On Thu, Feb 09, 2023 at 09:09:03AM -0800, Suren Baghdasaryan wrote:
On Thu, Feb 2, 2023 at 1:11 PM Suren Baghdasaryan surenb@google.com wrote:
On Wed, Feb 1, 2023 at 8:56 PM Eric Biggers ebiggers@kernel.org wrote:
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?
waitqueue lifetime in this case is linked to cgroup_file_release(), which seems appropriate to me here. Unfortunately cgroup_file_release() is not directly linked to the file's lifetime. For more details see: https://lore.kernel.org/all/CAJuCfpFZ3B4530TgsSHqp5F_gwfrDujwRYewKReJru==MdE... . So, if we want to fix the lifetime of the waitqueue, we would have to tie cgroup_file_release() to the fput() somehow. IOW, the fix would have to be done at the cgroups or higher (kernfs?) layer.
Hi Eric, Do you still object to using wake_up_pollfree() for this case? Changing higher levels to make cgroup_file_release() be tied to fput() would be ideal but I think that would be a big change for this one case. If you agree I'll Ack this patch. Thanks, Suren.
I haven't read the code closely in this case. I'm just letting you know that wake_up_pollfree() is very much a last-resort option for when the waitqueue lifetime can't be fixed. So if you want to use wake_up_pollfree(), you need to explain why no other fix is possible. For example maybe the UAPI depends on the waitqueue having a nonstandard lifetime.
- Eric