f2fs: fix an error case of missing update inode page

-Thread A                             Thread B

-write_checkpoint
 -block_operations
  -f2fs_unlock_all                    -f2fs_sync_file
                                       -f2fs_write_inode
                                        -f2fs_inode_synced
    -f2fs_sync_inode_meta
     -sync_node_pages
                                        -set_page_drity

In this case, if sudden power off without next new checkpoint,
the last inode page update will lost. wb_writeback is same with
fsync.

Yunlei also reproduced the bug by:

@@ -366,7 +366,7 @@ int update_inode(struct inode *inode, struct page *node_page)
        struct extent_tree *et = F2FS_I(inode)->extent_tree;

        f2fs_inode_synced(inode);
-
+       msleep(10000);
        f2fs_wait_on_page_writeback(node_page, NODE, true);

shell 1:                                       shell2:

dd if=/dev/zero of=./test bs=1M count=10
sync
echo "hello" >> ./test
fsync test  // sleep 10s
                                               sync //return quickly
echo c > /proc/sysrq-trigger
Signed-off-by: NYunlei He <heyunlei@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -2513,8 +2513,8 @@ void f2fs_inode_chksum_set(struct f2fs_sb_info *sbi, struct page *page);
 struct inode *f2fs_iget(struct super_block *sb, unsigned long ino);
 struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino);
 int try_to_free_nats(struct f2fs_sb_info *sbi, int nr_shrink);
-int update_inode(struct inode *inode, struct page *node_page);
-int update_inode_page(struct inode *inode);
+void update_inode(struct inode *inode, struct page *node_page);
+void update_inode_page(struct inode *inode);
 int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc);
 void f2fs_evict_inode(struct inode *inode);
 void handle_failed_inode(struct inode *inode);

fs/f2fs/inode.c

@@ -360,14 +360,15 @@ struct inode *f2fs_iget_retry(struct super_block *sb, unsigned long ino)
 	return inode;
 }
 
-int update_inode(struct inode *inode, struct page *node_page)
+void update_inode(struct inode *inode, struct page *node_page)
 {
 	struct f2fs_inode *ri;
 	struct extent_tree *et = F2FS_I(inode)->extent_tree;
 
-	f2fs_inode_synced(inode);
-
 	f2fs_wait_on_page_writeback(node_page, NODE, true);
+	set_page_dirty(node_page);
+
+	f2fs_inode_synced(inode);
 
 	ri = F2FS_INODE(node_page);
 
@@ -426,14 +427,12 @@ int update_inode(struct inode *inode, struct page *node_page)
 	if (inode->i_nlink == 0)
 		clear_inline_node(node_page);
 
-	return set_page_dirty(node_page);
 }
 
-int update_inode_page(struct inode *inode)
+void update_inode_page(struct inode *inode)
 {
 	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
 	struct page *node_page;
-	int ret = 0;
 retry:
 	node_page = get_node_page(sbi, inode->i_ino);
 	if (IS_ERR(node_page)) {
@@ -444,11 +443,10 @@ int update_inode_page(struct inode *inode)
 		} else if (err != -ENOENT) {
 			f2fs_stop_checkpoint(sbi, false);
 		}
-		return 0;
+		return;
 	}
-	ret = update_inode(inode, node_page);
+	update_inode(inode, node_page);
 	f2fs_put_page(node_page, 1);
-	return ret;
 }
 
 int f2fs_write_inode(struct inode *inode, struct writeback_control *wbc)