[tip: locking/core] lockdep/selftest: Add spin_nest_lock test

["tip-bot2 for Boqun Feng" <tip-bot2@linutronix.de>]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     e04ce676e7aa490dcf5df880592e3db5e842a9bc
Gitweb:        https://git.kernel.org/tip/e04ce676e7aa490dcf5df880592e3db5e842a9bc
Author:        Boqun Feng <boqun.feng@gmail.com>
AuthorDate:    Mon, 02 Nov 2020 13:37:42 +08:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 03 Dec 2020 11:20:50 +01:00

lockdep/selftest: Add spin_nest_lock test

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20201102053743.450459-2-boqun.feng@gmail.com
---
 lib/locking-selftest.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/lib/locking-selftest.c b/lib/locking-selftest.c
index afa7d4b..4c24ac8 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");