diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 37b6d534b0ca..98a8045e2149 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -1761,7 +1761,14 @@ static void cgroup_task_migrate(struct cgroup *old_cgrp, get_css_set(new_cset); rcu_assign_pointer(tsk->cgroups, new_cset); - list_move(&tsk->cg_list, &new_cset->mg_tasks); + + /* + * Use move_tail so that cgroup_taskset_first() still returns the + * leader after migration. This works because cgroup_migrate() + * ensures that the dst_cset of the leader is the first on the + * tset's dst_csets list. + */ + list_move_tail(&tsk->cg_list, &new_cset->mg_tasks); /* * We just gained a reference on old_cset by taking it from the @@ -1936,9 +1943,16 @@ static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader, if (!cset->mg_src_cgrp) goto next; - list_move(&task->cg_list, &cset->mg_tasks); - list_move(&cset->mg_node, &tset.src_csets); - list_move(&cset->mg_dst_cset->mg_node, &tset.dst_csets); + /* + * cgroup_taskset_first() must always return the leader. + * Take care to avoid disturbing the ordering. + */ + list_move_tail(&task->cg_list, &cset->mg_tasks); + if (list_empty(&cset->mg_node)) + list_add_tail(&cset->mg_node, &tset.src_csets); + if (list_empty(&cset->mg_dst_cset->mg_node)) + list_move_tail(&cset->mg_dst_cset->mg_node, + &tset.dst_csets); next: if (!threadgroup) break; @@ -1999,7 +2013,7 @@ static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader, down_write(&css_set_rwsem); list_splice_init(&tset.dst_csets, &tset.src_csets); list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) { - list_splice_init(&cset->mg_tasks, &cset->tasks); + list_splice_tail_init(&cset->mg_tasks, &cset->tasks); list_del_init(&cset->mg_node); } up_write(&css_set_rwsem);