[PATCH drm-misc-next v9 01/11] drm/gem: fix lockdep check for dma-resv lock

[Danilo Krummrich <dakr@redhat.com>]

When no custom lock is set to protect a GEMs GPUVA list, lockdep checks
should fall back to the GEM objects dma-resv lock. With the current
implementation we're setting the lock_dep_map of the GEM objects 'resv'
pointer (in case no custom lock_dep_map is set yet) on
drm_gem_private_object_init().

However, the GEM objects 'resv' pointer might still change after
drm_gem_private_object_init() is called, e.g. through
ttm_bo_init_reserved(). This can result in the wrong lock being tracked.

To fix this, call dma_resv_held() directly from
drm_gem_gpuva_assert_lock_held() and fall back to the GEMs lock_dep_map
pointer only if an actual custom lock is set.

Fixes: e6303f323b1a ("drm: manager to keep track of GPUs VA mappings")
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
---
 include/drm/drm_gem.h | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
index c0b13c43b459..bc9f6aa2f3fe 100644
--- a/include/drm/drm_gem.h
+++ b/include/drm/drm_gem.h
@@ -551,15 +551,17 @@ int drm_gem_evict(struct drm_gem_object *obj);
  * @lock: the lock used to protect the gpuva list. The locking primitive
  * must contain a dep_map field.
  *
- * Call this if you're not proctecting access to the gpuva list
- * with the dma-resv lock, otherwise, drm_gem_gpuva_init() takes care
- * of initializing lock_dep_map for you.
+ * Call this if you're not proctecting access to the gpuva list with the
+ * dma-resv lock, but with a custom lock.
  */
 #define drm_gem_gpuva_set_lock(obj, lock) \
-	if (!(obj)->gpuva.lock_dep_map) \
+	if (!WARN((obj)->gpuva.lock_dep_map, \
+		  "GEM GPUVA lock should be set only once.")) \
 		(obj)->gpuva.lock_dep_map = &(lock)->dep_map
 #define drm_gem_gpuva_assert_lock_held(obj) \
-	lockdep_assert(lock_is_held((obj)->gpuva.lock_dep_map))
+	lockdep_assert((obj)->gpuva.lock_dep_map ? \
+		       lock_is_held((obj)->gpuva.lock_dep_map) : \
+		       dma_resv_held((obj)->resv))
 #else
 #define drm_gem_gpuva_set_lock(obj, lock) do {} while (0)
 #define drm_gem_gpuva_assert_lock_held(obj) do {} while (0)
@@ -573,11 +575,12 @@ int drm_gem_evict(struct drm_gem_object *obj);
  *
  * Calling this function is only necessary for drivers intending to support the
  * &drm_driver_feature DRIVER_GEM_GPUVA.
+ *
+ * See also drm_gem_gpuva_set_lock().
  */
 static inline void drm_gem_gpuva_init(struct drm_gem_object *obj)
 {
 	INIT_LIST_HEAD(&obj->gpuva.list);
-	drm_gem_gpuva_set_lock(obj, &obj->resv->lock.base);
 }
 
 /**
-- 
2.41.0