1 files changed, 12 insertions, 11 deletions

diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index 750ed601ddf7..8620fd01b3d0 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -111,14 +111,11 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
 {
         if (tg != &root_task_group)
                 return false;
-
         /*
-         * We can only assume the task group can't go away on us if
-         * autogroup_move_group() can see us on ->thread_group list.
+         * If we race with autogroup_move_group() the caller can use the old
+         * value of signal->autogroup but in this case sched_move_task() will
+         * be called again before autogroup_kref_put().
          */
-        if (p->flags & PF_EXITING)
-                return false;
-
         return true;
 }
 
@@ -138,13 +135,17 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
         }
 
         p->signal->autogroup = autogroup_kref_get(ag);
-
-        if (!READ_ONCE(sysctl_sched_autogroup_enabled))
-                goto out;
-
+        /*
+         * We can't avoid sched_move_task() after we changed signal->autogroup,
+         * this process can already run with task_group() == prev->tg or we can
+         * race with cgroup code which can read autogroup = prev under rq->lock.
+         * In the latter case for_each_thread() can not miss a migrating thread,
+         * cpu_cgroup_attach() must not be possible after cgroup_exit() and it
+         * can't be removed from thread list, we hold ->siglock.
+         */
         for_each_thread(p, t)
                 sched_move_task(t);
-out:
+
         unlock_task_sighand(p, &flags);
         autogroup_kref_put(prev);
 }