ovl: store real inode pointer in ->i_private

To get from overlay inode to real inode we currently use 'struct
ovl_entry', which has lifetime connected to overlay dentry.  This is okay,
since each overlay dentry had a new overlay inode allocated.

Following patch will break that assumption, so need to leave out ovl_entry.
This patch stores the real inode directly in i_private, with the lowest bit
used to indicate whether the inode is upper or lower.

Lifetime rules remain, using ovl_inode_real() must only be done while
caller holds ref on overlay dentry (and hence on real dentry), or within
RCU protected regions.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/overlayfs/copy_up.c

@@ -292,6 +292,7 @@ static int ovl_copy_up_locked(struct dentry *workdir, struct dentry *upperdir,
 		goto out_cleanup;
 
 	ovl_dentry_update(dentry, newdentry);
+	ovl_inode_update(d_inode(dentry), d_inode(newdentry));
 	newdentry = NULL;
 
 	/*

fs/overlayfs/dir.c

@@ -167,6 +167,7 @@ static void ovl_instantiate(struct dentry *dentry, struct inode *inode,
 {
 	ovl_dentry_version_inc(dentry->d_parent);
 	ovl_dentry_update(dentry, newdentry);
+	ovl_inode_update(inode, d_inode(newdentry));
 	ovl_copyattr(newdentry->d_inode, inode);
 	d_instantiate(dentry, inode);
 }
@@ -416,7 +417,7 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
 	};
 
 	err = -ENOMEM;
-	inode = ovl_new_inode(dentry->d_sb, mode, dentry->d_fsdata);
+	inode = ovl_new_inode(dentry->d_sb, mode);
 	if (!inode)
 		goto out;
 

fs/overlayfs/inode.c

@@ -117,15 +117,12 @@ static int ovl_getattr(struct vfsmount *mnt, struct dentry *dentry,
 
 int ovl_permission(struct inode *inode, int mask)
 {
-	struct ovl_entry *oe = inode->i_private;
 	bool is_upper;
-	struct dentry *realdentry = ovl_entry_real(oe, &is_upper);
-	struct inode *realinode;
+	struct inode *realinode = ovl_inode_real(inode, &is_upper);
 	const struct cred *old_cred;
 	int err;
 
 	/* Careful in RCU walk mode */
-	realinode = d_inode_rcu(realdentry);
 	if (!realinode) {
 		WARN_ON(!(mask & MAY_NOT_BLOCK));
 		return -ECHILD;
@@ -312,7 +309,7 @@ int ovl_removexattr(struct dentry *dentry, const char *name)
 
 struct posix_acl *ovl_get_acl(struct inode *inode, int type)
 {
-	struct inode *realinode = ovl_inode_real(inode);
+	struct inode *realinode = ovl_inode_real(inode, NULL);
 	const struct cred *old_cred;
 	struct posix_acl *acl;
 
@@ -412,8 +409,7 @@ static const struct inode_operations ovl_symlink_inode_operations = {
 	.update_time	= ovl_update_time,
 };
 
-struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
-			    struct ovl_entry *oe)
+struct inode *ovl_new_inode(struct super_block *sb, umode_t mode)
 {
 	struct inode *inode;
 
@@ -424,7 +420,6 @@ struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
 	inode->i_ino = get_next_ino();
 	inode->i_mode = mode;
 	inode->i_flags |= S_NOCMTIME;
-	inode->i_private = oe;
 
 	mode &= S_IFMT;
 	switch (mode) {

fs/overlayfs/overlayfs.h

@@ -27,6 +27,8 @@ enum ovl_path_type {
 #define OVL_XATTR_PRE_LEN  16
 #define OVL_XATTR_OPAQUE   OVL_XATTR_PRE_NAME"opaque"
 
+#define OVL_ISUPPER_MASK 1UL
+
 static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
 {
 	int err = vfs_rmdir(dir, dentry);
@@ -131,6 +133,16 @@ static inline int ovl_do_whiteout(struct inode *dir, struct dentry *dentry)
 	return err;
 }
 
+static inline struct inode *ovl_inode_real(struct inode *inode, bool *is_upper)
+{
+	unsigned long x = (unsigned long) READ_ONCE(inode->i_private);
+
+	if (is_upper)
+		*is_upper = x & OVL_ISUPPER_MASK;
+
+	return (struct inode *) (x & ~OVL_ISUPPER_MASK);
+}
+
 enum ovl_path_type ovl_path_type(struct dentry *dentry);
 u64 ovl_dentry_version_get(struct dentry *dentry);
 void ovl_dentry_version_inc(struct dentry *dentry);
@@ -141,8 +153,6 @@ int ovl_path_next(int idx, struct dentry *dentry, struct path *path);
 struct dentry *ovl_dentry_upper(struct dentry *dentry);
 struct dentry *ovl_dentry_lower(struct dentry *dentry);
 struct dentry *ovl_dentry_real(struct dentry *dentry);
-struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper);
-struct inode *ovl_inode_real(struct inode *inode);
 struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
 				    bool is_upper);
 struct ovl_dir_cache *ovl_dir_cache(struct dentry *dentry);
@@ -155,6 +165,7 @@ void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
 bool ovl_is_whiteout(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
+void ovl_inode_update(struct inode *inode, struct inode *upperinode);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 			  unsigned int flags);
 struct file *ovl_path_open(struct path *path, int flags);
@@ -183,8 +194,7 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type);
 int ovl_open_maybe_copy_up(struct dentry *dentry, unsigned int file_flags);
 int ovl_update_time(struct inode *inode, struct timespec *ts, int flags);
 
-struct inode *ovl_new_inode(struct super_block *sb, umode_t mode,
-			    struct ovl_entry *oe);
+struct inode *ovl_new_inode(struct super_block *sb, umode_t mode);
 static inline void ovl_copyattr(struct inode *from, struct inode *to)
 {
 	to->i_uid = from->i_uid;

fs/overlayfs/super.c

@@ -145,25 +145,11 @@ struct dentry *ovl_dentry_real(struct dentry *dentry)
 	return realdentry;
 }
 
-struct dentry *ovl_entry_real(struct ovl_entry *oe, bool *is_upper)
+static void ovl_inode_init(struct inode *inode, struct inode *realinode,
+			   bool is_upper)
 {
-	struct dentry *realdentry;
-
-	realdentry = ovl_upperdentry_dereference(oe);
-	if (realdentry) {
-		*is_upper = true;
-	} else {
-		realdentry = __ovl_dentry_lower(oe);
-		*is_upper = false;
-	}
-	return realdentry;
-}
-
-struct inode *ovl_inode_real(struct inode *inode)
-{
-	bool tmp;
-
-	return d_inode(ovl_entry_real(inode->i_private, &tmp));
+	WRITE_ONCE(inode->i_private, (unsigned long) realinode |
+		   (is_upper ? OVL_ISUPPER_MASK : 0));
 }
 
 struct vfsmount *ovl_entry_mnt_real(struct ovl_entry *oe, struct inode *inode,
@@ -235,7 +221,6 @@ void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 
 	WARN_ON(!inode_is_locked(upperdentry->d_parent->d_inode));
 	WARN_ON(oe->__upperdentry);
-	BUG_ON(!upperdentry->d_inode);
 	/*
 	 * Make sure upperdentry is consistent before making it visible to
 	 * ovl_upperdentry_dereference().
@@ -244,6 +229,13 @@ void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
 	oe->__upperdentry = upperdentry;
 }
 
+void ovl_inode_update(struct inode *inode, struct inode *upperinode)
+{
+	WARN_ON(!upperinode);
+	WRITE_ONCE(inode->i_private,
+		   (unsigned long) upperinode | OVL_ISUPPER_MASK);
+}
+
 void ovl_dentry_version_inc(struct dentry *dentry)
 {
 	struct ovl_entry *oe = dentry->d_fsdata;
@@ -574,14 +566,16 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
 
 	if (upperdentry || ctr) {
 		struct dentry *realdentry;
+		struct inode *realinode;
 
 		realdentry = upperdentry ? upperdentry : stack[0].dentry;
+		realinode = d_inode(realdentry);
 
 		err = -ENOMEM;
-		inode = ovl_new_inode(dentry->d_sb, realdentry->d_inode->i_mode,
-				      oe);
+		inode = ovl_new_inode(dentry->d_sb, realinode->i_mode);
 		if (!inode)
 			goto out_free_oe;
+		ovl_inode_init(inode, realinode, !!upperdentry);
 		ovl_copyattr(realdentry->d_inode, inode);
 	}
 
@@ -969,6 +963,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	struct path upperpath = { NULL, NULL };
 	struct path workpath = { NULL, NULL };
 	struct dentry *root_dentry;
+	struct inode *realinode;
 	struct ovl_entry *oe;
 	struct ovl_fs *ufs;
 	struct path *stack = NULL;
@@ -1150,7 +1145,7 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	if (!oe)
 		goto out_put_cred;
 
-	root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
+	root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR));
 	if (!root_dentry)
 		goto out_free_oe;
 
@@ -1169,8 +1164,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 	root_dentry->d_fsdata = oe;
 
-	ovl_copyattr(ovl_dentry_real(root_dentry)->d_inode,
-		     root_dentry->d_inode);
+	realinode = d_inode(ovl_dentry_real(root_dentry));
+	ovl_inode_init(d_inode(root_dentry), realinode, !!upperpath.dentry);
+	ovl_copyattr(realinode, d_inode(root_dentry));
 
 	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
 	sb->s_op = &ovl_super_operations;