[PATCH 2/4] lockdep/selftests: Add mixed read-write ABBA tests

From: Peter Zijlstra
Date: Wed Aug 23 2017 - 08:18:39 EST


Currently lockdep has limited support for recursive readers, add a few
mixed read-write ABBA selftests to show the extend of these
limitations.

[ 0.000000] ----------------------------------------------------------------------------
[ 0.000000] | spin |wlock |rlock |mutex | wsem | rsem |
[ 0.000000] --------------------------------------------------------------------------

[ 0.000000] mixed read-lock/lock-write ABBA: |FAILED| | ok |
[ 0.000000] mixed read-lock/lock-read ABBA: | ok | | ok |
[ 0.000000] mixed write-lock/lock-write ABBA: | ok | | ok |

This clearly illustrates the case where lockdep fails to find a
deadlock.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -363,6 +363,103 @@ static void rsem_AA3(void)
}

/*
+ * read_lock(A)
+ * spin_lock(B)
+ * spin_lock(B)
+ * write_lock(A)
+ */
+static void rlock_ABBA1(void)
+{
+ RL(X1);
+ L(Y1);
+ U(Y1);
+ RU(X1);
+
+ L(Y1);
+ WL(X1);
+ WU(X1);
+ U(Y1); // should fail
+}
+
+static void rwsem_ABBA1(void)
+{
+ RSL(X1);
+ ML(Y1);
+ MU(Y1);
+ RSU(X1);
+
+ ML(Y1);
+ WSL(X1);
+ WSU(X1);
+ MU(Y1); // should fail
+}
+
+/*
+ * read_lock(A)
+ * spin_lock(B)
+ * spin_lock(B)
+ * read_lock(A)
+ */
+static void rlock_ABBA2(void)
+{
+ RL(X1);
+ L(Y1);
+ U(Y1);
+ RU(X1);
+
+ L(Y1);
+ RL(X1);
+ RU(X1);
+ U(Y1); // should NOT fail
+}
+
+static void rwsem_ABBA2(void)
+{
+ RSL(X1);
+ ML(Y1);
+ MU(Y1);
+ RSU(X1);
+
+ ML(Y1);
+ RSL(X1);
+ RSU(X1);
+ MU(Y1); // should fail
+}
+
+
+/*
+ * write_lock(A)
+ * spin_lock(B)
+ * spin_lock(B)
+ * write_lock(A)
+ */
+static void rlock_ABBA3(void)
+{
+ WL(X1);
+ L(Y1);
+ U(Y1);
+ WU(X1);
+
+ L(Y1);
+ WL(X1);
+ WU(X1);
+ U(Y1); // should fail
+}
+
+static void rwsem_ABBA3(void)
+{
+ WSL(X1);
+ ML(Y1);
+ MU(Y1);
+ WSU(X1);
+
+ ML(Y1);
+ WSL(X1);
+ WSU(X1);
+ MU(Y1); // should fail
+}
+
+/*
* ABBA deadlock:
*/

@@ -1056,8 +1153,6 @@ static void dotest(void (*testcase_fn)(v
if (debug_locks != expected) {
unexpected_testcase_failures++;
pr_cont("FAILED|");
-
- dump_stack();
} else {
testcase_successes++;
pr_cont(" ok |");
@@ -1933,6 +2028,24 @@ void locking_selftest(void)
dotest(rsem_AA3, FAILURE, LOCKTYPE_RWSEM);
pr_cont("\n");

+ print_testname("mixed read-lock/lock-write ABBA");
+ pr_cont(" |");
+ dotest(rlock_ABBA1, FAILURE, LOCKTYPE_RWLOCK);
+ pr_cont(" |");
+ dotest(rwsem_ABBA1, FAILURE, LOCKTYPE_RWSEM);
+
+ print_testname("mixed read-lock/lock-read ABBA");
+ pr_cont(" |");
+ dotest(rlock_ABBA2, SUCCESS, LOCKTYPE_RWLOCK);
+ pr_cont(" |");
+ dotest(rwsem_ABBA2, FAILURE, LOCKTYPE_RWSEM);
+
+ print_testname("mixed write-lock/lock-write ABBA");
+ pr_cont(" |");
+ dotest(rlock_ABBA3, FAILURE, LOCKTYPE_RWLOCK);
+ pr_cont(" |");
+ dotest(rwsem_ABBA3, FAILURE, LOCKTYPE_RWSEM);
+
printk(" --------------------------------------------------------------------------\n");

/*