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>

5 files changed, 40 insertions, 37 deletions

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 80aa6f1eb336..54e5d6681786 100644
--- a/fs/overlayfs/copy_up.c
+++ b/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;
 
         /*
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index b4eac8173f93..96b1bdcf3674 100644
--- a/fs/overlayfs/dir.c
+++ b/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;
 
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index 0598c169ce41..2bdd3cae0f71 100644
--- a/fs/overlayfs/inode.c
+++ b/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 @@ out:
 
 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) {
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index fb73c09a84e7..6410209ea616 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/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;
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 058103c60f54..313f773652ff 100644
--- a/fs/overlayfs/super.c
+++ b/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;