Re: [RFC][-mm] Add an owner to the mm_struct (v4)

["Paul Menage" <menage@google.com>]

On Tue, Apr 1, 2008 at 8:25 PM, Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
>
>  > +assign_new_owner:
>  > +     rcu_read_unlock();
>  > +     BUG_ON(c == p);
>  > +     task_lock(c);
>  > +     if (c->mm != mm) {
>  > +             task_unlock(c);
>  > +             goto retry;
>  > +     }
>  > +     cgroup_mm_owner_callbacks(mm->owner, c);
>  > +     mm->owner = c;
>  > +     task_unlock(c);
>  > +}
>  > Why rcu_read_unlock() before changing owner ? Is it safe ?
>  >
>
>  It should be safe, since we take task_lock(), but to be doubly sure, we can drop
>  rcu read lock after taking the task_lock().
>

I agree with Kamezawa - the task can technically disappear as soon as
we leave the RCU critical section. (In practice, it'll only happen
with CONFIG_PREEMPT).

Paul