Subject: [PATCH 03/10] rtmutex: Add a special case for ww-mutex handling.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Fri, 13 Aug 2021 12:40:49 +0200

The lockdep selftest for ww-mutex assumes in a few cases the
ww_ctx->contending_lock assignment via __ww_mutex_check_kill() which
does not happen if the rtmutex detects the deadlock early.

The testcase passes if the deadlock handling here is removed. This means
that it will work if multiple threads/tasks are involved and not just a
single one.

Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/locking/rtmutex.c |   20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1097,8 +1097,26 @@ static int __sched task_blocks_on_rt_mut
 	 * which is wrong, as the other waiter is not in a deadlock
 	 * situation.
 	 */
-	if (owner == task)
+	if (owner == task) {
+#if defined(DEBUG_WW_MUTEXES) && defined(CONFIG_DEBUG_LOCKING_API_SELFTESTS)
+		/*
+		 * The lockdep selftest for ww-mutex assumes in a few cases
+		 * the ww_ctx->contending_lock assignment via
+		 * __ww_mutex_check_kill() which does not happen if the rtmutex
+		 * detects the deadlock early.
+		 */
+		if (build_ww_mutex() && ww_ctx) {
+			struct rt_mutex *rtm;
+
+			/* Check whether the waiter should backout immediately */
+			rtm = container_of(lock, struct rt_mutex, rtmutex);
+
+			__ww_mutex_add_waiter(waiter, rtm, ww_ctx);
+			__ww_mutex_check_kill(rtm, waiter, ww_ctx);
+		}
+#endif
 		return -EDEADLK;
+	}
 
 	raw_spin_lock(&task->pi_lock);
 	waiter->task = task;