PREEMPT_RT has a different locking implementation for ww_mutex. The
base mutex of struct ww_mutex is declared as struct WW_MUTEX_BASE. The
latter is defined as `mutex' for non-PREEMPT_RT builds and `rt_mutex'
for PREEMPT_RT builds.

Using mutex_lock() directly on the base mutex in
ttm_bo_reserve_deadlock() leads to compile error on PREEMPT_RT.

The locking-selftest has its own defines to deal with this and it is
probably best to defines the needed one within the test program since
their usefulness is limited outside of well known selftests.

Provide ww_mutex_base_lock() which points to the correct function for
PREEMPT_RT and non-PREEMPT_RT builds.

Fixes: 995279d280d1e ("drm/ttm/tests: Add tests for ttm_bo functions")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---

I posted this path https://lore.kernel.org/r/20240404102534.QTa80QPY@linutronix.de
Then I reposted it https://lore.kernel.org/r/20240613064716.WxAIvb9K@linutronix.de
and learned from Christian Koenig that can't review it.

Could someone please add it their tree (drm, locking, misc, akpm) so
that it gets merged upstream?

 drivers/gpu/drm/ttm/tests/ttm_bo_test.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

--- a/drivers/gpu/drm/ttm/tests/ttm_bo_test.c
+++ b/drivers/gpu/drm/ttm/tests/ttm_bo_test.c
@@ -18,6 +18,12 @@
 
 #define BO_SIZE		SZ_8K
 
+#ifdef CONFIG_PREEMPT_RT
+#define ww_mutex_base_lock(b)			rt_mutex_lock(b)
+#else
+#define ww_mutex_base_lock(b)			mutex_lock(b)
+#endif
+
 struct ttm_bo_test_case {
 	const char *description;
 	bool interruptible;
@@ -142,7 +148,7 @@ static void ttm_bo_reserve_deadlock(stru
 	bo2 = ttm_bo_kunit_init(test, test->priv, BO_SIZE);
 
 	ww_acquire_init(&ctx1, &reservation_ww_class);
-	mutex_lock(&bo2->base.resv->lock.base);
+	ww_mutex_base_lock(&bo2->base.resv->lock.base);
 
 	/* The deadlock will be caught by WW mutex, don't warn about it */
 	lock_release(&bo2->base.resv->lock.base.dep_map, 1);

On Wed, 19 Jun 2024 16:46:30 +0200, Sebastian Andrzej Siewior wrote:
> PREEMPT_RT has a different locking implementation for ww_mutex. The
> base mutex of struct ww_mutex is declared as struct WW_MUTEX_BASE. The
> latter is defined as `mutex' for non-PREEMPT_RT builds and `rt_mutex'
> for PREEMPT_RT builds.
> 
> Using mutex_lock() directly on the base mutex in
> ttm_bo_reserve_deadlock() leads to compile error on PREEMPT_RT.
> 
> [...]

Applied to misc/kernel.git (drm-misc-next).

Thanks!
Maxime