Merge tag 'configfs-for-5.4' of git://git.infradead.org/users/hch/configfs

Pull configfs updates from Christoph Hellwig:

- fix a symlink deadlock (Al Viro)

- various cleanups (Al Viro, me)

* tag 'configfs-for-5.4' of git://git.infradead.org/users/hch/configfs:
configfs: calculate the symlink target only once
configfs: make configfs_create() return inode
configfs: factor dirent removal into helpers
configfs: fix a deadlock in configfs_symlink()

fs/configfs/configfs_internal.h

···
 	int			s_dependent_count;
 	struct list_head	s_sibling;
 	struct list_head	s_children;
-	struct list_head	s_links;
+	int			s_links;
 	void			* s_element;
 	int			s_type;
 	umode_t			s_mode;
···
 extern int configfs_is_root(struct config_item *item);
 
 extern struct inode * configfs_new_inode(umode_t mode, struct configfs_dirent *, struct super_block *);
-extern int configfs_create(struct dentry *, umode_t mode, void (*init)(struct inode *));
+extern struct inode *configfs_create(struct dentry *, umode_t mode);
 
 extern int configfs_create_file(struct config_item *, const struct configfs_attribute *);
 extern int configfs_create_bin_file(struct config_item *,
···
 extern struct dentry *configfs_pin_fs(void);
 extern void configfs_release_fs(void);
 
-extern struct rw_semaphore configfs_rename_sem;
 extern const struct file_operations configfs_dir_operations;
 extern const struct file_operations configfs_file_operations;
 extern const struct file_operations configfs_bin_file_operations;
···
 			    const char *symname);
 extern int configfs_unlink(struct inode *dir, struct dentry *dentry);
 
-struct configfs_symlink {
-	struct list_head sl_list;
-	struct config_item *sl_target;
-};
-
-extern int configfs_create_link(struct configfs_symlink *sl,
-				struct dentry *parent,
-				struct dentry *dentry);
+int configfs_create_link(struct configfs_dirent *target, struct dentry *parent,
+		struct dentry *dentry, char *body);
 
 static inline struct config_item * to_item(struct dentry * dentry)
 {
···
 	spin_lock(&dentry->d_lock);
 	if (!d_unhashed(dentry)) {
 		struct configfs_dirent * sd = dentry->d_fsdata;
-		if (sd->s_type & CONFIGFS_ITEM_LINK) {
-			struct configfs_symlink * sl = sd->s_element;
-			item = config_item_get(sl->sl_target);
-		} else
-			item = config_item_get(sd->s_element);
+		item = config_item_get(sd->s_element);
 	}
 	spin_unlock(&dentry->d_lock);
 

fs/configfs/dir.c

···
 #include <linux/configfs.h>
 #include "configfs_internal.h"
 
-DECLARE_RWSEM(configfs_rename_sem);
 /*
  * Protects mutations of configfs_dirent linkage together with proper i_mutex
  * Also protects mutations of symlinks linkage to target configfs_dirent
···
 		return ERR_PTR(-ENOMEM);
 
 	atomic_set(&sd->s_count, 1);
-	INIT_LIST_HEAD(&sd->s_links);
 	INIT_LIST_HEAD(&sd->s_children);
 	sd->s_element = element;
 	sd->s_type = type;
···
 	return 0;
 }
 
-static void init_dir(struct inode * inode)
+static void configfs_remove_dirent(struct dentry *dentry)
 {
-	inode->i_op = &configfs_dir_inode_operations;
-	inode->i_fop = &configfs_dir_operations;
+	struct configfs_dirent *sd = dentry->d_fsdata;
 
-	/* directory inodes start off with i_nlink == 2 (for "." entry) */
-	inc_nlink(inode);
-}
-
-static void configfs_init_file(struct inode * inode)
-{
-	inode->i_size = PAGE_SIZE;
-	inode->i_fop = &configfs_file_operations;
-}
-
-static void configfs_init_bin_file(struct inode *inode)
-{
-	inode->i_size = 0;
-	inode->i_fop = &configfs_bin_file_operations;
-}
-
-static void init_symlink(struct inode * inode)
-{
-	inode->i_op = &configfs_symlink_inode_operations;
+	if (!sd)
+		return;
+	spin_lock(&configfs_dirent_lock);
+	list_del_init(&sd->s_sibling);
+	spin_unlock(&configfs_dirent_lock);
+	configfs_put(sd);
 }
 
 /**
···
 	int error;
 	umode_t mode = S_IFDIR| S_IRWXU | S_IRUGO | S_IXUGO;
 	struct dentry *p = dentry->d_parent;
+	struct inode *inode;
 
 	BUG_ON(!item);
 
···
 		return error;
 
 	configfs_set_dir_dirent_depth(p->d_fsdata, dentry->d_fsdata);
-	error = configfs_create(dentry, mode, init_dir);
-	if (!error) {
-		inc_nlink(d_inode(p));
-		item->ci_dentry = dentry;
-	} else {
-		struct configfs_dirent *sd = dentry->d_fsdata;
-		if (sd) {
-			spin_lock(&configfs_dirent_lock);
-			list_del_init(&sd->s_sibling);
-			spin_unlock(&configfs_dirent_lock);
-			configfs_put(sd);
-		}
-	}
-	return error;
+	inode = configfs_create(dentry, mode);
+	if (IS_ERR(inode))
+		goto out_remove;
+
+	inode->i_op = &configfs_dir_inode_operations;
+	inode->i_fop = &configfs_dir_operations;
+	/* directory inodes start off with i_nlink == 2 (for "." entry) */
+	inc_nlink(inode);
+	d_instantiate(dentry, inode);
+	/* already hashed */
+	dget(dentry);  /* pin directory dentries in core */
+	inc_nlink(d_inode(p));
+	item->ci_dentry = dentry;
+	return 0;
+
+out_remove:
+	configfs_remove_dirent(dentry);
+	return PTR_ERR(inode);
 }
 
 /*
···
 	return ret;
 }
 
-int configfs_create_link(struct configfs_symlink *sl,
-			 struct dentry *parent,
-			 struct dentry *dentry)
+int configfs_create_link(struct configfs_dirent *target, struct dentry *parent,
+		struct dentry *dentry, char *body)
 {
 	int err = 0;
 	umode_t mode = S_IFLNK | S_IRWXUGO;
 	struct configfs_dirent *p = parent->d_fsdata;
+	struct inode *inode;
 
-	err = configfs_make_dirent(p, dentry, sl, mode,
-				   CONFIGFS_ITEM_LINK, p->s_frag);
-	if (!err) {
-		err = configfs_create(dentry, mode, init_symlink);
-		if (err) {
-			struct configfs_dirent *sd = dentry->d_fsdata;
-			if (sd) {
-				spin_lock(&configfs_dirent_lock);
-				list_del_init(&sd->s_sibling);
-				spin_unlock(&configfs_dirent_lock);
-				configfs_put(sd);
-			}
-		}
-	}
-	return err;
+	err = configfs_make_dirent(p, dentry, target, mode, CONFIGFS_ITEM_LINK,
+			p->s_frag);
+	if (err)
+		return err;
+
+	inode = configfs_create(dentry, mode);
+	if (IS_ERR(inode))
+		goto out_remove;
+
+	inode->i_link = body;
+	inode->i_op = &configfs_symlink_inode_operations;
+	d_instantiate(dentry, inode);
+	dget(dentry);  /* pin link dentries in core */
+	return 0;
+
+out_remove:
+	configfs_remove_dirent(dentry);
+	return PTR_ERR(inode);
 }
 
 static void remove_dir(struct dentry * d)
 {
 	struct dentry * parent = dget(d->d_parent);
-	struct configfs_dirent * sd;
 
-	sd = d->d_fsdata;
-	spin_lock(&configfs_dirent_lock);
-	list_del_init(&sd->s_sibling);
-	spin_unlock(&configfs_dirent_lock);
-	configfs_put(sd);
+	configfs_remove_dirent(d);
+
 	if (d_really_is_positive(d))
 		simple_rmdir(d_inode(parent),d);
 
···
 static int configfs_attach_attr(struct configfs_dirent * sd, struct dentry * dentry)
 {
 	struct configfs_attribute * attr = sd->s_element;
-	int error;
+	struct inode *inode;
 
 	spin_lock(&configfs_dirent_lock);
 	dentry->d_fsdata = configfs_get(sd);
 	sd->s_dentry = dentry;
 	spin_unlock(&configfs_dirent_lock);
 
-	error = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG,
-				(sd->s_type & CONFIGFS_ITEM_BIN_ATTR) ?
-					configfs_init_bin_file :
-					configfs_init_file);
-	if (error)
+	inode = configfs_create(dentry, (attr->ca_mode & S_IALLUGO) | S_IFREG);
+	if (IS_ERR(inode)) {
 		configfs_put(sd);
-	return error;
+		return PTR_ERR(inode);
+	}
+	if (sd->s_type & CONFIGFS_ITEM_BIN_ATTR) {
+		inode->i_size = 0;
+		inode->i_fop = &configfs_bin_file_operations;
+	} else {
+		inode->i_size = PAGE_SIZE;
+		inode->i_fop = &configfs_file_operations;
+	}
+	d_add(dentry, inode);
+	return 0;
 }
 
 static struct dentry * configfs_lookup(struct inode *dir,
···
 	parent_sd->s_type |= CONFIGFS_USET_DROPPING;
 
 	ret = -EBUSY;
-	if (!list_empty(&parent_sd->s_links))
+	if (parent_sd->s_links)
 		goto out;
 
 	ret = 0;
···
 	.lookup		= configfs_lookup,
 	.setattr	= configfs_setattr,
 };
-
-#if 0
-int configfs_rename_dir(struct config_item * item, const char *new_name)
-{
-	int error = 0;
-	struct dentry * new_dentry, * parent;
-
-	if (!strcmp(config_item_name(item), new_name))
-		return -EINVAL;
-
-	if (!item->parent)
-		return -EINVAL;
-
-	down_write(&configfs_rename_sem);
-	parent = item->parent->dentry;
-
-	inode_lock(d_inode(parent));
-
-	new_dentry = lookup_one_len(new_name, parent, strlen(new_name));
-	if (!IS_ERR(new_dentry)) {
-		if (d_really_is_negative(new_dentry)) {
-			error = config_item_set_name(item, "%s", new_name);
-			if (!error) {
-				d_add(new_dentry, NULL);
-				d_move(item->dentry, new_dentry);
-			}
-			else
-				d_delete(new_dentry);
-		} else
-			error = -EEXIST;
-		dput(new_dentry);
-	}
-	inode_unlock(d_inode(parent));
-	up_write(&configfs_rename_sem);
-
-	return error;
-}
-#endif
 
 static int configfs_dir_open(struct inode *inode, struct file *file)
 {

fs/configfs/inode.c

···
 
 #endif /* CONFIG_LOCKDEP */
 
-int configfs_create(struct dentry * dentry, umode_t mode, void (*init)(struct inode *))
+struct inode *configfs_create(struct dentry *dentry, umode_t mode)
 {
-	int error = 0;
 	struct inode *inode = NULL;
 	struct configfs_dirent *sd;
 	struct inode *p_inode;
 
 	if (!dentry)
-		return -ENOENT;
+		return ERR_PTR(-ENOENT);
 
 	if (d_really_is_positive(dentry))
-		return -EEXIST;
+		return ERR_PTR(-EEXIST);
 
 	sd = dentry->d_fsdata;
 	inode = configfs_new_inode(mode, sd, dentry->d_sb);
 	if (!inode)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	p_inode = d_inode(dentry->d_parent);
 	p_inode->i_mtime = p_inode->i_ctime = current_time(p_inode);
 	configfs_set_inode_lock_class(sd, inode);
-
-	init(inode);
-	if (S_ISDIR(mode) || S_ISLNK(mode)) {
-		/*
-		 * ->symlink(), ->mkdir(), configfs_register_subsystem() or
-		 * create_default_group() - already hashed.
-		 */
-		d_instantiate(dentry, inode);
-		dget(dentry);  /* pin link and directory dentries in core */
-	} else {
-		/* ->lookup() */
-		d_add(dentry, inode);
-	}
-	return error;
+	return inode;
 }
 
 /*

fs/configfs/mount.c

···
 struct kmem_cache *configfs_dir_cachep;
 static int configfs_mnt_count = 0;
 
+
+static void configfs_free_inode(struct inode *inode)
+{
+	if (S_ISLNK(inode->i_mode))
+		kfree(inode->i_link);
+	free_inode_nonrcu(inode);
+}
+
 static const struct super_operations configfs_ops = {
 	.statfs		= simple_statfs,
 	.drop_inode	= generic_delete_inode,
+	.free_inode	= configfs_free_inode,
 };
 
 static struct config_group configfs_root_group = {

fs/configfs/symlink.c

···
 	}
 }
 
+static int configfs_get_target_path(struct config_item *item,
+		struct config_item *target, char *path)
+{
+	int depth, size;
+	char *s;
+
+	depth = item_depth(item);
+	size = item_path_length(target) + depth * 3 - 1;
+	if (size > PATH_MAX)
+		return -ENAMETOOLONG;
+
+	pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
+
+	for (s = path; depth--; s += 3)
+		strcpy(s,"../");
+
+	fill_item_path(target, path, size);
+	pr_debug("%s: path = '%s'\n", __func__, path);
+	return 0;
+}
+
 static int create_link(struct config_item *parent_item,
 		       struct config_item *item,
 		       struct dentry *dentry)
 {
 	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
-	struct configfs_symlink *sl;
+	char *body;
 	int ret;
 
-	ret = -ENOENT;
 	if (!configfs_dirent_is_ready(target_sd))
-		goto out;
-	ret = -ENOMEM;
-	sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
-	if (sl) {
-		spin_lock(&configfs_dirent_lock);
-		if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
-			spin_unlock(&configfs_dirent_lock);
-			kfree(sl);
-			return -ENOENT;
-		}
-		sl->sl_target = config_item_get(item);
-		list_add(&sl->sl_list, &target_sd->s_links);
-		spin_unlock(&configfs_dirent_lock);
-		ret = configfs_create_link(sl, parent_item->ci_dentry,
-					   dentry);
-		if (ret) {
-			spin_lock(&configfs_dirent_lock);
-			list_del_init(&sl->sl_list);
-			spin_unlock(&configfs_dirent_lock);
-			config_item_put(item);
-			kfree(sl);
-		}
-	}
+		return -ENOENT;
 
-out:
+	body = kzalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!body)
+		return -ENOMEM;
+
+	configfs_get(target_sd);
+	spin_lock(&configfs_dirent_lock);
+	if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
+		spin_unlock(&configfs_dirent_lock);
+		configfs_put(target_sd);
+		kfree(body);
+		return -ENOENT;
+	}
+	target_sd->s_links++;
+	spin_unlock(&configfs_dirent_lock);
+	ret = configfs_get_target_path(item, item, body);
+	if (!ret)
+		ret = configfs_create_link(target_sd, parent_item->ci_dentry,
+					   dentry, body);
+	if (ret) {
+		spin_lock(&configfs_dirent_lock);
+		target_sd->s_links--;
+		spin_unlock(&configfs_dirent_lock);
+		configfs_put(target_sd);
+		kfree(body);
+	}
 	return ret;
 }
 
···
 	 * Fake invisibility if dir belongs to a group/default groups hierarchy
 	 * being attached
 	 */
-	ret = -ENOENT;
 	if (!configfs_dirent_is_ready(sd))
-		goto out;
+		return -ENOENT;
 
 	parent_item = configfs_get_config_item(dentry->d_parent);
 	type = parent_item->ci_type;
···
 	    !type->ct_item_ops->allow_link)
 		goto out_put;
 
+	/*
+	 * This is really sick.  What they wanted was a hybrid of
+	 * link(2) and symlink(2) - they wanted the target resolved
+	 * at syscall time (as link(2) would've done), be a directory
+	 * (which link(2) would've refused to do) *AND* be a deep
+	 * fucking magic, making the target busy from rmdir POV.
+	 * symlink(2) is nothing of that sort, and the locking it
+	 * gets matches the normal symlink(2) semantics.  Without
+	 * attempts to resolve the target (which might very well
+	 * not even exist yet) done prior to locking the parent
+	 * directory.  This perversion, OTOH, needs to resolve
+	 * the target, which would lead to obvious deadlocks if
+	 * attempted with any directories locked.
+	 *
+	 * Unfortunately, that garbage is userland ABI and we should've
+	 * said "no" back in 2005.  Too late now, so we get to
+	 * play very ugly games with locking.
+	 *
+	 * Try *ANYTHING* of that sort in new code, and you will
+	 * really regret it.  Just ask yourself - what could a BOFH
+	 * do to me and do I want to find it out first-hand?
+	 *
+	 *  AV, a thoroughly annoyed bastard.
+	 */
+	inode_unlock(dir);
 	ret = get_target(symname, &path, &target_item, dentry->d_sb);
+	inode_lock(dir);
 	if (ret)
 		goto out_put;
 
-	ret = type->ct_item_ops->allow_link(parent_item, target_item);
+	if (dentry->d_inode || d_unhashed(dentry))
+		ret = -EEXIST;
+	else
+		ret = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+	if (!ret)
+		ret = type->ct_item_ops->allow_link(parent_item, target_item);
 	if (!ret) {
 		mutex_lock(&configfs_symlink_mutex);
 		ret = create_link(parent_item, target_item, dentry);
···
 
 out_put:
 	config_item_put(parent_item);
-
-out:
 	return ret;
 }
 
 int configfs_unlink(struct inode *dir, struct dentry *dentry)
 {
-	struct configfs_dirent *sd = dentry->d_fsdata;
-	struct configfs_symlink *sl;
+	struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
 	struct config_item *parent_item;
 	const struct config_item_type *type;
 	int ret;
···
 	if (!(sd->s_type & CONFIGFS_ITEM_LINK))
 		goto out;
 
-	sl = sd->s_element;
+	target_sd = sd->s_element;
 
 	parent_item = configfs_get_config_item(dentry->d_parent);
 	type = parent_item->ci_type;
···
 
 	/*
 	 * drop_link() must be called before
-	 * list_del_init(&sl->sl_list), so that the order of
+	 * decrementing target's ->s_links, so that the order of
 	 * drop_link(this, target) and drop_item(target) is preserved.
 	 */
 	if (type && type->ct_item_ops &&
 	    type->ct_item_ops->drop_link)
 		type->ct_item_ops->drop_link(parent_item,
-					       sl->sl_target);
+					       target_sd->s_element);
 
 	spin_lock(&configfs_dirent_lock);
-	list_del_init(&sl->sl_list);
+	target_sd->s_links--;
 	spin_unlock(&configfs_dirent_lock);
-
-	/* Put reference from create_link() */
-	config_item_put(sl->sl_target);
-	kfree(sl);
+	configfs_put(target_sd);
 
 	config_item_put(parent_item);
 
···
 	return ret;
 }
 
-static int configfs_get_target_path(struct config_item * item, struct config_item * target,
-				   char *path)
-{
-	char * s;
-	int depth, size;
-
-	depth = item_depth(item);
-	size = item_path_length(target) + depth * 3 - 1;
-	if (size > PATH_MAX)
-		return -ENAMETOOLONG;
-
-	pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
-
-	for (s = path; depth--; s += 3)
-		strcpy(s,"../");
-
-	fill_item_path(target, path, size);
-	pr_debug("%s: path = '%s'\n", __func__, path);
-
-	return 0;
-}
-
-static int configfs_getlink(struct dentry *dentry, char * path)
-{
-	struct config_item *item, *target_item;
-	int error = 0;
-
-	item = configfs_get_config_item(dentry->d_parent);
-	if (!item)
-		return -EINVAL;
-
-	target_item = configfs_get_config_item(dentry);
-	if (!target_item) {
-		config_item_put(item);
-		return -EINVAL;
-	}
-
-	down_read(&configfs_rename_sem);
-	error = configfs_get_target_path(item, target_item, path);
-	up_read(&configfs_rename_sem);
-
-	config_item_put(item);
-	config_item_put(target_item);
-	return error;
-
-}
-
-static const char *configfs_get_link(struct dentry *dentry,
-				     struct inode *inode,
-				     struct delayed_call *done)
-{
-	char *body;
-	int error;
-
-	if (!dentry)
-		return ERR_PTR(-ECHILD);
-
-	body = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!body)
-		return ERR_PTR(-ENOMEM);
-
-	error = configfs_getlink(dentry, body);
-	if (!error) {
-		set_delayed_call(done, kfree_link, body);
-		return body;
-	}
-
-	kfree(body);
-	return ERR_PTR(error);
-}
-
 const struct inode_operations configfs_symlink_inode_operations = {
-	.get_link = configfs_get_link,
+	.get_link = simple_get_link,
 	.setattr = configfs_setattr,
 };