f2fs: avoid to read inline data except first page

Here is a case which could read inline page data not from first page.

1. write inline data
2. lseek to offset 4096
3. read 4096 bytes from offset 4096
	(read_inline_data read inline data page to non-first page,
	And previously VFS has add this page to page cache)
4. ftruncate offset 8192
5. read 4096 bytes from offset 4096
	(we meet this updated page with inline data in cache)

So we should leave this page with inited data and uptodate flag
for this case.

Change log from v1:
 o fix a deadlock bug
Signed-off-by: Chao Yu <chao2.yu@samsung.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>

fs/f2fs/inline.c

@@ -39,6 +39,11 @@ int f2fs_read_inline_data(struct inode *inode, struct page *page)
 	struct page *ipage;
 	void *src_addr, *dst_addr;
 
+	if (page->index) {
+		zero_user_segment(page, 0, PAGE_CACHE_SIZE);
+		goto out;
+	}
+
 	ipage = get_node_page(sbi, inode->i_ino);
 	if (IS_ERR(ipage))
 		return PTR_ERR(ipage);
@@ -52,6 +57,7 @@ int f2fs_read_inline_data(struct inode *inode, struct page *page)
 	kunmap(page);
 	f2fs_put_page(ipage, 1);
 
+out:
 	SetPageUptodate(page);
 	unlock_page(page);