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>

1 files changed, 5 insertions, 6 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 61ee85ded6ae..52444673e9a2 100644
--- 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);