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configfs: Protect configfs_dirent s_links list mutations 

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>
Signed-off-by: Joel Becker <joel.becker@oracle.com>
This commit is contained in:
Louis Rilling 2008-06-16 19:00:59 +02:00 committed by Mark Fasheh
parent 6f61076406
commit 5301a77da2
2 changed files with 9 additions and 4 deletions
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5
fs/configfs/dir.c
View File

@ -37,10 +37,11 @@
DECLARE_RWSEM(configfs_rename_sem);
/*
* Protects mutations of configfs_dirent linkage together with proper i_mutex
* Also protects mutations of symlinks linkage to target configfs_dirent
* Mutators of configfs_dirent linkage must *both* have the proper inode locked
* and configfs_dirent_lock locked, in that order.
* This allows one to safely traverse configfs_dirent trees without having to
* lock inodes.
* This allows one to safely traverse configfs_dirent trees and symlinks without
* having to lock inodes.
*/
DEFINE_SPINLOCK(configfs_dirent_lock);

8
fs/configfs/symlink.c
View File

@ -77,12 +77,15 @@ static int create_link(struct config_item *parent_item,
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);
}
@ -186,8 +189,9 @@ int configfs_unlink(struct inode *dir, struct dentry *dentry)
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);