drm/msm/gem: Avoid obj lock in job_run()

Now that everything that controls which LRU an obj lives in *except* the
backing pages is protected by the LRU lock, add a special path to unpin
in the job_run() path, where we are assured that we already have backing
pages and will not be racing against eviction (because the GEM object's
dma_resv contains the fence that will be signaled when the submit/job
completes).
Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527845/
Link: https://lore.kernel.org/r/20230320144356.803762-10-robdclark@gmail.com

drivers/gpu/drm/msm/msm_gem.c

@@ -61,18 +61,14 @@ static void sync_for_cpu(struct msm_gem_object *msm_obj)
 	dma_unmap_sgtable(dev, msm_obj->sgt, DMA_BIDIRECTIONAL, 0);
 }
 
-static void update_lru_locked(struct drm_gem_object *obj)
+static void update_lru_active(struct drm_gem_object *obj)
 {
 	struct msm_drm_private *priv = obj->dev->dev_private;
 	struct msm_gem_object *msm_obj = to_msm_bo(obj);
 
-	msm_gem_assert_locked(&msm_obj->base);
-
-	if (!msm_obj->pages) {
-		GEM_WARN_ON(msm_obj->pin_count);
+	GEM_WARN_ON(!msm_obj->pages);
 
-		drm_gem_lru_move_tail_locked(&priv->lru.unbacked, obj);
-	} else if (msm_obj->pin_count) {
+	if (msm_obj->pin_count) {
 		drm_gem_lru_move_tail_locked(&priv->lru.pinned, obj);
 	} else if (msm_obj->madv == MSM_MADV_WILLNEED) {
 		drm_gem_lru_move_tail_locked(&priv->lru.willneed, obj);
@@ -83,6 +79,22 @@ static void update_lru_locked(struct drm_gem_object *obj)
 	}
 }
 
+static void update_lru_locked(struct drm_gem_object *obj)
+{
+	struct msm_drm_private *priv = obj->dev->dev_private;
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+
+	msm_gem_assert_locked(&msm_obj->base);
+
+	if (!msm_obj->pages) {
+		GEM_WARN_ON(msm_obj->pin_count);
+
+		drm_gem_lru_move_tail_locked(&priv->lru.unbacked, obj);
+	} else {
+		update_lru_active(obj);
+	}
+}
+
 static void update_lru(struct drm_gem_object *obj)
 {
 	struct msm_drm_private *priv = obj->dev->dev_private;
@@ -489,6 +501,24 @@ void msm_gem_unpin_locked(struct drm_gem_object *obj)
 	mutex_unlock(&priv->lru.lock);
 }
 
+/* Special unpin path for use in fence-signaling path, avoiding the need
+ * to hold the obj lock by only depending on things that a protected by
+ * the LRU lock.  In particular we know that that we already have backing
+ * and and that the object's dma_resv has the fence for the current
+ * submit/job which will prevent us racing against page eviction.
+ */
+void msm_gem_unpin_active(struct drm_gem_object *obj)
+{
+	struct msm_drm_private *priv = obj->dev->dev_private;
+	struct msm_gem_object *msm_obj = to_msm_bo(obj);
+
+	mutex_lock(&priv->lru.lock);
+	msm_obj->pin_count--;
+	GEM_WARN_ON(msm_obj->pin_count < 0);
+	update_lru_active(obj);
+	mutex_unlock(&priv->lru.lock);
+}
+
 struct msm_gem_vma *msm_gem_get_vma_locked(struct drm_gem_object *obj,
 					   struct msm_gem_address_space *aspace)
 {

drivers/gpu/drm/msm/msm_gem.h

@@ -128,6 +128,7 @@ struct msm_gem_object {
 uint64_t msm_gem_mmap_offset(struct drm_gem_object *obj);
 int msm_gem_pin_vma_locked(struct drm_gem_object *obj, struct msm_gem_vma *vma);
 void msm_gem_unpin_locked(struct drm_gem_object *obj);
+void msm_gem_unpin_active(struct drm_gem_object *obj);
 struct msm_gem_vma *msm_gem_get_vma_locked(struct drm_gem_object *obj,
 					   struct msm_gem_address_space *aspace);
 int msm_gem_get_iova(struct drm_gem_object *obj,

drivers/gpu/drm/msm/msm_ringbuffer.c

@@ -24,9 +24,7 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
 		struct drm_gem_object *obj = &submit->bos[i].obj->base;
 
 		msm_gem_vma_unpin_fenced(submit->bos[i].vma, fctx);
-		msm_gem_lock(obj);
-		msm_gem_unpin_locked(obj);
-		msm_gem_unlock(obj);
+		msm_gem_unpin_active(obj);
 		submit->bos[i].flags &= ~(BO_VMA_PINNED | BO_OBJ_PINNED);
 	}