drm/i915: Move dev_priv->mm.[un]bound_list to its own lock

Remove the struct_mutex requirement around dev_priv->mm.bound_list and
dev_priv->mm.unbound_list by giving it its own spinlock. This reduces
one more requirement for struct_mutex and in the process gives us
slightly more accurate unbound_list tracking, which should improve the
shrinker - but the drawback is that we drop the retirement before
counting so i915_gem_object_is_active() may be stale and lead us to
underestimate the number of objects that may be shrunk (see commit
bed50ae ("drm/i915/shrinker: Flush active on objects before
counting")).

v2: Crosslink the spinlock to the lists it protects, and btw this
changes s/obj->global_link/obj->mm.link/
v3: Fix decoupling of old links in i915_gem_object_attach_phys()
v3.1: Fix the fix, only unlink if it was linked
v3.2: Use a local for to_i915(obj->base.dev)->mm.obj_lock

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171016114037.5556-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -271,7 +271,9 @@ static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
 		goto out;
 
 	total_obj_size = total_gtt_size = count = 0;
-	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_link) {
+
+	spin_lock(&dev_priv->mm.obj_lock);
+	list_for_each_entry(obj, &dev_priv->mm.bound_list, mm.link) {
 		if (count == total)
 			break;
 
@@ -283,7 +285,7 @@ static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
 		total_gtt_size += i915_gem_obj_total_ggtt_size(obj);
 
 	}
-	list_for_each_entry(obj, &dev_priv->mm.unbound_list, global_link) {
+	list_for_each_entry(obj, &dev_priv->mm.unbound_list, mm.link) {
 		if (count == total)
 			break;
 
@@ -293,6 +295,7 @@ static int i915_gem_stolen_list_info(struct seq_file *m, void *data)
 		objects[count++] = obj;
 		total_obj_size += obj->base.size;
 	}
+	spin_unlock(&dev_priv->mm.obj_lock);
 
 	sort(objects, count, sizeof(*objects), obj_rank_by_stolen, NULL);
 
@@ -454,7 +457,9 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
 	mapped_size = mapped_count = 0;
 	purgeable_size = purgeable_count = 0;
 	huge_size = huge_count = 0;
-	list_for_each_entry(obj, &dev_priv->mm.unbound_list, global_link) {
+
+	spin_lock(&dev_priv->mm.obj_lock);
+	list_for_each_entry(obj, &dev_priv->mm.unbound_list, mm.link) {
 		size += obj->base.size;
 		++count;
 
@@ -477,7 +482,7 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
 	seq_printf(m, "%u unbound objects, %llu bytes\n", count, size);
 
 	size = count = dpy_size = dpy_count = 0;
-	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_link) {
+	list_for_each_entry(obj, &dev_priv->mm.bound_list, mm.link) {
 		size += obj->base.size;
 		++count;
 
@@ -502,6 +507,8 @@ static int i915_gem_object_info(struct seq_file *m, void *data)
 			page_sizes |= obj->mm.page_sizes.sg;
 		}
 	}
+	spin_unlock(&dev_priv->mm.obj_lock);
+
 	seq_printf(m, "%u bound objects, %llu bytes\n",
 		   count, size);
 	seq_printf(m, "%u purgeable objects, %llu bytes\n",
@@ -568,28 +575,46 @@ static int i915_gem_gtt_info(struct seq_file *m, void *data)
 	struct drm_info_node *node = m->private;
 	struct drm_i915_private *dev_priv = node_to_i915(node);
 	struct drm_device *dev = &dev_priv->drm;
+	struct drm_i915_gem_object **objects;
 	struct drm_i915_gem_object *obj;
 	u64 total_obj_size, total_gtt_size;
+	unsigned long nobject, n;
 	int count, ret;
 
+	nobject = READ_ONCE(dev_priv->mm.object_count);
+	objects = kvmalloc_array(nobject, sizeof(*objects), GFP_KERNEL);
+	if (!objects)
+		return -ENOMEM;
+
 	ret = mutex_lock_interruptible(&dev->struct_mutex);
 	if (ret)
 		return ret;
 
-	total_obj_size = total_gtt_size = count = 0;
-	list_for_each_entry(obj, &dev_priv->mm.bound_list, global_link) {
+	count = 0;
+	spin_lock(&dev_priv->mm.obj_lock);
+	list_for_each_entry(obj, &dev_priv->mm.bound_list, mm.link) {
+		objects[count++] = obj;
+		if (count == nobject)
+			break;
+	}
+	spin_unlock(&dev_priv->mm.obj_lock);
+
+	total_obj_size = total_gtt_size = 0;
+	for (n = 0;  n < count; n++) {
+		obj = objects[n];
+
 		seq_puts(m, "   ");
 		describe_obj(m, obj);
 		seq_putc(m, '\n');
 		total_obj_size += obj->base.size;
 		total_gtt_size += i915_gem_obj_total_ggtt_size(obj);
-		count++;
 	}
 
 	mutex_unlock(&dev->struct_mutex);
 
 	seq_printf(m, "Total %d objects, %llu bytes, %llu GTT size\n",
 		   count, total_obj_size, total_gtt_size);
+	kvfree(objects);
 
 	return 0;
 }

drivers/gpu/drm/i915/i915_drv.h

@@ -1490,6 +1490,9 @@ struct i915_gem_mm {
 	 * always the inner lock when overlapping with struct_mutex. */
 	struct mutex stolen_lock;
 
+	/* Protects bound_list/unbound_list and #drm_i915_gem_object.mm.link */
+	spinlock_t obj_lock;
+
 	/** List of all objects in gtt_space. Used to restore gtt
 	 * mappings on resume */
 	struct list_head bound_list;

drivers/gpu/drm/i915/i915_gem.c

@@ -1537,6 +1537,8 @@ static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
 	struct list_head *list;
 	struct i915_vma *vma;
 
+	GEM_BUG_ON(!i915_gem_object_has_pinned_pages(obj));
+
 	list_for_each_entry(vma, &obj->vma_list, obj_link) {
 		if (!i915_vma_is_ggtt(vma))
 			break;
@@ -1551,8 +1553,10 @@ static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
 	}
 
 	i915 = to_i915(obj->base.dev);
+	spin_lock(&i915->mm.obj_lock);
 	list = obj->bind_count ? &i915->mm.bound_list : &i915->mm.unbound_list;
-	list_move_tail(&obj->global_link, list);
+	list_move_tail(&obj->mm.link, list);
+	spin_unlock(&i915->mm.obj_lock);
 }
 
 /**
@@ -2253,6 +2257,7 @@ static void __i915_gem_object_reset_page_iter(struct drm_i915_gem_object *obj)
 void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
 				 enum i915_mm_subclass subclass)
 {
+	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	struct sg_table *pages;
 
 	if (i915_gem_object_has_pinned_pages(obj))
@@ -2273,6 +2278,10 @@ void __i915_gem_object_put_pages(struct drm_i915_gem_object *obj,
 	pages = fetch_and_zero(&obj->mm.pages);
 	GEM_BUG_ON(!pages);
 
+	spin_lock(&i915->mm.obj_lock);
+	list_del(&obj->mm.link);
+	spin_unlock(&i915->mm.obj_lock);
+
 	if (obj->mm.mapping) {
 		void *ptr;
 
@@ -2507,7 +2516,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 	obj->mm.pages = pages;
 
 	if (i915_gem_object_is_tiled(obj) &&
-	    to_i915(obj->base.dev)->quirks & QUIRK_PIN_SWIZZLED_PAGES) {
+	    i915->quirks & QUIRK_PIN_SWIZZLED_PAGES) {
 		GEM_BUG_ON(obj->mm.quirked);
 		__i915_gem_object_pin_pages(obj);
 		obj->mm.quirked = true;
@@ -2529,8 +2538,11 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 		if (obj->mm.page_sizes.phys & ~0u << i)
 			obj->mm.page_sizes.sg |= BIT(i);
 	}
-
 	GEM_BUG_ON(!HAS_PAGE_SIZES(i915, obj->mm.page_sizes.sg));
+
+	spin_lock(&i915->mm.obj_lock);
+	list_add(&obj->mm.link, &i915->mm.unbound_list);
+	spin_unlock(&i915->mm.obj_lock);
 }
 
 static int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
@@ -4324,7 +4336,6 @@ void i915_gem_object_init(struct drm_i915_gem_object *obj,
 {
 	mutex_init(&obj->mm.lock);
 
-	INIT_LIST_HEAD(&obj->global_link);
 	INIT_LIST_HEAD(&obj->vma_list);
 	INIT_LIST_HEAD(&obj->lut_list);
 	INIT_LIST_HEAD(&obj->batch_pool_link);
@@ -4496,7 +4507,18 @@ static void __i915_gem_free_objects(struct drm_i915_private *i915,
 		GEM_BUG_ON(!list_empty(&obj->vma_list));
 		GEM_BUG_ON(!RB_EMPTY_ROOT(&obj->vma_tree));
 
-		list_del(&obj->global_link);
+		/* This serializes freeing with the shrinker. Since the free
+		 * is delayed, first by RCU then by the workqueue, we want the
+		 * shrinker to be able to free pages of unreferenced objects,
+		 * or else we may oom whilst there are plenty of deferred
+		 * freed objects.
+		 */
+		if (i915_gem_object_has_pages(obj)) {
+			spin_lock(&i915->mm.obj_lock);
+			list_del_init(&obj->mm.link);
+			spin_unlock(&i915->mm.obj_lock);
+		}
+
 	}
 	intel_runtime_pm_put(i915);
 	mutex_unlock(&i915->drm.struct_mutex);
@@ -5035,11 +5057,14 @@ i915_gem_load_init(struct drm_i915_private *dev_priv)
 		goto err_priorities;
 
 	INIT_WORK(&dev_priv->mm.free_work, __i915_gem_free_work);
+
+	spin_lock_init(&dev_priv->mm.obj_lock);
 	init_llist_head(&dev_priv->mm.free_list);
 	INIT_LIST_HEAD(&dev_priv->mm.unbound_list);
 	INIT_LIST_HEAD(&dev_priv->mm.bound_list);
 	INIT_LIST_HEAD(&dev_priv->mm.fence_list);
 	INIT_LIST_HEAD(&dev_priv->mm.userfault_list);
+
 	INIT_DELAYED_WORK(&dev_priv->gt.retire_work,
 			  i915_gem_retire_work_handler);
 	INIT_DELAYED_WORK(&dev_priv->gt.idle_work,
@@ -5133,12 +5158,12 @@ int i915_gem_freeze_late(struct drm_i915_private *dev_priv)
 	i915_gem_shrink(dev_priv, -1UL, NULL, I915_SHRINK_UNBOUND);
 	i915_gem_drain_freed_objects(dev_priv);
 
-	mutex_lock(&dev_priv->drm.struct_mutex);
+	spin_lock(&dev_priv->mm.obj_lock);
 	for (p = phases; *p; p++) {
-		list_for_each_entry(obj, *p, global_link)
+		list_for_each_entry(obj, *p, mm.link)
 			__start_cpu_write(obj);
 	}
-	mutex_unlock(&dev_priv->drm.struct_mutex);
+	spin_unlock(&dev_priv->mm.obj_lock);
 
 	return 0;
 }
@@ -5457,7 +5482,17 @@ int i915_gem_object_attach_phys(struct drm_i915_gem_object *obj, int align)
 		goto err_unlock;
 	}
 
-	pages = obj->mm.pages;
+	pages = fetch_and_zero(&obj->mm.pages);
+	if (pages) {
+		struct drm_i915_private *i915 = to_i915(obj->base.dev);
+
+		__i915_gem_object_reset_page_iter(obj);
+
+		spin_lock(&i915->mm.obj_lock);
+		list_del(&obj->mm.link);
+		spin_unlock(&i915->mm.obj_lock);
+	}
+
 	obj->ops = &i915_gem_phys_ops;
 
 	err = ____i915_gem_object_get_pages(obj);

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -3594,8 +3594,7 @@ void i915_gem_restore_gtt_mappings(struct drm_i915_private *dev_priv)
 	ggtt->base.closed = true; /* skip rewriting PTE on VMA unbind */
 
 	/* clflush objects bound into the GGTT and rebind them. */
-	list_for_each_entry_safe(obj, on,
-				 &dev_priv->mm.bound_list, global_link) {
+	list_for_each_entry_safe(obj, on, &dev_priv->mm.bound_list, mm.link) {
 		bool ggtt_bound = false;
 		struct i915_vma *vma;
 

drivers/gpu/drm/i915/i915_gem_object.h

@@ -114,7 +114,6 @@ struct drm_i915_gem_object {
 
 	/** Stolen memory for this object, instead of being backed by shmem. */
 	struct drm_mm_node *stolen;
-	struct list_head global_link;
 	union {
 		struct rcu_head rcu;
 		struct llist_node freed;
@@ -208,6 +207,12 @@ struct drm_i915_gem_object {
 			struct mutex lock; /* protects this cache */
 		} get_page;
 
+		/**
+		 * Element within i915->mm.unbound_list or i915->mm.bound_list,
+		 * locked by i915->mm.obj_lock.
+		 */
+		struct list_head link;
+
 		/**
 		 * Advice: are the backing pages purgeable?
 		 */