Re: [PATCH] sched/psi: fix use-after-free in ep_remove_wait_queue()

On Wed, Feb 01, 2023 at 07:00:23PM -0800, Munehisa Kamata wrote:

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c index 8ac8b81bfee6..6e66c15f6450 100644 --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -1343,10 +1343,11 @@ void psi_trigger_destroy(struct psi_trigger *t) group = t->group; /*

• * Wakeup waiters to stop polling. Can happen if cgroup is deleted
  

• * from under a polling process.
  

• * Wakeup waiters to stop polling and clear the queue to prevent it from
  

• * being accessed later. Can happen if cgroup is deleted from under a
  

• * polling process otherwise.
  

  */

• wake_up_interruptible(&t->event_wait);

• wake_up_pollfree(&t->event_wait);

mutex_lock(&group->trigger_lock);

wake_up_pollfree() should only be used in extremely rare cases. Why can't the lifetime of the waitqueue be fixed instead?

- Eric