[RFC][PATCH 3/3] configfs: Protect configfs_dirent s_links list mutations

Louis Rilling
2008-06-12T15:31:45Z

[-- Attachment #1: configfs-fix-symlink-dirent-linkage-locking.patch --]
[-- Type: text/plain, Size: 2020 bytes --]

Symlinks to a config_item are listed under its configfs_dirent s_links, but the
list mutations are not protected by any common lock.

This patch uses the configfs_dirent_lock spinlock to add the necessary
protection.

Note: we should also protect the list_empty() test in configfs_detach_prep() but
1/ the lock should not be released immediately because nothing would prevent the
list from being filled after a successful list_empty() test, making the problem
tricky,
2/ this will be solved by the rmdir() vs rename() deadlock bugfix.

Signed-off-by: Louis Rilling <Louis.Rilling@kerlabs.com>
---
fs/configfs/symlink.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

Index: b/fs/configfs/symlink.c
===================================================================
--- a/fs/configfs/symlink.c 2008-06-12 16:50:40.000000000 +0200
+++ b/fs/configfs/symlink.c 2008-06-12 16:52:43.000000000 +0200
@@ -77,12 +77,15 @@ static int create_link(struct config_ite
sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
if (sl) {
sl->sl_target = config_item_get(item);
- /* FIXME: needs a lock, I'd bet */
+ spin_lock(&configfs_dirent_lock);
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);
}
@@ -190,8 +193,9 @@ int configfs_unlink(struct inode *dir, s
type->ct_item_ops->drop_link(parent_item,
sl->sl_target);

- /* FIXME: Needs lock */
+ spin_lock(&configfs_dirent_lock);
list_del_init(&sl->sl_list);
+ spin_unlock(&configfs_dirent_lock);

/* Put reference from create_link() */
config_item_put(sl->sl_target);