Re: [PATCH] cgroup: Fix potential race between cgroup_exit and migrate path

[Tejun Heo]

On Wed, Aug 30, 2017 at 05:55:45PM -0700, Tejun Heo wrote:
> Would something like the following fix the issue?  Thanks.
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index df2e0f1..cd85ca0 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -683,7 +683,7 @@ static void css_set_move_task(struct task_struct *task,
>                       if (it->task_pos == &task->cg_list)
>                               css_task_iter_advance(it);
>  
> -             list_del_init(&task->cg_list);
> +             list_del(&task->cg_list);
>               if (!css_set_populated(from_cset))
>                       css_set_update_populated(from_cset, false);
>       } else {

Oops, more like the following.

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index df2e0f1..6f34025 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -683,7 +683,7 @@ static void css_set_move_task(struct task_struct *task,
                        if (it->task_pos == &task->cg_list)
                                css_task_iter_advance(it);
 
-               list_del_init(&task->cg_list);
+               list_del(&task->cg_list);
                if (!css_set_populated(from_cset))
                        css_set_update_populated(from_cset, false);
        } else {
@@ -702,6 +702,8 @@ static void css_set_move_task(struct task_struct *task,
                rcu_assign_pointer(task->cgroups, to_cset);
                list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks 
:
                                                             &to_cset->tasks);
+       } else {
+               INIT_LIST_HEAD(&task->cg_list);
        }
 }