Exclude free-free accesses from racing

src/domains/access.ml

@@ -362,16 +362,14 @@ struct
 end
 
 
-(* Check if two accesses may race and if yes with which confidence *)
+(** Check if two accesses may race. *)
 let may_race A.{kind; acc; _} A.{kind=kind2; acc=acc2; _} =
-  if kind = Read && kind2 = Read then
-    false (* two read/read accesses do not race *)
-  else if not (get_bool "ana.race.free") && (kind = Free || kind2 = Free) then
-    false
-  else if not (MCPAccess.A.may_race acc acc2) then
-    false (* analysis-specific information excludes race *)
-  else
-    true
+  match kind, kind2 with
+  | Read, Read -> false (* two read/read accesses do not race *)
+  | Free, Free -> false (* two free/free accesses do not race *)
+  | Free, _
+  | _, Free when not (get_bool "ana.race.free") -> false
+  | _, _ -> MCPAccess.A.may_race acc acc2 (* analysis-specific information excludes race *)
 
 (** Access sets for race detection and warnings. *)
 module WarnAccs =

src/util/options.schema.json

@@ -998,7 +998,7 @@
           "properties": {
             "free": {
               "title": "ana.race.free",
-              "description": "Consider memory free as racing write.",
+              "description": "Consider memory free as racing with read or write (but not another free).",
               "type": "boolean",
               "default": true
             },

tests/regression/04-mutex/64-free_direct_rc.c

@@ -8,11 +8,23 @@ void *t_fun(void *arg) {
   return NULL;
 }
 
+void *t_fun2(void *arg) {
+  int *p = (int *) arg;
+  free(p); // NORACE
+  return NULL;
+}
+
 int main(void) {
   pthread_t id;
-  int *p = malloc(sizeof(int));
+  int *p;
+  p = malloc(sizeof(int));
   pthread_create(&id, NULL, t_fun, (void *) p);
   free(p); // RACE!
   pthread_join (id, NULL);
+
+  p = malloc(sizeof(int));
+  pthread_create(&id, NULL, t_fun2, (void *) p);
+  free(p); // NORACE
+  pthread_join (id, NULL);
   return 0;
 }