coccinelle: double_lock: improve performance when no double lock exists

The 'balanced' rule collects the locks that are taken and released
under the same condition, to prevent them from being reported as a
double lock. It runs on every file that contains a lock call.

To avoid this, collect the double-lock candidates first, so that
'balanced' runs only when one exists. The report then excludes what
'balanced' found.

Every double lock that can be reported is also a candidate, so the
same reports are made as before and the output does not change. A
report-mode run over every .c file in the tree produces identical
output.

Signed-off-by: Sang-Heon Jeon <ekffu200098@gmail.com>
Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>

scripts/coccinelle/locks/double_lock.cocci

@@ -38,7 +38,20 @@ write_lock@p1
 write_trylock@p1
 ) (E1@p,...);
 
-@balanced@
+@r_candidate exists@
+expression x <= locked.E1;
+expression locked.E1;
+expression E2;
+identifier lock;
+position locked.p,p1,p2;
+@@
+
+lock@p1 (E1@p,...);
+... when != E1
+    when != \(x = E2\|&x\)
+lock@p2 (E1,...);
+
+@balanced depends on r_candidate@
 position p1 != locked.p1;
 position locked.p;
 identifier lock,unlock;