ovl: fix relatime for directories

Need to treat non-regular overlayfs files the same as regular files when
checking for an atime update.

Add a d_real() flag to make it return the upper dentry for all file types.
Reported-by: "zhangyi (F)" <yi.zhang@huawei.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/inode.c

@@ -1569,11 +1569,24 @@ EXPORT_SYMBOL(bmap);
 static void update_ovl_inode_times(struct dentry *dentry, struct inode *inode,
 			       bool rcu)
 {
-	if (!rcu) {
-		struct inode *realinode = d_real_inode(dentry);
+	struct dentry *upperdentry;
 
-		if (unlikely(inode != realinode) &&
-		    (!timespec_equal(&inode->i_mtime, &realinode->i_mtime) ||
+	/*
+	 * Nothing to do if in rcu or if non-overlayfs
+	 */
+	if (rcu || likely(!(dentry->d_flags & DCACHE_OP_REAL)))
+		return;
+
+	upperdentry = d_real(dentry, NULL, 0, D_REAL_UPPER);
+
+	/*
+	 * If file is on lower then we can't update atime, so no worries about
+	 * stale mtime/ctime.
+	 */
+	if (upperdentry) {
+		struct inode *realinode = d_inode(upperdentry);
+
+		if ((!timespec_equal(&inode->i_mtime, &realinode->i_mtime) ||
 		     !timespec_equal(&inode->i_ctime, &realinode->i_ctime))) {
 			inode->i_mtime = realinode->i_mtime;
 			inode->i_ctime = realinode->i_ctime;

fs/overlayfs/super.c

@@ -75,6 +75,9 @@ static struct dentry *ovl_d_real(struct dentry *dentry,
 	struct dentry *real;
 	int err;
 
+	if (flags & D_REAL_UPPER)
+		return ovl_dentry_upper(dentry);
+
 	if (!d_is_reg(dentry)) {
 		if (!inode || inode == d_inode(dentry))
 			return dentry;

include/linux/dcache.h

@@ -562,6 +562,9 @@ static inline struct dentry *d_backing_dentry(struct dentry *upper)
 	return upper;
 }
 
+/* d_real() flags */
+#define D_REAL_UPPER	0x2	/* return upper dentry or NULL if non-upper */
+
 /**
  * d_real - Return the real dentry
  * @dentry: the dentry to query