overlayfs: convert to ctime accessor functions

In later patches, we're going to change how the inode's ctime field is
used. Switch to using accessor functions instead of raw accesses of
inode->i_ctime.
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230705190309.579783-64-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/overlayfs/file.c

@@ -239,6 +239,7 @@ static loff_t ovl_llseek(struct file *file, loff_t offset, int whence)
 static void ovl_file_accessed(struct file *file)
 {
 	struct inode *inode, *upperinode;
+	struct timespec64 ctime, uctime;
 
 	if (file->f_flags & O_NOATIME)
 		return;
@@ -249,10 +250,12 @@ static void ovl_file_accessed(struct file *file)
 	if (!upperinode)
 		return;
 
+	ctime = inode_get_ctime(inode);
+	uctime = inode_get_ctime(upperinode);
 	if ((!timespec64_equal(&inode->i_mtime, &upperinode->i_mtime) ||
-	     !timespec64_equal(&inode->i_ctime, &upperinode->i_ctime))) {
+	     !timespec64_equal(&ctime, &uctime))) {
 		inode->i_mtime = upperinode->i_mtime;
-		inode->i_ctime = upperinode->i_ctime;
+		inode_set_ctime_to_ts(inode, uctime);
 	}
 
 	touch_atime(&file->f_path);

fs/overlayfs/util.c

@@ -1202,6 +1202,6 @@ void ovl_copyattr(struct inode *inode)
 	inode->i_mode = realinode->i_mode;
 	inode->i_atime = realinode->i_atime;
 	inode->i_mtime = realinode->i_mtime;
-	inode->i_ctime = realinode->i_ctime;
+	inode_set_ctime_to_ts(inode, inode_get_ctime(realinode));
 	i_size_write(inode, i_size_read(realinode));
 }