f2fs: make f2fs_read_inline_data() more readable

In f2fs_read_inline_data(), it is confused with checking of
inline_data flag, as we checked it before calling. So this
patch add some comments for f2fs_has_inline_data().

Signed-off-by: Chao Liu <liuchao@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -3167,6 +3167,10 @@ static inline int inline_xattr_size(struct inode *inode)
 	return 0;
 }
 
+/*
+ * Notice: check inline_data flag without inode page lock is unsafe.
+ * It could change at any time by f2fs_convert_inline_page().
+ */
 static inline int f2fs_has_inline_data(struct inode *inode)
 {
 	return is_inode_flag_set(inode, FI_INLINE_DATA);