[PATCH 3/4] test-ww_mutex: Handle transient -EDEADLK in test_cycle_work

[Håkon Bugge]

There is a timing issue in test_cycle_work(), in the sense that
acquiring *a_mutex* after deadlock has been detected on the *b_mutex*,
may not succeed immediately. This may lead to false negatives, which
shows up in the log as:

   cyclic deadlock not resolved, ret[77/93] = -35

We fix that by re-trying until the lock is acquired.

Fixes: d1b42b800e5d ("locking/ww_mutex: Add kselftests for resolving ww_mutex cyclic deadlocks")
Fixes: e4a02ed2aaf4 ("locking/ww_mutex: Fix runtime warning in the WW mutex selftest")
Signed-off-by: Håkon Bugge <haakon.bugge@xxxxxxxxxx>
---
 kernel/locking/test-ww_mutex.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 5a4c92801bdfb..6b29a7a8f5fba 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -306,7 +306,9 @@ static void test_cycle_work(struct work_struct *work)
 		err = 0;
 		ww_mutex_unlock(&cycle->a_mutex);
 		ww_mutex_lock_slow(cycle->b_mutex, &ctx);
-		erra = ww_mutex_lock(&cycle->a_mutex, &ctx);
+		do {
+			erra = ww_mutex_lock(&cycle->a_mutex, &ctx);
+		} while (erra == -EDEADLK);
 	}
 
 	if (!err)
-- 
2.43.5