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: Louis Rilling <Louis.Rilling@kerlabs.com>
---
fs/configfs/dir.c | 44 ++++++++++++++++++++++++--------------------
1 file changed, 24 insertions(+), 20 deletions(-)
Index: b/fs/configfs/dir.c
===================================================================
--- a/fs/configfs/dir.c 2008-06-12 13:45:18.000000000 +0200
+++ b/fs/configfs/dir.c 2008-06-12 13:50:10.000000000 +0200
@@ -38,6 +38,9 @@
DECLARE_RWSEM(configfs_rename_sem);
/*
* Protects configfs_dirent traversals against linkage mutations
+ * 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
* Can be used as an alternative to taking the concerned i_mutex
*/
DEFINE_SPINLOCK(configfs_dirent_lock);
@@ -86,6 +89,11 @@ static struct configfs_dirent *configfs_
INIT_LIST_HEAD(&sd->s_links);
INIT_LIST_HEAD(&sd->s_children);
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);
sd->s_element = element;
@@ -345,11 +353,11 @@ static struct dentry * configfs_lookup(s
/*
* 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)
{
@@ -366,8 +374,7 @@ static int configfs_detach_prep(struct d
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;
/*
@@ -388,7 +395,7 @@ 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)
@@ -399,11 +406,7 @@ static void configfs_detach_rollback(str
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);
- }
+ sd->s_type &= ~CONFIGFS_USET_DROPPING;
}
}
}
@@ -482,16 +485,12 @@ static void detach_groups(struct config_
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);
+ mutex_unlock(&child->d_inode->i_mutex);
d_delete(child);
dput(child);
@@ -1177,12 +1176,15 @@ static int configfs_rmdir(struct inode *
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);
@@ -1474,9 +1476,11 @@ void configfs_unregister_subsystem(struc
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);
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
--
