cgroup: keep css_set and task lists in chronological order

css task iteration will be updated to not leak cgroup internal locking
to iterator users.  In preparation, update css_set and task lists to
be in chronological order.

For tasks, as migration path is already using list_splice_tail_init(),
only cgroup_enable_task_cg_lists() and cgroup_post_fork() need
updating.  For css_sets, link_css_set() is the only place which needs
to be updated.

Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 61ee85d..5244467 100644 (file)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -914,12 +914,11 @@ static void link_css_set(struct list_head *tmp_links, struct css_set *cset,
        link->cset = cset;
        link->cgrp = cgrp;
 
-       list_move(&link->cset_link, &cgrp->cset_links);
-
        /*
-        * Always add links to the tail of the list so that the list
-        * is sorted by order of hierarchy creation
+        * Always add links to the tail of the lists so that the lists are
+        * in choronological order.
         */
+       list_move_tail(&link->cset_link, &cgrp->cset_links);
        list_add_tail(&link->cgrp_link, &cset->cgrp_links);
 
        if (cgroup_parent(cgrp))
@@ -1780,7 +1779,7 @@ static void cgroup_enable_task_cg_lists(void)
 
                        if (!css_set_populated(cset))
                                css_set_update_populated(cset, true);
-                       list_add(&p->cg_list, &cset->tasks);
+                       list_add_tail(&p->cg_list, &cset->tasks);
                        get_css_set(cset);
                }
                spin_unlock_irq(&p->sighand->siglock);
@@ -5480,7 +5479,7 @@ void cgroup_post_fork(struct task_struct *child,
                cset = task_css_set(current);
                if (list_empty(&child->cg_list)) {
                        rcu_assign_pointer(child->cgroups, cset);
-                       list_add(&child->cg_list, &cset->tasks);
+                       list_add_tail(&child->cg_list, &cset->tasks);
                        get_css_set(cset);
                }
                up_write(&css_set_rwsem);