drm/i915: Make shrink/unshrink be atomic

Add an atomic counter and always take the spinlock around the pin/unpin
events, so that we can perform the list manipulation concurrently.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190910212204.17190-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_domain.c

@@ -494,7 +494,8 @@ static void i915_gem_object_bump_inactive_ggtt(struct drm_i915_gem_object *obj)
 
 		spin_lock_irqsave(&i915->mm.obj_lock, flags);
 
-		if (obj->mm.madv == I915_MADV_WILLNEED)
+		if (obj->mm.madv == I915_MADV_WILLNEED &&
+		    !atomic_read(&obj->mm.shrink_pin))
 			list_move_tail(&obj->mm.link, &i915->mm.shrink_list);
 
 		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -156,6 +156,7 @@ struct drm_i915_gem_object {
 	struct {
 		struct mutex lock; /* protects the pages and their use */
 		atomic_t pages_pin_count;
+		atomic_t shrink_pin;
 
 		struct sg_table *pages;
 		void *mapping;

drivers/gpu/drm/i915/gem/i915_gem_pages.c

@@ -71,6 +71,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 			list = &i915->mm.shrink_list;
 		list_add_tail(&obj->mm.link, list);
 
+		atomic_set(&obj->mm.shrink_pin, 0);
 		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
 	}
 }

drivers/gpu/drm/i915/gem/i915_gem_shrinker.c

@@ -516,46 +516,52 @@ void i915_gem_shrinker_taints_mutex(struct drm_i915_private *i915,
 
 void i915_gem_object_make_unshrinkable(struct drm_i915_gem_object *obj)
 {
+	struct drm_i915_private *i915 = obj_to_i915(obj);
+	unsigned long flags;
+
 	/*
 	 * We can only be called while the pages are pinned or when
 	 * the pages are released. If pinned, we should only be called
 	 * from a single caller under controlled conditions; and on release
 	 * only one caller may release us. Neither the two may cross.
 	 */
-	if (!list_empty(&obj->mm.link)) { /* pinned by caller */
-		struct drm_i915_private *i915 = obj_to_i915(obj);
-		unsigned long flags;
-
-		spin_lock_irqsave(&i915->mm.obj_lock, flags);
-		GEM_BUG_ON(list_empty(&obj->mm.link));
+	if (atomic_add_unless(&obj->mm.shrink_pin, 1, 0))
+		return;
 
+	spin_lock_irqsave(&i915->mm.obj_lock, flags);
+	if (!atomic_fetch_inc(&obj->mm.shrink_pin) &&
+	    !list_empty(&obj->mm.link)) {
 		list_del_init(&obj->mm.link);
 		i915->mm.shrink_count--;
 		i915->mm.shrink_memory -= obj->base.size;
-
-		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
 	}
+	spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
 }
 
 static void __i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj,
 					      struct list_head *head)
 {
+	struct drm_i915_private *i915 = obj_to_i915(obj);
+	unsigned long flags;
+
 	GEM_BUG_ON(!i915_gem_object_has_pages(obj));
-	GEM_BUG_ON(!list_empty(&obj->mm.link));
+	if (!i915_gem_object_is_shrinkable(obj))
+		return;
 
-	if (i915_gem_object_is_shrinkable(obj)) {
-		struct drm_i915_private *i915 = obj_to_i915(obj);
-		unsigned long flags;
+	if (atomic_add_unless(&obj->mm.shrink_pin, -1, 1))
+		return;
 
-		spin_lock_irqsave(&i915->mm.obj_lock, flags);
-		GEM_BUG_ON(!kref_read(&obj->base.refcount));
+	spin_lock_irqsave(&i915->mm.obj_lock, flags);
+	GEM_BUG_ON(!kref_read(&obj->base.refcount));
+	if (atomic_dec_and_test(&obj->mm.shrink_pin)) {
+		GEM_BUG_ON(!list_empty(&obj->mm.link));
 
 		list_add_tail(&obj->mm.link, head);
 		i915->mm.shrink_count++;
 		i915->mm.shrink_memory += obj->base.size;
 
-		spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
 	}
+	spin_unlock_irqrestore(&i915->mm.obj_lock, flags);
 }
 
 void i915_gem_object_make_shrinkable(struct drm_i915_gem_object *obj)

drivers/gpu/drm/i915/gt/intel_context.c

@@ -134,8 +134,8 @@ static int __context_pin_state(struct i915_vma *vma)
 
 static void __context_unpin_state(struct i915_vma *vma)
 {
-	__i915_vma_unpin(vma);
 	i915_vma_make_shrinkable(vma);
+	__i915_vma_unpin(vma);
 }
 
 static void __intel_context_retire(struct i915_active *active)