Coccinelle: Add locks/double_lock.cocci

Find double locks.  False positives may occur when some paths cannot
occur at execution, due to the values of variables, and when there is
an intervening function call that releases the lock.
Signed-off-by: Nicolas Palix <npalix@diku.dk>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Michal Marek <mmarek@suse.cz>

scripts/coccinelle/locks/double_lock.cocci

+/// Find double locks.  False positives may occur when some paths cannot
+/// occur at execution, due to the values of variables, and when there is
+/// an intervening function call that releases the lock.
+///
+// Confidence: Moderate
+// Copyright: (C) 2010 Nicolas Palix, DIKU.  GPLv2.
+// Copyright: (C) 2010 Julia Lawall, DIKU.  GPLv2.
+// Copyright: (C) 2010 Gilles Muller, INRIA/LiP6.  GPLv2.
+// URL: http://coccinelle.lip6.fr/
+// Comments:
+// Options: -no_includes -include_headers
+
+virtual org
+virtual report
+
+@locked@
+position p1;
+expression E1;
+position p;
+@@
+
+(
+mutex_lock@p1
+|
+mutex_trylock@p1
+|
+spin_lock@p1
+|
+spin_trylock@p1
+|
+read_lock@p1
+|
+read_trylock@p1
+|
+write_lock@p1
+|
+write_trylock@p1
+) (E1@p,...);
+
+@balanced@
+position p1 != locked.p1;
+position locked.p;
+identifier lock,unlock;
+expression x <= locked.E1;
+expression E,locked.E1;
+expression E2;
+@@
+
+if (E) {
+ <+... when != E1
+ lock(E1@p,...)
+ ...+>
+}
+... when != E1
+    when != \(x = E2\|&x\)
+    when forall
+if (E) {
+ <+... when != E1
+ unlock@p1(E1,...)
+ ...+>
+}
+
+@r depends on !balanced 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,...);
+
+@script:python depends on org@
+p1 << r.p1;
+p2 << r.p2;
+lock << r.lock;
+@@
+
+cocci.print_main(lock,p1)
+cocci.print_secs("second lock",p2)
+
+@script:python depends on report@
+p1 << r.p1;
+p2 << r.p2;
+lock << r.lock;
+@@
+
+msg = "second lock on line %s" % (p2[0].line)
+coccilib.report.print_report(p1[0],msg)