drm/ttm: Use LRU hitches

Have iterators insert themselves into the list they are iterating
over using hitch list nodes. Since only the iterator owner
can remove these list nodes from the list, it's safe to unlock
the list and when continuing, use them as a starting point. Due to
the way LRU bumping works in TTM, newly added items will not be
missed, and bumped items will be iterated over a second time before
reaching the end of the list.

The exception is list with bulk move sublists. When bumping a
sublist, a hitch that is part of that sublist will also be moved
and we might miss items if restarting from it. This will be
addressed in a later patch.

Changes in previous series:
- Updated ttm_resource_cursor_fini() documentation.
v2:
- Don't reorder ttm_resource_manager_first() and _next().
  (Christian König).
- Use list_add instead of list_move
  (Christian König)
v3:
- Split into two patches, one cleanup, one new functionality
  (Christian König)
- use ttm_resource_cursor_fini_locked() instead of open-coding
  (Matthew Brost)

Cc: Christian König <christian.koenig@amd.com>
Cc: Somalapuram Amaranath <Amaranath.Somalapuram@amd.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <dri-devel@lists.freedesktop.org>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240705153206.68526-4-thomas.hellstrom@linux.intel.com
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -621,6 +621,7 @@ int ttm_mem_evict_first(struct ttm_device *bdev,
 		if (locked)
 			dma_resv_unlock(res->bo->base.resv);
 	}
+	ttm_resource_cursor_fini_locked(&cursor);
 
 	if (!bo) {
 		if (busy_bo && !ttm_bo_get_unless_zero(busy_bo))

drivers/gpu/drm/ttm/ttm_device.c

@@ -170,12 +170,17 @@ int ttm_device_swapout(struct ttm_device *bdev, struct ttm_operation_ctx *ctx,
 			num_pages = PFN_UP(bo->base.size);
 			ret = ttm_bo_swapout(bo, ctx, gfp_flags);
 			/* ttm_bo_swapout has dropped the lru_lock */
-			if (!ret)
+			if (!ret) {
+				ttm_resource_cursor_fini(&cursor);
 				return num_pages;
-			if (ret != -EBUSY)
+			}
+			if (ret != -EBUSY) {
+				ttm_resource_cursor_fini(&cursor);
 				return ret;
 			}
 		}
+	}
+	ttm_resource_cursor_fini_locked(&cursor);
 	spin_unlock(&bdev->lru_lock);
 	return 0;
 }

drivers/gpu/drm/ttm/ttm_resource.c

@@ -33,6 +33,37 @@
 
 #include <drm/drm_util.h>
 
+/**
+ * ttm_resource_cursor_fini_locked() - Finalize the LRU list cursor usage
+ * @cursor: The struct ttm_resource_cursor to finalize.
+ *
+ * The function pulls the LRU list cursor off any lists it was previusly
+ * attached to. Needs to be called with the LRU lock held. The function
+ * can be called multiple times after eachother.
+ */
+void ttm_resource_cursor_fini_locked(struct ttm_resource_cursor *cursor)
+{
+	lockdep_assert_held(&cursor->man->bdev->lru_lock);
+	list_del_init(&cursor->hitch.link);
+}
+
+/**
+ * ttm_resource_cursor_fini() - Finalize the LRU list cursor usage
+ * @cursor: The struct ttm_resource_cursor to finalize.
+ *
+ * The function pulls the LRU list cursor off any lists it was previusly
+ * attached to. Needs to be called without the LRU list lock held. The
+ * function can be called multiple times after eachother.
+ */
+void ttm_resource_cursor_fini(struct ttm_resource_cursor *cursor)
+{
+	spinlock_t *lru_lock = &cursor->man->bdev->lru_lock;
+
+	spin_lock(lru_lock);
+	ttm_resource_cursor_fini_locked(cursor);
+	spin_unlock(lru_lock);
+}
+
 /**
  * ttm_lru_bulk_move_init - initialize a bulk move structure
  * @bulk: the structure to init
@@ -485,12 +516,15 @@ void ttm_resource_manager_debug(struct ttm_resource_manager *man,
 EXPORT_SYMBOL(ttm_resource_manager_debug);
 
 /**
- * ttm_resource_manager_first
- *
+ * ttm_resource_manager_first() - Start iterating over the resources
+ * of a resource manager
  * @man: resource manager to iterate over
  * @cursor: cursor to record the position
  *
- * Returns the first resource from the resource manager.
+ * Initializes the cursor and starts iterating. When done iterating,
+ * the caller must explicitly call ttm_resource_cursor_fini().
+ *
+ * Return: The first resource from the resource manager.
  */
 struct ttm_resource *
 ttm_resource_manager_first(struct ttm_resource_manager *man,
@@ -500,13 +534,15 @@ ttm_resource_manager_first(struct ttm_resource_manager *man,
 
 	cursor->priority = 0;
 	cursor->man = man;
-	cursor->cur = &man->lru[cursor->priority];
+	ttm_lru_item_init(&cursor->hitch, TTM_LRU_HITCH);
+	list_add(&cursor->hitch.link, &man->lru[cursor->priority]);
+
 	return ttm_resource_manager_next(cursor);
 }
 
 /**
- * ttm_resource_manager_next
- *
+ * ttm_resource_manager_next() - Continue iterating over the resource manager
+ * resources
  * @cursor: cursor to record the position
  *
  * Return: the next resource from the resource manager.
@@ -520,10 +556,10 @@ ttm_resource_manager_next(struct ttm_resource_cursor *cursor)
 	lockdep_assert_held(&man->bdev->lru_lock);
 
 	for (;;) {
-		lru = list_entry(cursor->cur, typeof(*lru), link);
+		lru = &cursor->hitch;
 		list_for_each_entry_continue(lru, &man->lru[cursor->priority], link) {
 			if (ttm_lru_item_is_res(lru)) {
-				cursor->cur = &lru->link;
+				list_move(&cursor->hitch.link, &lru->link);
 				return ttm_lru_item_to_res(lru);
 			}
 		}
@@ -531,9 +567,11 @@ ttm_resource_manager_next(struct ttm_resource_cursor *cursor)
 		if (++cursor->priority >= TTM_MAX_BO_PRIORITY)
 			break;
 
-		cursor->cur = &man->lru[cursor->priority];
+		list_move(&cursor->hitch.link, &man->lru[cursor->priority]);
 	}
 
+	ttm_resource_cursor_fini_locked(cursor);
+
 	return NULL;
 }
 

include/drm/ttm/ttm_resource.h

@@ -273,17 +273,22 @@ ttm_lru_item_to_res(struct ttm_lru_item *item)
  * struct ttm_resource_cursor
  *
  * @man: The resource manager currently being iterated over.
- * @cur: The list head the cursor currently points to.
+ * @hitch: A hitch list node inserted before the next resource
+ * to iterate over.
  * @priority: the current priority
  *
  * Cursor to iterate over the resources in a manager.
  */
 struct ttm_resource_cursor {
 	struct ttm_resource_manager *man;
-	struct list_head *cur;
+	struct ttm_lru_item hitch;
 	unsigned int priority;
 };
 
+void ttm_resource_cursor_fini_locked(struct ttm_resource_cursor *cursor);
+
+void ttm_resource_cursor_fini(struct ttm_resource_cursor *cursor);
+
 /**
  * struct ttm_lru_bulk_move_pos
  *