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Commit b3e76af8 authored by Louis Rilling's avatar Louis Rilling Committed by Mark Fasheh
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configfs: Fix deadlock with racing rmdir() and rename() 



This patch fixes the deadlock between racing sys_rename() and configfs_rmdir().

The idea is to avoid locking i_mutexes of default groups in
configfs_detach_prep(), and rely instead on the new configfs_dirent_lock to
protect against configfs_dirent's linkage mutations. To ensure that an mkdir()
racing with rmdir() will not create new items in a to-be-removed default group,
we make configfs_new_dirent() check for the CONFIGFS_USET_DROPPING flag right
before linking the new dirent, and return error if the flag is set. This makes
racing mkdir()/symlink()/dir_open() fail in places where errors could already
happen, resp. in (attach_item()|attach_group())/create_link()/new_dirent().

configfs_depend() remains safe since it locks all the path from configfs root,
and is thus mutually exclusive with rmdir().

An advantage of this is that now detach_groups() unconditionnaly takes the
default groups i_mutex, which makes it more consistent with populate_groups().

Signed-off-by: default avatarLouis Rilling <Louis.Rilling@kerlabs.com>
Signed-off-by: default avatarJoel Becker <joel.becker@oracle.com>
parent 107ed40b

fs/configfs/dir.c

+25 −20
Original line number Diff line number Diff line
@@ -43,6 +43,10 @@ DECLARE_RWSEM(configfs_rename_sem); 
 * and configfs_dirent_lock locked, in that order.

 * This allows one to safely traverse configfs_dirent trees and symlinks without

 * having to lock inodes.

 *

 * Protects setting of CONFIGFS_USET_DROPPING: checking the flag

 * unlocked is not reliable unless in detach_groups() called from

 * rmdir()/unregister() and from configfs_attach_group()

 */

DEFINE_SPINLOCK(configfs_dirent_lock);
@@ -91,6 +95,11 @@ static struct configfs_dirent *configfs_new_dirent(struct configfs_dirent * pare 
	INIT_LIST_HEAD(&sd->s_children);

	sd->s_element = element;

	spin_lock(&configfs_dirent_lock);

	if (parent_sd->s_type & CONFIGFS_USET_DROPPING) {

		spin_unlock(&configfs_dirent_lock);

		kmem_cache_free(configfs_dir_cachep, sd);

		return ERR_PTR(-ENOENT);

	}

	list_add(&sd->s_sibling, &parent_sd->s_children);

	spin_unlock(&configfs_dirent_lock);
@@ -349,11 +358,11 @@ static struct dentry * configfs_lookup(struct inode *dir, 


/*

 * Only subdirectories count here.  Files (CONFIGFS_NOT_PINNED) are

 * attributes and are removed by rmdir().  We recurse, taking i_mutex

 * on all children that are candidates for default detach.  If the

 * result is clean, then configfs_detach_group() will handle dropping

 * i_mutex.  If there is an error, the caller will clean up the i_mutex

 * holders via configfs_detach_rollback().

 * attributes and are removed by rmdir().  We recurse, setting

 * CONFIGFS_USET_DROPPING on all children that are candidates for

 * default detach.

 * If there is an error, the caller will reset the flags via

 * configfs_detach_rollback().

 */

static int configfs_detach_prep(struct dentry *dentry)

{
@@ -370,8 +379,7 @@ static int configfs_detach_prep(struct dentry *dentry) 
		if (sd->s_type & CONFIGFS_NOT_PINNED)

			continue;

		if (sd->s_type & CONFIGFS_USET_DEFAULT) {

			mutex_lock(&sd->s_dentry->d_inode->i_mutex);

			/* Mark that we've taken i_mutex */

			/* Mark that we're trying to drop the group */

			sd->s_type |= CONFIGFS_USET_DROPPING;



			/*
@@ -392,7 +400,7 @@ out: 
}



/*

 * Walk the tree, dropping i_mutex wherever CONFIGFS_USET_DROPPING is

 * Walk the tree, resetting CONFIGFS_USET_DROPPING wherever it was

 * set.

 */

static void configfs_detach_rollback(struct dentry *dentry)
@@ -403,11 +411,7 @@ static void configfs_detach_rollback(struct dentry *dentry) 
	list_for_each_entry(sd, &parent_sd->s_children, s_sibling) {

		if (sd->s_type & CONFIGFS_USET_DEFAULT) {

			configfs_detach_rollback(sd->s_dentry);



			if (sd->s_type & CONFIGFS_USET_DROPPING) {

			sd->s_type &= ~CONFIGFS_USET_DROPPING;

				mutex_unlock(&sd->s_dentry->d_inode->i_mutex);

			}

		}

	}

}
@@ -486,15 +490,11 @@ static void detach_groups(struct config_group *group) 


		child = sd->s_dentry;



		mutex_lock(&child->d_inode->i_mutex);



		configfs_detach_group(sd->s_element);

		child->d_inode->i_flags |= S_DEAD;



		/*

		 * From rmdir/unregister, a configfs_detach_prep() pass

		 * has taken our i_mutex for us.  Drop it.

		 * From mkdir/register cleanup, there is no sem held.

		 */

		if (sd->s_type & CONFIGFS_USET_DROPPING)

		mutex_unlock(&child->d_inode->i_mutex);



		d_delete(child);
@@ -1181,12 +1181,15 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) 
		return -EINVAL;

	}



	spin_lock(&configfs_dirent_lock);

	ret = configfs_detach_prep(dentry);

	if (ret) {

		configfs_detach_rollback(dentry);

		spin_unlock(&configfs_dirent_lock);

		config_item_put(parent_item);

		return ret;

	}

	spin_unlock(&configfs_dirent_lock);



	/* Get a working ref for the duration of this function */

	item = configfs_get_config_item(dentry);
@@ -1476,9 +1479,11 @@ void configfs_unregister_subsystem(struct configfs_subsystem *subsys) 
	mutex_lock_nested(&configfs_sb->s_root->d_inode->i_mutex,

			  I_MUTEX_PARENT);

	mutex_lock_nested(&dentry->d_inode->i_mutex, I_MUTEX_CHILD);

	spin_lock(&configfs_dirent_lock);

	if (configfs_detach_prep(dentry)) {

		printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n");

	}

	spin_unlock(&configfs_dirent_lock);

	configfs_detach_group(&group->cg_item);

	dentry->d_inode->i_flags |= S_DEAD;

	mutex_unlock(&dentry->d_inode->i_mutex);