ecryptfs: get rid of pointless mount references in ecryptfs dentries

->lower_path.mnt has the same value for all dentries on given ecryptfs
instance and if somebody goes for mountpoint-crossing variant where that
would not be true, we can deal with that when it happens (and _not_
with duplicating these reference into each dentry).

As it is, we are better off just sticking a reference into ecryptfs-private
part of superblock and keeping it pinned until ->kill_sb().

That way we can stick a reference to underlying dentry right into ->d_fsdata
of ecryptfs one, getting rid of indirection through struct ecryptfs_dentry_info,
along with the entire struct ecryptfs_dentry_info machinery.

[kudos to Dan Carpenter for spotting a bug in ecryptfs_get_tree() part]

Reviewed-by: Christian Brauner <[e-mail]>
Signed-off-by: Al Viro <[e-mail]>

fs/ecryptfs/dentry.c

···
 	return rc;
 }
 
-struct kmem_cache *ecryptfs_dentry_info_cache;
-
-static void ecryptfs_dentry_free_rcu(struct rcu_head *head)
-{
-	kmem_cache_free(ecryptfs_dentry_info_cache,
-		container_of(head, struct ecryptfs_dentry_info, rcu));
-}
-
 /**
  * ecryptfs_d_release
  * @dentry: The ecryptfs dentry
···
  */
 static void ecryptfs_d_release(struct dentry *dentry)
 {
-	struct ecryptfs_dentry_info *p = dentry->d_fsdata;
-	if (p) {
-		path_put(&p->lower_path);
-		call_rcu(&p->rcu, ecryptfs_dentry_free_rcu);
-	}
+	dput(dentry->d_fsdata);
 }
 
 const struct dentry_operations ecryptfs_dops = {

fs/ecryptfs/ecryptfs_kernel.h

···
 	struct ecryptfs_crypt_stat crypt_stat;
 };
 
-/* dentry private data. Each dentry must keep track of a lower
- * vfsmount too. */
-struct ecryptfs_dentry_info {
-	struct path lower_path;
-	struct rcu_head rcu;
-};
-
 /**
  * ecryptfs_global_auth_tok - A key used to encrypt all new files under the mountpoint
  * @flags: Status flags
···
 /* superblock private data. */
 struct ecryptfs_sb_info {
 	struct super_block *wsi_sb;
+	struct vfsmount *lower_mnt;
 	struct ecryptfs_mount_crypt_stat mount_crypt_stat;
 };
 
···
 }
 
 static inline void
-ecryptfs_set_dentry_private(struct dentry *dentry,
-			    struct ecryptfs_dentry_info *dentry_info)
+ecryptfs_set_dentry_lower(struct dentry *dentry,
+			  struct dentry *lower_dentry)
 {
-	dentry->d_fsdata = dentry_info;
+	dentry->d_fsdata = lower_dentry;
 }
 
 static inline struct dentry *
 ecryptfs_dentry_to_lower(struct dentry *dentry)
 {
-	return ((struct ecryptfs_dentry_info *)dentry->d_fsdata)->lower_path.dentry;
+	return dentry->d_fsdata;
 }
 
-static inline const struct path *
-ecryptfs_dentry_to_lower_path(struct dentry *dentry)
+static inline struct path
+ecryptfs_lower_path(struct dentry *dentry)
 {
-	return &((struct ecryptfs_dentry_info *)dentry->d_fsdata)->lower_path;
+	return (struct path){
+		.mnt = ecryptfs_superblock_to_private(dentry->d_sb)->lower_mnt,
+		.dentry = ecryptfs_dentry_to_lower(dentry)
+	};
 }
 
 #define ecryptfs_printk(type, fmt, arg...) \
···
 
 extern struct kmem_cache *ecryptfs_auth_tok_list_item_cache;
 extern struct kmem_cache *ecryptfs_file_info_cache;
-extern struct kmem_cache *ecryptfs_dentry_info_cache;
 extern struct kmem_cache *ecryptfs_inode_info_cache;
 extern struct kmem_cache *ecryptfs_sb_info_cache;
 extern struct kmem_cache *ecryptfs_header_cache;
···
 	size_t *encoded_name_size,
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat,
 	const char *name, size_t name_size);
-struct dentry *ecryptfs_lower_dentry(struct dentry *this_dentry);
 void ecryptfs_dump_hex(char *data, int bytes);
 int virt_to_scatterlist(const void *addr, int size, struct scatterlist *sg,
 			int sg_size);

fs/ecryptfs/file.c

···
 				struct iov_iter *to)
 {
 	ssize_t rc;
-	const struct path *path;
 	struct file *file = iocb->ki_filp;
 
 	rc = generic_file_read_iter(iocb, to);
 	if (rc >= 0) {
-		path = ecryptfs_dentry_to_lower_path(file->f_path.dentry);
-		touch_atime(path);
+		struct path path = ecryptfs_lower_path(file->f_path.dentry);
+		touch_atime(&path);
 	}
 	return rc;
 }
···
 						 size_t len, unsigned int flags)
 {
 	ssize_t rc;
-	const struct path *path;
 
 	rc = filemap_splice_read(in, ppos, pipe, len, flags);
 	if (rc >= 0) {
-		path = ecryptfs_dentry_to_lower_path(in->f_path.dentry);
-		touch_atime(path);
+		struct path path = ecryptfs_lower_path(in->f_path.dentry);
+		touch_atime(&path);
 	}
 	return rc;
 }
···
 	 * ecryptfs_lookup() */
 	struct ecryptfs_file_info *file_info;
 	struct file *lower_file;
+	struct path path;
 
 	/* Released in ecryptfs_release or end of function if failure */
 	file_info = kmem_cache_zalloc(ecryptfs_file_info_cache, GFP_KERNEL);
···
 				"Error attempting to allocate memory\n");
 		return -ENOMEM;
 	}
-	lower_file = dentry_open(ecryptfs_dentry_to_lower_path(ecryptfs_dentry),
-				 file->f_flags, current_cred());
+	path = ecryptfs_lower_path(ecryptfs_dentry);
+	lower_file = dentry_open(&path, file->f_flags, current_cred());
 	if (IS_ERR(lower_file)) {
 		printk(KERN_ERR "%s: Error attempting to initialize "
 			"the lower file for the dentry with name "

fs/ecryptfs/inode.c

···
 static struct dentry *ecryptfs_lookup_interpose(struct dentry *dentry,
 				     struct dentry *lower_dentry)
 {
-	const struct path *path = ecryptfs_dentry_to_lower_path(dentry->d_parent);
+	struct dentry *lower_parent = ecryptfs_dentry_to_lower(dentry->d_parent);
 	struct inode *inode, *lower_inode;
-	struct ecryptfs_dentry_info *dentry_info;
 	int rc = 0;
 
-	dentry_info = kmem_cache_alloc(ecryptfs_dentry_info_cache, GFP_KERNEL);
-	if (!dentry_info) {
-		dput(lower_dentry);
-		return ERR_PTR(-ENOMEM);
-	}
-
 	fsstack_copy_attr_atime(d_inode(dentry->d_parent),
-				d_inode(path->dentry));
+				d_inode(lower_parent));
 	BUG_ON(!d_count(lower_dentry));
 
-	ecryptfs_set_dentry_private(dentry, dentry_info);
-	dentry_info->lower_path.mnt = mntget(path->mnt);
-	dentry_info->lower_path.dentry = lower_dentry;
+	ecryptfs_set_dentry_lower(dentry, lower_dentry);
 
 	/*
 	 * negative dentry can go positive under us here - its parent is not
···
 {
 	struct dentry *dentry = path->dentry;
 	struct kstat lower_stat;
+	struct path lower_path = ecryptfs_lower_path(dentry);
 	int rc;
 
-	rc = vfs_getattr_nosec(ecryptfs_dentry_to_lower_path(dentry),
-			       &lower_stat, request_mask, flags);
+	rc = vfs_getattr_nosec(&lower_path, &lower_stat, request_mask, flags);
 	if (!rc) {
 		fsstack_copy_attr_all(d_inode(dentry),
 				      ecryptfs_inode_to_lower(d_inode(dentry)));

fs/ecryptfs/main.c

···
 				    struct file **lower_file)
 {
 	const struct cred *cred = current_cred();
-	const struct path *path = ecryptfs_dentry_to_lower_path(dentry);
+	struct path path = ecryptfs_lower_path(dentry);
 	int rc;
 
-	rc = ecryptfs_privileged_open(lower_file, path->dentry, path->mnt,
-				      cred);
+	rc = ecryptfs_privileged_open(lower_file, path.dentry, path.mnt, cred);
 	if (rc) {
 		printk(KERN_ERR "Error opening lower file "
 		       "for lower_dentry [0x%p] and lower_mnt [0x%p]; "
-		       "rc = [%d]\n", path->dentry, path->mnt, rc);
+		       "rc = [%d]\n", path.dentry, path.mnt, rc);
 		(*lower_file) = NULL;
 	}
 	return rc;
···
 	struct ecryptfs_fs_context *ctx = fc->fs_private;
 	struct ecryptfs_sb_info *sbi = fc->s_fs_info;
 	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
-	struct ecryptfs_dentry_info *root_info;
 	const char *err = "Getting sb failed";
 	struct inode *inode;
 	struct path path;
···
 		goto out_free;
 	}
 
-	rc = -ENOMEM;
-	root_info = kmem_cache_zalloc(ecryptfs_dentry_info_cache, GFP_KERNEL);
-	if (!root_info)
-		goto out_free;
-
-	/* ->kill_sb() will take care of root_info */
-	ecryptfs_set_dentry_private(s->s_root, root_info);
-	root_info->lower_path = path;
+	ecryptfs_set_dentry_lower(s->s_root, path.dentry);
+	ecryptfs_superblock_to_private(s)->lower_mnt = path.mnt;
 
 	s->s_flags |= SB_ACTIVE;
 	fc->root = dget(s->s_root);
···
 	kill_anon_super(sb);
 	if (!sb_info)
 		return;
+	mntput(sb_info->lower_mnt);
 	ecryptfs_destroy_mount_crypt_stat(&sb_info->mount_crypt_stat);
 	kmem_cache_free(ecryptfs_sb_info_cache, sb_info);
 }
···
 		.cache = &ecryptfs_file_info_cache,
 		.name = "ecryptfs_file_cache",
 		.size = sizeof(struct ecryptfs_file_info),
-	},
-	{
-		.cache = &ecryptfs_dentry_info_cache,
-		.name = "ecryptfs_dentry_info_cache",
-		.size = sizeof(struct ecryptfs_dentry_info),
 	},
 	{
 		.cache = &ecryptfs_inode_info_cache,