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    Subject[RFC][PATCH 3/3] 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>
    ---
    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);
    --
    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


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