drm/msm/gem: Move locking in shrinker path

Move grabbing the bo lock into shrinker, with a msm_gem_trylock() to
skip over bo's that are already locked.  This gets rid of the nested
lock classes.

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

@@ -18,8 +18,6 @@
 #include "msm_gpu.h"
 #include "msm_mmu.h"
 
-static void msm_gem_vunmap_locked(struct drm_gem_object *obj);
-
 
 static dma_addr_t physaddr(struct drm_gem_object *obj)
 {
@@ -692,20 +690,19 @@ int msm_gem_madvise(struct drm_gem_object *obj, unsigned madv)
 	return (madv != __MSM_MADV_PURGED);
 }
 
-void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
+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(!msm_gem_is_locked(obj));
 	WARN_ON(!is_purgeable(msm_obj));
 	WARN_ON(obj->import_attach);
 
-	mutex_lock_nested(&msm_obj->lock, subclass);
-
 	put_iova(obj);
 
-	msm_gem_vunmap_locked(obj);
+	msm_gem_vunmap(obj);
 
 	put_pages(obj);
 
@@ -723,11 +720,9 @@ void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass)
 
 	invalidate_mapping_pages(file_inode(obj->filp)->i_mapping,
 			0, (loff_t)-1);
-
-	msm_gem_unlock(obj);
 }
 
-static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
+void msm_gem_vunmap(struct drm_gem_object *obj)
 {
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
@@ -740,15 +735,6 @@ static void msm_gem_vunmap_locked(struct drm_gem_object *obj)
 	msm_obj->vaddr = NULL;
 }
 
-void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass)
-{
-	struct msm_gem_object *msm_obj = to_msm_bo(obj);
-
-	mutex_lock_nested(&msm_obj->lock, subclass);
-	msm_gem_vunmap_locked(obj);
-	msm_gem_unlock(obj);
-}
-
 /* must be called before _move_to_active().. */
 int msm_gem_sync_object(struct drm_gem_object *obj,
 		struct msm_fence_context *fctx, bool exclusive)
@@ -985,7 +971,7 @@ static void free_object(struct msm_gem_object *msm_obj)
 
 		drm_prime_gem_destroy(obj, msm_obj->sgt);
 	} else {
-		msm_gem_vunmap_locked(obj);
+		msm_gem_vunmap(obj);
 		put_pages(obj);
 	}
 

drivers/gpu/drm/msm/msm_gem.h

@@ -162,6 +162,13 @@ msm_gem_lock(struct drm_gem_object *obj)
 	mutex_lock(&msm_obj->lock);
 }
 
+static inline bool __must_check
+msm_gem_trylock(struct drm_gem_object *obj)
+{
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+	return mutex_trylock(&msm_obj->lock) == 1;
+}
+
 static inline int
 msm_gem_lock_interruptible(struct drm_gem_object *obj)
 {
@@ -190,6 +197,7 @@ static inline bool is_active(struct msm_gem_object *msm_obj)
 
 static inline bool is_purgeable(struct msm_gem_object *msm_obj)
 {
+	WARN_ON(!msm_gem_is_locked(&msm_obj->base));
 	WARN_ON(!mutex_is_locked(&msm_obj->base.dev->struct_mutex));
 	return (msm_obj->madv == MSM_MADV_DONTNEED) && msm_obj->sgt &&
 			!msm_obj->base.dma_buf && !msm_obj->base.import_attach;
@@ -197,27 +205,12 @@ static inline bool is_purgeable(struct msm_gem_object *msm_obj)
 
 static inline bool is_vunmapable(struct msm_gem_object *msm_obj)
 {
+	WARN_ON(!msm_gem_is_locked(&msm_obj->base));
 	return (msm_obj->vmap_count == 0) && msm_obj->vaddr;
 }
 
-/* The shrinker can be triggered while we hold objA->lock, and need
- * to grab objB->lock to purge it.  Lockdep just sees these as a single
- * class of lock, so we use subclasses to teach it the difference.
- *
- * OBJ_LOCK_NORMAL is implicit (ie. normal mutex_lock() call), and
- * OBJ_LOCK_SHRINKER is used by shrinker.
- *
- * It is *essential* that we never go down paths that could trigger the
- * shrinker for a purgable object.  This is ensured by checking that
- * msm_obj->madv == MSM_MADV_WILLNEED.
- */
-enum msm_gem_lock {
-	OBJ_LOCK_NORMAL,
-	OBJ_LOCK_SHRINKER,
-};
-
-void msm_gem_purge(struct drm_gem_object *obj, enum msm_gem_lock subclass);
-void msm_gem_vunmap(struct drm_gem_object *obj, enum msm_gem_lock subclass);
+void msm_gem_purge(struct drm_gem_object *obj);
+void msm_gem_vunmap(struct drm_gem_object *obj);
 void msm_gem_free_work(struct work_struct *work);
 
 /* Created per submit-ioctl, to track bo's and cmdstream bufs, etc,

drivers/gpu/drm/msm/msm_gem_shrinker.c

@@ -52,8 +52,11 @@ msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc)
 		return 0;
 
 	list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
+		if (!msm_gem_trylock(&msm_obj->base))
+			continue;
 		if (is_purgeable(msm_obj))
 			count += msm_obj->base.size >> PAGE_SHIFT;
+		msm_gem_unlock(&msm_obj->base);
 	}
 
 	if (unlock)
@@ -78,10 +81,13 @@ msm_gem_shrinker_scan(struct shrinker *shrinker, struct shrink_control *sc)
 	list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
 		if (freed >= sc->nr_to_scan)
 			break;
+		if (!msm_gem_trylock(&msm_obj->base))
+			continue;
 		if (is_purgeable(msm_obj)) {
-			msm_gem_purge(&msm_obj->base, OBJ_LOCK_SHRINKER);
+			msm_gem_purge(&msm_obj->base);
 			freed += msm_obj->base.size >> PAGE_SHIFT;
 		}
+		msm_gem_unlock(&msm_obj->base);
 	}
 
 	if (unlock)
@@ -107,15 +113,20 @@ msm_gem_shrinker_vmap(struct notifier_block *nb, unsigned long event, void *ptr)
 		return NOTIFY_DONE;
 
 	list_for_each_entry(msm_obj, &priv->inactive_list, mm_list) {
+		if (!msm_gem_trylock(&msm_obj->base))
+			continue;
 		if (is_vunmapable(msm_obj)) {
-			msm_gem_vunmap(&msm_obj->base, OBJ_LOCK_SHRINKER);
-			/* since we don't know any better, lets bail after a few
-			 * and if necessary the shrinker will be invoked again.
-			 * Seems better than unmapping *everything*
-			 */
-			if (++unmapped >= 15)
-				break;
+			msm_gem_vunmap(&msm_obj->base);
+			unmapped++;
 		}
+		msm_gem_unlock(&msm_obj->base);
+
+		/* since we don't know any better, lets bail after a few
+		 * and if necessary the shrinker will be invoked again.
+		 * Seems better than unmapping *everything*
+		 */
+		if (++unmapped >= 15)
+			break;
 	}
 
 	if (unlock)