drm/i915: Prepare for obj->mm.lock removal, v2.

Stolen objects need to lock, and we may call put_pages when
refcount drops to 0, ensure all calls are handled correctly.

Changes since v1:
- Rebase on top of upstream changes.

Idea-from: Thomas Hellström <thomas.hellstrom@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-33-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -118,6 +118,20 @@ i915_gem_object_put(struct drm_i915_gem_object *obj)
 
 #define assert_object_held(obj) dma_resv_assert_held((obj)->base.resv)
 
+/*
+ * If more than one potential simultaneous locker, assert held.
+ */
+static inline void assert_object_held_shared(struct drm_i915_gem_object *obj)
+{
+	/*
+	 * Note mm list lookup is protected by
+	 * kref_get_unless_zero().
+	 */
+	if (IS_ENABLED(CONFIG_LOCKDEP) &&
+	    kref_read(&obj->base.refcount) > 0)
+		lockdep_assert_held(&obj->mm.lock);
+}
+
 static inline int __i915_gem_object_lock(struct drm_i915_gem_object *obj,
 					 struct i915_gem_ww_ctx *ww,
 					 bool intr)

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

@@ -19,7 +19,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 	bool shrinkable;
 	int i;
 
-	lockdep_assert_held(&obj->mm.lock);
+	assert_object_held_shared(obj);
 
 	if (i915_gem_object_is_volatile(obj))
 		obj->mm.madv = I915_MADV_DONTNEED;
@@ -70,6 +70,7 @@ void __i915_gem_object_set_pages(struct drm_i915_gem_object *obj,
 		struct list_head *list;
 		unsigned long flags;
 
+		lockdep_assert_held(&obj->mm.lock);
 		spin_lock_irqsave(&i915->mm.obj_lock, flags);
 
 		i915->mm.shrink_count++;
@@ -91,6 +92,8 @@ int ____i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 	struct drm_i915_private *i915 = to_i915(obj->base.dev);
 	int err;
 
+	assert_object_held_shared(obj);
+
 	if (unlikely(obj->mm.madv != I915_MADV_WILLNEED)) {
 		drm_dbg(&i915->drm,
 			"Attempting to obtain a purgeable object\n");
@@ -118,6 +121,8 @@ int __i915_gem_object_get_pages(struct drm_i915_gem_object *obj)
 	if (err)
 		return err;
 
+	assert_object_held_shared(obj);
+
 	if (unlikely(!i915_gem_object_has_pages(obj))) {
 		GEM_BUG_ON(i915_gem_object_has_pinned_pages(obj));
 
@@ -145,7 +150,7 @@ void i915_gem_object_truncate(struct drm_i915_gem_object *obj)
 /* Try to discard unwanted pages */
 void i915_gem_object_writeback(struct drm_i915_gem_object *obj)
 {
-	lockdep_assert_held(&obj->mm.lock);
+	assert_object_held_shared(obj);
 	GEM_BUG_ON(i915_gem_object_has_pages(obj));
 
 	if (obj->ops->writeback)
@@ -176,6 +181,8 @@ __i915_gem_object_unset_pages(struct drm_i915_gem_object *obj)
 {
 	struct sg_table *pages;
 
+	assert_object_held_shared(obj);
+
 	pages = fetch_and_zero(&obj->mm.pages);
 	if (IS_ERR_OR_NULL(pages))
 		return pages;
@@ -203,6 +210,9 @@ int __i915_gem_object_put_pages_locked(struct drm_i915_gem_object *obj)
 	if (i915_gem_object_has_pinned_pages(obj))
 		return -EBUSY;
 
+	/* May be called by shrinker from within get_pages() (on another bo) */
+	assert_object_held_shared(obj);
+
 	i915_gem_object_release_mmap_offset(obj);
 
 	/*

drivers/gpu/drm/i915/gem/i915_gem_stolen.c

@@ -637,13 +637,15 @@ static int __i915_gem_object_create_stolen(struct intel_memory_region *mem,
 	cache_level = HAS_LLC(mem->i915) ? I915_CACHE_LLC : I915_CACHE_NONE;
 	i915_gem_object_set_cache_coherency(obj, cache_level);
 
-	err = i915_gem_object_pin_pages(obj);
-	if (err)
-		return err;
+	if (WARN_ON(!i915_gem_object_trylock(obj)))
+		return -EBUSY;
 
-	i915_gem_object_init_memory_region(obj, mem);
+	err = i915_gem_object_pin_pages(obj);
+	if (!err)
+		i915_gem_object_init_memory_region(obj, mem);
+	i915_gem_object_unlock(obj);
 
-	return 0;
+	return err;
 }
 
 static int _i915_gem_object_stolen_init(struct intel_memory_region *mem,