[PATCH 2/2] lockdep/selftest: Add spin_nest_lock test

Boqun Feng
2020-11-02T05:38:15Z

Add a self test case to test the behavior for the following case:

lock(A);
lock_nest_lock(C1, A);
lock(B);
lock_nest_lock(C2, A);

This is a reproducer for a problem[1] reported by Chris Wilson, and is
helpful to prevent this.

[1]: https://lore.kernel.org/lkml/160390684819.31966.12048967113267928793@build.alporthouse.com/

Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
---
lib/locking-selftest.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index afa7d4bb291f..4c24ac8a456c 100644
--- a/lib/locking-selftest.c
+++ b/lib/locking-selftest.c
@@ -2009,6 +2009,19 @@ static void ww_test_spin_nest_unlocked(void)
U(A);
}

+/* This is not a deadlock, because we have X1 to serialize Y1 and Y2 */
+static void ww_test_spin_nest_lock(void)
+{
+ spin_lock(&lock_X1);
+ spin_lock_nest_lock(&lock_Y1, &lock_X1);
+ spin_lock(&lock_A);
+ spin_lock_nest_lock(&lock_Y2, &lock_X1);
+ spin_unlock(&lock_A);
+ spin_unlock(&lock_Y2);
+ spin_unlock(&lock_Y1);
+ spin_unlock(&lock_X1);
+}
+
static void ww_test_unneeded_slow(void)
{
WWAI(&t);
@@ -2226,6 +2239,10 @@ static void ww_tests(void)
dotest(ww_test_spin_nest_unlocked, FAILURE, LOCKTYPE_WW);
pr_cont("\n");

+ print_testname("spinlock nest test");
+ dotest(ww_test_spin_nest_lock, SUCCESS, LOCKTYPE_WW);
+ pr_cont("\n");
+
printk(" -----------------------------------------------------\n");
printk(" |block | try |context|\n");
printk(" -----------------------------------------------------\n");
--
2.28.0