Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Maarten Lankhorst <d...@mblankhorst.nl>
Cc: Nicolai Hähnle <nhaeh...@gmail.com>
---
 kernel/locking/test-ww_mutex.c | 98 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 835fa7a1036e..5a643ba2b020 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -153,6 +153,96 @@ static int test_aa(void)
        return ret;
 }
 
+struct test_abba {
+       struct work_struct work;
+       struct ww_mutex a_mutex;
+       struct ww_mutex b_mutex;
+       struct completion a_ready;
+       struct completion b_ready;
+       bool resolve;
+       int result;
+};
+
+static void test_abba_work(struct work_struct *work)
+{
+       struct test_abba *abba = container_of(work, typeof(*abba), work);
+       struct ww_acquire_ctx ctx;
+       int err;
+
+       ww_acquire_init(&ctx, &ww_class);
+       ww_mutex_lock(&abba->b_mutex, &ctx);
+
+       complete(&abba->b_ready);
+       wait_for_completion(&abba->a_ready);
+
+       err = ww_mutex_lock(&abba->a_mutex, &ctx);
+       if (abba->resolve && err == -EDEADLK) {
+               ww_mutex_unlock(&abba->b_mutex);
+               ww_mutex_lock_slow(&abba->a_mutex, &ctx);
+               err = ww_mutex_lock(&abba->b_mutex, &ctx);
+       }
+
+       if (!err)
+               ww_mutex_unlock(&abba->a_mutex);
+       ww_mutex_unlock(&abba->b_mutex);
+       ww_acquire_fini(&ctx);
+
+       abba->result = err;
+}
+
+static int test_abba(bool resolve)
+{
+       struct test_abba abba;
+       struct ww_acquire_ctx ctx;
+       int err, ret;
+
+       ww_mutex_init(&abba.a_mutex, &ww_class);
+       ww_mutex_init(&abba.b_mutex, &ww_class);
+       INIT_WORK_ONSTACK(&abba.work, test_abba_work);
+       init_completion(&abba.a_ready);
+       init_completion(&abba.b_ready);
+       abba.resolve = resolve;
+
+       schedule_work(&abba.work);
+
+       ww_acquire_init(&ctx, &ww_class);
+       ww_mutex_lock(&abba.a_mutex, &ctx);
+
+       complete(&abba.a_ready);
+       wait_for_completion(&abba.b_ready);
+
+       err = ww_mutex_lock(&abba.b_mutex, &ctx);
+       if (resolve && err == -EDEADLK) {
+               ww_mutex_unlock(&abba.a_mutex);
+               ww_mutex_lock_slow(&abba.b_mutex, &ctx);
+               err = ww_mutex_lock(&abba.a_mutex, &ctx);
+       }
+
+       if (!err)
+               ww_mutex_unlock(&abba.b_mutex);
+       ww_mutex_unlock(&abba.a_mutex);
+       ww_acquire_fini(&ctx);
+
+       flush_work(&abba.work);
+       destroy_work_on_stack(&abba.work);
+
+       ret = 0;
+       if (resolve) {
+               if (err || abba.result) {
+                       pr_err("%s: failed to resolve ABBA deadlock, A err=%d, 
B err=%d\n",
+                              __func__, err, abba.result);
+                       ret = -EINVAL;
+               }
+       } else {
+               if (err != -EDEADLK && abba.result != -EDEADLK) {
+                       pr_err("%s: missed ABBA deadlock, A err=%d, B err=%d\n",
+                              __func__, err, abba.result);
+                       ret = -EINVAL;
+               }
+       }
+       return ret;
+}
+
 static int __init test_ww_mutex_init(void)
 {
        int ret;
@@ -165,6 +255,14 @@ static int __init test_ww_mutex_init(void)
        if (ret)
                return ret;
 
+       ret = test_abba(false);
+       if (ret)
+               return ret;
+
+       ret = test_abba(true);
+       if (ret)
+               return ret;
+
        return 0;
 }
 
-- 
2.10.2

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