CTR_BIT;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();
do
:: 1 ->
if
@@ -268,11 +253,7 @@ proctype urcu_updater()
:: else -> break;
fi;
od;
- need_mb = 1;
- do
- :: need_mb == 1 -> skip;
- :: need_mb == 0 -> break;
- od;
+ smp_mb();

/* free-up step, e.g., kfree(). */
free = 1;
@@ -299,3 +280,15 @@ init {
run urcu_updater();
}
}
+
+/* Require that both reader and updater eventually get done. */
+
+never {
+ do
+ :: skip;
+ :: reader_done != 0 || updater_done != 0 -> break;
+ od;
+accept: do
+ :: reader_done == 0 || updater_done == 0;
+ od;
+}
--
1.5.2.5

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