Re: [PATCH] cgroups: fix lock inconsistency in cgroup_clone()

[Paul Menage <menage@google.com>]

On Mon, Jan 19, 2009 at 10:43 PM, Li Zefan <lizf@cn.fujitsu.com> wrote:
> I fixed a bug in cgroup_clone() in Linus' tree (commit 7b574b7), without
> noticing there was a cleanup patch in -mm tree that should be rebased
> (now commit 104cbd5), thus resulted in lock inconsistency.
>
> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>

Acked-by: Paul Menage <menage@google.com>

Thanks.

> ---
>
> for 2.6.29
>
> ---
>  kernel/cgroup.c |   13 +++++++------
>  1 files changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index c298310..a5826f3 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2991,20 +2991,21 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
>                mutex_unlock(&cgroup_mutex);
>                return 0;
>        }
> -       task_lock(tsk);
> -       cg = tsk->cgroups;
> -       parent = task_cgroup(tsk, subsys->subsys_id);
>
>        /* Pin the hierarchy */
> -       if (!atomic_inc_not_zero(&parent->root->sb->s_active)) {
> +       if (!atomic_inc_not_zero(&root->sb->s_active)) {
>                /* We race with the final deactivate_super() */
>                mutex_unlock(&cgroup_mutex);
>                return 0;
>        }
>
>        /* Keep the cgroup alive */
> +       task_lock(tsk);
> +       parent = task_cgroup(tsk, subsys->subsys_id);
> +       cg = tsk->cgroups;
>        get_css_set(cg);
>        task_unlock(tsk);
> +
>        mutex_unlock(&cgroup_mutex);
>
>        /* Now do the VFS work to create a cgroup */
> @@ -3043,7 +3044,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
>                mutex_unlock(&inode->i_mutex);
>                put_css_set(cg);
>
> -               deactivate_super(parent->root->sb);
> +               deactivate_super(root->sb);
>                /* The cgroup is still accessible in the VFS, but
>                 * we're not going to try to rmdir() it at this
>                 * point. */
> @@ -3069,7 +3070,7 @@ int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys,
>        mutex_lock(&cgroup_mutex);
>        put_css_set(cg);
>        mutex_unlock(&cgroup_mutex);
> -       deactivate_super(parent->root->sb);
> +       deactivate_super(root->sb);
>        return ret;
>  }
>
> --
> 1.5.4.rc3
>
>
>