mm/swapfile: fix broken kabi in swap_info_struct

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I645JI

-------------------------------

This patch fix kabi problem introduced by commit
("mm/swapfile:use percpu_ref to serialize against concurrent swapoff").

Considering swap_info_struct is referenced by pointer and dont use
in third module, so use KABI_EXTEND for two new member variables in
swap_info_struct. Besides, dont remove unused enum value SWP_VALID,
avoid unnecessary undefined alarms.
Signed-off-by: NChen Wandun <chenwandun@huawei.com>
Reviewed-by: Kefeng Wang<wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

include/linux/swap.h

@@ -187,6 +187,7 @@ enum {
 	SWP_PAGE_DISCARD = (1 << 10),	/* freed swap page-cluster discards */
 	SWP_STABLE_WRITES = (1 << 11),	/* no overwrite PG_writeback pages */
 	SWP_SYNCHRONOUS_IO = (1 << 12),	/* synchronous IO is efficient */
+	SWP_VALID	= (1 << 13),	/* swap is valid to be operated on? */
 					/* add others here before... */
 	SWP_SCANNING	= (1 << 14),	/* refcount in scan_swap_map */
 };
@@ -249,7 +250,6 @@ struct swap_cluster_list {
  * The in-memory structure used to track swap areas.
  */
 struct swap_info_struct {
-	struct percpu_ref users;	/* indicate and keep swap device valid. */
 	unsigned long	flags;		/* SWP_USED etc: see above */
 	signed short	prio;		/* swap priority of this type */
 	struct plist_node list;		/* entry in swap_active_head */
@@ -270,7 +270,6 @@ struct swap_info_struct {
 	struct block_device *bdev;	/* swap device or bdev of swap file */
 	struct file *swap_file;		/* seldom referenced */
 	unsigned int old_block_size;	/* seldom referenced */
-	struct completion comp;		/* seldom referenced */
 #ifdef CONFIG_FRONTSWAP
 	unsigned long *frontswap_map;	/* frontswap in-use, one bit per page */
 	atomic_t frontswap_pages;	/* frontswap pages in-use counter */
@@ -296,6 +295,8 @@ struct swap_info_struct {
 	struct swap_cluster_list discard_clusters; /* discard clusters list */
 	KABI_RESERVE(1)
 	KABI_RESERVE(2)
+	KABI_EXTEND(struct percpu_ref users)	/* indicate and keep swap device valid. */
+	KABI_EXTEND(struct completion comp)	/* seldom referenced */
 	struct plist_node avail_lists[]; /*
 					   * entries in swap_avail_heads, one
 					   * entry per node.