drm/msm: Drop struct_mutex in shrinker path

Now that the inactive_list is protected by mm_lock, and everything
else on per-obj basis is protected by obj->resv, we no longer depend
on struct_mutex.
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_gem.c

@@ -687,7 +687,6 @@ void msm_gem_purge(struct drm_gem_object *obj)
 	struct drm_device *dev = obj->dev;
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
-	WARN_ON(!mutex_is_locked(&dev->struct_mutex));
 	WARN_ON(!is_purgeable(msm_obj));
 	WARN_ON(obj->import_attach);
 

drivers/gpu/drm/msm/msm_gem_shrinker.c

@@ -8,48 +8,13 @@
 #include "msm_gem.h"
 #include "msm_gpu_trace.h"
 
-static bool msm_gem_shrinker_lock(struct drm_device *dev, bool *unlock)
-{
-	/* NOTE: we are *closer* to being able to get rid of
-	 * mutex_trylock_recursive().. the msm_gem code itself does
-	 * not need struct_mutex, although codepaths that can trigger
-	 * shrinker are still called in code-paths that hold the
-	 * struct_mutex.
-	 *
-	 * Also, msm_obj->madv is protected by struct_mutex.
-	 *
-	 * The next step is probably split out a seperate lock for
-	 * protecting inactive_list, so that shrinker does not need
-	 * struct_mutex.
-	 */
-	switch (mutex_trylock_recursive(&dev->struct_mutex)) {
-	case MUTEX_TRYLOCK_FAILED:
-		return false;
-
-	case MUTEX_TRYLOCK_SUCCESS:
-		*unlock = true;
-		return true;
-
-	case MUTEX_TRYLOCK_RECURSIVE:
-		*unlock = false;
-		return true;
-	}
-
-	BUG();
-}
-
 static unsigned long
 msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 {
 	struct msm_drm_private *priv =
 		container_of(shrinker, struct msm_drm_private, shrinker);
-	struct drm_device *dev = priv->dev;
 	struct msm_gem_object *msm_obj;
 	unsigned long count = 0;
-	bool unlock;
-
-	if (!msm_gem_shrinker_lock(dev, &unlock))
-		return 0;
 
 	mutex_lock(&priv->mm_lock);
 
@@ -63,9 +28,6 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 
 	mutex_unlock(&priv->mm_lock);
 
-	if (unlock)
-		mutex_unlock(&dev->struct_mutex);
-
 	return count;
 }
 
@@ -74,13 +36,8 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 {
 	struct msm_drm_private *priv =
 		container_of(shrinker, struct msm_drm_private, shrinker);
-	struct drm_device *dev = priv->dev;
 	struct msm_gem_object *msm_obj;
 	unsigned long freed = 0;
-	bool unlock;
-
-	if (!msm_gem_shrinker_lock(dev, &unlock))
-		return SHRINK_STOP;
 
 	mutex_lock(&priv->mm_lock);
 
@@ -98,9 +55,6 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 
 	mutex_unlock(&priv->mm_lock);
 
-	if (unlock)
-		mutex_unlock(&dev->struct_mutex);
-
 	if (freed > 0)
 		trace_msm_gem_purge(freed << PAGE_SHIFT);
 
@@ -112,13 +66,8 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
 {
 	struct msm_drm_private *priv =
 		container_of(nb, struct msm_drm_private, vmap_notifier);
-	struct drm_device *dev = priv->dev;
 	struct msm_gem_object *msm_obj;
 	unsigned unmapped = 0;
-	bool unlock;
-
-	if (!msm_gem_shrinker_lock(dev, &unlock))
-		return NOTIFY_DONE;
 
 	mutex_lock(&priv->mm_lock);
 
@@ -141,9 +90,6 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
 
 	mutex_unlock(&priv->mm_lock);
 
-	if (unlock)
-		mutex_unlock(&dev->struct_mutex);
-
 	*(unsigned long *)ptr += unmapped;
 
 	if (unmapped > 0)