On Thu, Dec 22, 2011 at 01:50:46PM +0800, Li Zefan wrote:
> > @@ -2091,6 +2010,10 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
> > * rcu or tasklist locked. instead, build an array of all threads in the
> > * group - group_rwsem prevents new threads from appearing, and if
> > * threads exit, this will just be an over-estimate.
> > + *
> > + * While creating the list, also make sure css_sets exist for all
> > + * threads to be migrated. we use find_css_set, which allocates a new
> > + * one if necessary.
> > */
> > group_size = get_nr_threads(leader);
> > /* flex_array supports very large thread-groups better than kmalloc. */
> > @@ -2137,6 +2060,12 @@ int cgroup_attach_proc(struct cgroup *cgrp, struct task_struct *leader)
> > /* nothing to do if this task is already in the cgroup */
> > if (ent.cgrp == cgrp)
> > continue;
> > + ent.cg = find_css_set(tsk->cgroups, cgrp);
>
> unfortunately This won't work, because we are holding tasklist_lock.
I believe we can remove tasklist_lock now (in a seperate patch).
It was there in order to protect while_each_thread() against exec but
now we have threadgroup_lock().
I think we only need to use rcu_read_lock() to protect against concurrent
removal in exit.
> > + if (!ent.cg) {
> > + retval = -ENOMEM;
> > + group_size = i;
> > + goto out_list_teardown;
> > + }
> > retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
> > BUG_ON(retval != 0);
> > i++;
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