1 files changed, 48 insertions, 0 deletions
diff --git a/debian/patches-rt/0003-rtmutex-Add-a-special-case-for-ww-mutex-handling.patch b/debian/patches-rt/0003-rtmutex-Add-a-special-case-for-ww-mutex-handling.patch
new file mode 100644
index 000000000..017012785
--- /dev/null
+++ b/debian/patches-rt/0003-rtmutex-Add-a-special-case-for-ww-mutex-handling.patch
@@ -0,0 +1,48 @@
+From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+Date: Fri, 13 Aug 2021 12:40:49 +0200
+Subject: [PATCH 03/10] rtmutex: Add a special case for ww-mutex handling.
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.3-rt21.tar.xz
+
+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 <bigeasy@linutronix.de>
+---
+ 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;