[PATCH URCU formal] Remove spurious read-side infinite loops.

Paul E. McKenney
2009-02-20T01:57:07Z

Remove spurious read-side infinite loops from urcu_reader() model.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
formal-model/urcu.spin | 21 +++++++++++++++++----
1 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/formal-model/urcu.spin b/formal-model/urcu.spin
index 611464b..eea18e8 100644
--- a/formal-model/urcu.spin
+++ b/formal-model/urcu.spin
@@ -27,6 +27,10 @@ bit free = 0; /* Has RCU reclamation happened, e.g., kfree()? */
bit need_mb = 0; /* =1 says need reader mb, =0 for reader response. */
byte reader_progress[4];
/* Count of read-side statement executions. */
+bit reader_done = 0;
+ /* =0 says reader still running, =1 says done. */
+bit updater_done = 0;
+ /* =0 says updater still running, =1 says done. */

/* urcu definitions and variables, taken straight from the algorithm. */

@@ -50,7 +54,7 @@ proctype urcu_reader()
do
:: need_mb == 1 ->
need_mb = 0;
- :: 1 -> skip;
+ :: !updater_done -> skip;
:: 1 -> break;
od;

@@ -92,7 +96,7 @@ proctype urcu_reader()
reader_progress[2] +
reader_progress[3] == 0) && need_mb == 1 ->
need_mb = 0;
- :: 1 -> skip;
+ :: !updater_done -> skip;
:: 1 -> break;
od;
urcu_active_readers = tmp;
@@ -150,7 +154,7 @@ proctype urcu_reader()
do
:: need_mb == 1 ->
need_mb = 0;
- :: 1 -> skip;
+ :: !updater_done -> skip;
:: 1 -> break;
od;
:: else -> skip;
@@ -167,11 +171,14 @@ proctype urcu_reader()
od;
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;
- :: 1 -> skip;
+ :: !updater_done -> skip;
:: 1 -> break;
od;
}
@@ -248,6 +255,12 @@ proctype urcu_updater()

/* free-up step, e.g., kfree(). */
free = 1;
+
+ /*
+ * Signal updater done, ending any otherwise-infinite loops
+ * in the reading process.
+ */
+ updater_done = 1;
}

/*
--
1.5.2.5