[RFC][PATCH 2/4] locktorture: Add nested locking to mutex torture tests

[John Stultz <jstultz@google.com>]

This patch adds randomized nested locking to the mutex torture
tests.

This was inspired by locktorture extensions originally implemented
by Connor O'Brien, for stress testing the proxy-execution series:
  https://lore.kernel.org/lkml/20221003214501.2050087-12-connoro@google.com/

Comments or feedback would be greatly appreciated!

Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
 kernel/locking/locktorture.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index f4fbd3194654..27d92ce36836 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -332,6 +332,28 @@ static struct lock_torture_ops rw_lock_irq_ops = {
 };
 
 static DEFINE_MUTEX(torture_mutex);
+static struct mutex torture_nested_mutexes[MAX_LOCKS];
+static struct lock_class_key nested_mutex_keys[MAX_LOCKS];
+
+static void torture_mutex_init(void)
+{
+	int i;
+
+	for (i = 0; i < MAX_LOCKS; i++)
+		__mutex_init(&torture_nested_mutexes[i], __func__,
+			     &nested_mutex_keys[i]);
+}
+
+static int torture_mutex_nested_lock(int tid __maybe_unused,
+				     u32 lockset)
+{
+	int i;
+
+	for (i = 0; i < nlocks; i++)
+		if (lockset & (1 << i))
+			mutex_lock(&torture_nested_mutexes[i]);
+	return 0;
+}
 
 static int torture_mutex_lock(int tid __maybe_unused)
 __acquires(torture_mutex)
@@ -360,11 +382,24 @@ __releases(torture_mutex)
 	mutex_unlock(&torture_mutex);
 }
 
+static void torture_mutex_nested_unlock(int tid __maybe_unused,
+					u32 lockset)
+{
+	int i;
+
+	for (i = nlocks - 1; i >= 0; i--)
+		if (lockset & (1 << i))
+			mutex_unlock(&torture_nested_mutexes[i]);
+}
+
 static struct lock_torture_ops mutex_lock_ops = {
+	.init		= torture_mutex_init,
+	.nested_lock	= torture_mutex_nested_lock,
 	.writelock	= torture_mutex_lock,
 	.write_delay	= torture_mutex_delay,
 	.task_boost     = torture_boost_dummy,
 	.writeunlock	= torture_mutex_unlock,
+	.nested_unlock	= torture_mutex_nested_unlock,
 	.readlock       = NULL,
 	.read_delay     = NULL,
 	.readunlock     = NULL,
-- 
2.39.1.519.gcb327c4b5f-goog