model: release_seq_head - rewrite RMW recursion as loop

A bug in release sequences coce (independent of this patch) causes a huge
blowup of the recursion, yielding strange stack errors. So I address "@todo
Might it be better to make this into a loop", causing a loop of memory usage
instead. This can be triggered, for example, with:

  ./run.sh ./test/linuxrwlocks.o -e 1 -f 4 -m 1

diff --git a/model.cc b/model.cc
index 8a8007097da391e039128cdd1c5a850c229d0f59..39cc82115495d35be8d52bb4a023daf6424fe9f1 100644 (file)
--- a/model.cc
+++ b/model.cc
@@ -1083,17 +1083,14 @@ bool ModelChecker::thin_air_constraint_may_allow(const ModelAction * writer, con
  */
 bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *release_heads) const
 {
-       if (!rf) {
-               /* read from future: need to settle this later */
-               return false; /* incomplete */
-       }
+       while (rf) {
+               ASSERT(rf->is_write());
 
-       ASSERT(rf->is_write());
+               if (rf->is_release())
+                       release_heads->push_back(rf);
+               if (!rf->is_rmw())
+                       break; /* End of RMW chain */
 
-       if (rf->is_release())
-               release_heads->push_back(rf);
-       if (rf->is_rmw()) {
-               /* We need a RMW action that is both an acquire and release to stop */
                /** @todo Need to be smarter here...  In the linux lock
                 * example, this will run to the beginning of the program for
                 * every acquire. */
@@ -1101,13 +1098,17 @@ bool ModelChecker::release_seq_head(const ModelAction *rf, rel_heads_list_t *rel
                 * thread has a release preceded by an acquire and you've seen
                 *       both. */
 
+               /* acq_rel RMW is a sufficient stopping condition */
                if (rf->is_acquire() && rf->is_release())
                        return true; /* complete */
 
-               /** @todo Might it be better to make this into a loop... */
-
-               return release_seq_head(rf->get_reads_from(), release_heads);
+               rf = rf->get_reads_from();
+       };
+       if (!rf) {
+               /* read from future: need to settle this later */
+               return false; /* incomplete */
        }
+
        if (rf->is_release())
                return true; /* complete */