On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@xxxxxxxxxxxxxx> wrote:
>
> task_cs() calls cgroup_subsys_state().
You mean it calls task_subsys_state().
>
> we must use rcu_read_lock() to protect cgroup_subsys_state().
>
> it's correct that top_cpuset is never freed, but cgroup_subsys_state()
> accesses css_set, this css_set maybe freed when task_cs() called.
It would be nice to have an RCU debug mode where rcu_dereference()
does a WARN() if it's invoked not under rcu_read_lock().
>
> we use use rcu_read_lock() to protect it.
>
> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> ---
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 3e00526..e0e087e 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -363,14 +363,9 @@ void cpuset_update_task_memory_state(void)
> struct task_struct *tsk = current;
> struct cpuset *cs;
>
> - if (task_cs(tsk) == &top_cpuset) {
> - /* Don't need rcu for top_cpuset. It's never freed. */
> - my_cpusets_mem_gen = top_cpuset.mems_generation;
> - } else {
> - rcu_read_lock();
> - my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> - rcu_read_unlock();
> - }
> + rcu_read_lock();
> + my_cpusets_mem_gen = task_cs(tsk)->mems_generation;
> + rcu_read_unlock();
Yes, I guess this old cpusets assumption is no longer valid in cgroups.
Acked-by: Paul Menage <menage@xxxxxxxxxx>
Thanks
Paul
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