drm/vmwgfx: Fix false lockdep warning

A lockdep warning is hit when evicting surfaces and reserving the backup
buffer. Since this buffer can only be reserved by the process holding the
surface reservation or by the buffer eviction processes that use tryreserve,
there is no real deadlock here, but there's no other way to silence lockdep
than to use a tryreserve. This means the reservation might fail if the buffer
is about to be evicted or swapped out, but we now have code in place to
handle that reasonably well.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrantz <jakob@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -994,7 +994,6 @@ void vmw_resource_unreserve(struct vmw_resource *res,
  */
 static int
 vmw_resource_check_buffer(struct vmw_resource *res,
-			  struct ww_acquire_ctx *ticket,
 			  bool interruptible,
 			  struct ttm_validate_buffer *val_buf)
 {
@@ -1011,7 +1010,7 @@ vmw_resource_check_buffer(struct vmw_resource *res,
 	INIT_LIST_HEAD(&val_list);
 	val_buf->bo = ttm_bo_reference(&res->backup->base);
 	list_add_tail(&val_buf->head, &val_list);
-	ret = ttm_eu_reserve_buffers(ticket, &val_list);
+	ret = ttm_eu_reserve_buffers(NULL, &val_list);
 	if (unlikely(ret != 0))
 		goto out_no_reserve;
 
@@ -1029,7 +1028,7 @@ vmw_resource_check_buffer(struct vmw_resource *res,
 	return 0;
 
 out_no_validate:
-	ttm_eu_backoff_reservation(ticket, &val_list);
+	ttm_eu_backoff_reservation(NULL, &val_list);
 out_no_reserve:
 	ttm_bo_unref(&val_buf->bo);
 	if (backup_dirty)
@@ -1074,8 +1073,7 @@ int vmw_resource_reserve(struct vmw_resource *res, bool no_backup)
  * @val_buf:        Backup buffer information.
  */
 static void
-vmw_resource_backoff_reservation(struct ww_acquire_ctx *ticket,
-				 struct ttm_validate_buffer *val_buf)
+vmw_resource_backoff_reservation(struct ttm_validate_buffer *val_buf)
 {
 	struct list_head val_list;
 
@@ -1084,7 +1082,7 @@ vmw_resource_backoff_reservation(struct ww_acquire_ctx *ticket,
 
 	INIT_LIST_HEAD(&val_list);
 	list_add_tail(&val_buf->head, &val_list);
-	ttm_eu_backoff_reservation(ticket, &val_list);
+	ttm_eu_backoff_reservation(NULL, &val_list);
 	ttm_bo_unref(&val_buf->bo);
 }
 
@@ -1099,14 +1097,12 @@ int vmw_resource_do_evict(struct vmw_resource *res, bool interruptible)
 {
 	struct ttm_validate_buffer val_buf;
 	const struct vmw_res_func *func = res->func;
-	struct ww_acquire_ctx ticket;
 	int ret;
 
 	BUG_ON(!func->may_evict);
 
 	val_buf.bo = NULL;
-	ret = vmw_resource_check_buffer(res, &ticket, interruptible,
-					&val_buf);
+	ret = vmw_resource_check_buffer(res, interruptible, &val_buf);
 	if (unlikely(ret != 0))
 		return ret;
 
@@ -1121,7 +1117,7 @@ int vmw_resource_do_evict(struct vmw_resource *res, bool interruptible)
 	res->backup_dirty = true;
 	res->res_dirty = false;
 out_no_unbind:
-	vmw_resource_backoff_reservation(&ticket, &val_buf);
+	vmw_resource_backoff_reservation(&val_buf);
 
 	return ret;
 }