From 9a73d78cda750f12e25eb811878f2d9dbab1bc6e Mon Sep 17 00:00:00 2001 From: Louis Rilling Date: Fri, 20 Jun 2008 14:09:22 +0200 Subject: [PATCH] configfs: Fix failing symlink() making rmdir() fail On a similar pattern as mkdir() vs rmdir(), a failing symlink() may make rmdir() fail for the symlink's parent and the symlink's target as well. failing symlink() making target's rmdir() fail: process 1: process 2: symlink("A/S" -> "B") allow_link() create_link() attach to "B" links list rmdir("B") detach_prep("B") error because of new link configfs_create_link("A", "S") error (eg -ENOMEM) failing symlink() making parent's rmdir() fail: process 1: process 2: symlink("A/D/S" -> "B") allow_link() create_link() attach to "B" links list configfs_create_link("A/D", "S") make_dirent("A/D", "S") rmdir("A") detach_prep("A") detach_prep("A/D") error because of "S" create("S") error (eg -ENOMEM) We cannot use the same solution as for mkdir() vs rmdir(), since rmdir() on the target cannot wait on the i_mutex of the new symlink's parent without risking a deadlock (with other symlink() or sys_rename()). Instead we define a global mutex protecting all configfs symlinks attachment, so that rmdir() can avoid the races above. Signed-off-by: Louis Rilling Signed-off-by: Joel Becker Signed-off-by: Mark Fasheh --- fs/configfs/configfs_internal.h | 1 + fs/configfs/dir.c | 10 ++++++++++ fs/configfs/symlink.c | 5 +++++ 3 files changed, 16 insertions(+) (limited to 'fs/configfs') diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h index da015c12e3ea..5f61b26eba9e 100644 --- a/fs/configfs/configfs_internal.h +++ b/fs/configfs/configfs_internal.h @@ -51,6 +51,7 @@ struct configfs_dirent { #define CONFIGFS_USET_IN_MKDIR 0x0200 #define CONFIGFS_NOT_PINNED (CONFIGFS_ITEM_ATTR) +extern struct mutex configfs_symlink_mutex; extern spinlock_t configfs_dirent_lock; extern struct vfsmount * configfs_mount; diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c index cb5ea44846af..4e228c80fe9f 100644 --- a/fs/configfs/dir.c +++ b/fs/configfs/dir.c @@ -1207,6 +1207,11 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) return -EINVAL; } + /* + * Ensure that no racing symlink() will make detach_prep() fail while + * the new link is temporarily attached + */ + mutex_lock(&configfs_symlink_mutex); spin_lock(&configfs_dirent_lock); do { struct mutex *wait_mutex; @@ -1215,6 +1220,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) if (ret) { configfs_detach_rollback(dentry); spin_unlock(&configfs_dirent_lock); + mutex_unlock(&configfs_symlink_mutex); if (ret != -EAGAIN) { config_item_put(parent_item); return ret; @@ -1224,10 +1230,12 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry) mutex_lock(wait_mutex); mutex_unlock(wait_mutex); + mutex_lock(&configfs_symlink_mutex); spin_lock(&configfs_dirent_lock); } } while (ret == -EAGAIN); spin_unlock(&configfs_dirent_lock); + mutex_unlock(&configfs_symlink_mutex); /* Get a working ref for the duration of this function */ item = configfs_get_config_item(dentry); @@ -1517,11 +1525,13 @@ 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); + mutex_lock(&configfs_symlink_mutex); spin_lock(&configfs_dirent_lock); if (configfs_detach_prep(dentry, NULL)) { printk(KERN_ERR "configfs: Tried to unregister non-empty subsystem!\n"); } spin_unlock(&configfs_dirent_lock); + mutex_unlock(&configfs_symlink_mutex); configfs_detach_group(&group->cg_item); dentry->d_inode->i_flags |= S_DEAD; mutex_unlock(&dentry->d_inode->i_mutex); diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c index c12801a12c34..61a886dbd601 100644 --- a/fs/configfs/symlink.c +++ b/fs/configfs/symlink.c @@ -31,6 +31,9 @@ #include #include "configfs_internal.h" +/* Protects attachments of new symlinks */ +DEFINE_MUTEX(configfs_symlink_mutex); + static int item_depth(struct config_item * item) { struct config_item * p = item; @@ -147,7 +150,9 @@ int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symna 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); + mutex_unlock(&configfs_symlink_mutex); if (ret && type->ct_item_ops->drop_link) type->ct_item_ops->drop_link(parent_item, target_item); -- cgit v1.2.3