config fs: avoid switching ->d_op on live dentry

Switching d_op on a live dentry is racy in general, so avoid it. In this case
it is a negative dentry, which is safer, but there are still concurrent ops
which may be called on d_op in that case (eg. d_revalidate). So in general
a filesystem may not do this. Fix configfs so as not to do this.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>

diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index 0b502f8..5787069 100644 (file)
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -232,10 +232,8 @@ int configfs_make_dirent(struct configfs_dirent * parent_sd,
 
        sd->s_mode = mode;
        sd->s_dentry = dentry;
-       if (dentry) {
+       if (dentry)
                dentry->d_fsdata = configfs_get(sd);
-               dentry->d_op = &configfs_dentry_ops;
-       }
 
        return 0;
 }
@@ -278,7 +276,6 @@ static int create_dir(struct config_item * k, struct dentry * p,
                error = configfs_create(d, mode, init_dir);
                if (!error) {
                        inc_nlink(p->d_inode);
-                       (d)->d_op = &configfs_dentry_ops;
                } else {
                        struct configfs_dirent *sd = d->d_fsdata;
                        if (sd) {
@@ -371,9 +368,7 @@ int configfs_create_link(struct configfs_symlink *sl,
                                   CONFIGFS_ITEM_LINK);
        if (!err) {
                err = configfs_create(dentry, mode, init_symlink);
-               if (!err)
-                       dentry->d_op = &configfs_dentry_ops;
-               else {
+               if (err) {
                        struct configfs_dirent *sd = dentry->d_fsdata;
                        if (sd) {
                                spin_lock(&configfs_dirent_lock);
@@ -493,7 +488,11 @@ static struct dentry * configfs_lookup(struct inode *dir,
                 * If it doesn't exist and it isn't a NOT_PINNED item,
                 * it must be negative.
                 */
-               return simple_lookup(dir, dentry, nd);
+               if (dentry->d_name.len > NAME_MAX)
+                       return ERR_PTR(-ENAMETOOLONG);
+               dentry->d_op = &configfs_dentry_ops;
+               d_add(dentry, NULL);
+               return NULL;
        }
 
 out:
@@ -685,6 +684,7 @@ static int create_default_group(struct config_group *parent_group,
        ret = -ENOMEM;
        child = d_alloc(parent, &name);
        if (child) {
+               child->d_op = &configfs_dentry_ops;
                d_add(child, NULL);
 
                ret = configfs_attach_group(&parent_group->cg_item,
@@ -1682,6 +1682,7 @@ int configfs_register_subsystem(struct configfs_subsystem *subsys)
        err = -ENOMEM;
        dentry = d_alloc(configfs_sb->s_root, &name);
        if (dentry) {
+               dentry->d_op = &configfs_dentry_ops;
                d_add(dentry, NULL);
 
                err = configfs_attach_group(sd->s_element, &group->cg_item,