On Wed, 21 Oct 2026 09:38:07 +0000
Alice Ryhl <[email protected]> wrote:
> On Sun, Aug 23, 2026 at 01:50:08PM +0300, Onur Özkan wrote:
> > @@ -56,7 +57,7 @@ pub(crate) struct TyrPlatformDriverData<'bound> {
> > // ensure the correct drop order.
> > #[pin]
> > _reset: reset::ResetHandle<'bound>,
> > - _reg: drm::Registration<'bound, TyrDrmDriver>,
> > + _reg: Arc<Revocable<drm::Registration<'bound, TyrDrmDriver>>>,
> > _device: ARef<TyrDrmDevice>,
> > }
> >
> > @@ -161,17 +162,18 @@ fn probe<'bound>(
> > gpu_info,
> > });
> >
> > - // SAFETY: `reg` is stored in the platform driver data and is
> > not leaked or
> > - // forgotten, so it is dropped before the `'bound`
> > registration data can become
> > - // invalid.
> > + // SAFETY: `reg` is wrapped in a `Revocable` owned by the
> > platform driver
> > + // data and its reset handle. Neither is leaked or forgotten,
> > so `reg` is
> > + // dropped before the `'bound` registration data can become
> > invalid.
> > let reg =
> > unsafe { drm::Registration::new_with_lt(pdev.as_ref(),
> > unreg_dev, reg_data, 0)? };
> > let device = reg.device().into();
> > + let reg = Arc::pin_init(Revocable::new(reg), GFP_KERNEL)?;
>
> `drm::Registration::new` requires that the `Registration` is dropped
> before `'bound` expires so that `drm_dev_unplug()` runs and
> `TyrDrmRegistrationData<'bound>` is dropped while `'bound` is still
> valid. Wrapping it in an `Arc` makes this invariant fragile: if any
> `Arc` clone outlives `TyrPlatformDriverData` or is leaked,
> `drm::Registration` will not be dropped on platform unbind and
> `TyrDrmRegistrationData<'bound>` will outlive `'bound`.
>
> With `pin-init`'s new safe self-referential struct support in `rust-next`
> (see e.g. [1]), you can avoid both `Arc` and raw pointers altogether by
> storing `_reg: Revocable<drm::Registration<'bound, TyrDrmDriver>>`
> directly as a `#[pin]` field of `TyrPlatformDriverData<'bound>` and
> having `_reset` borrow it via field + existential lifetimes:
>
> #[pin_data]
> pub(crate) struct TyrPlatformDriverData<'bound> {
> #[pin]
> #[uses('_reg: invariant)]
> _reset: reset::ResetHandle<'_reg>,
> #[pin]
> _reg: Revocable<drm::Registration<'bound, TyrDrmDriver>>,
> }
>
> and in `reset.rs`:
>
> #[pin_data]
> struct Controller<'ctrl>
> where
> exists<'bound>: 'ctrl,
> {
> pdev: &'ctrl platform::Device<Bound>,
> state: Atomic<ResetState>,
> hw: Arc<HwGate<'ctrl>>,
> #[uses('bound: invariant)]
> registration:
> Pin<&'ctrl Revocable<drm::Registration<'bound, TyrDrmDriver>>>,
> }
>
> Then `probe()` simply initializes `_reg` first and passes `_reg` to
> `ResetHandle::new(pdev, hw, _reg)?`, `reset_work()` calls
> `self.with_registration(|reg| reg.revoke())`, and `#[pin_data]`
> statically checks that `_reset` drops before `_reg`.
>
> Also, as a heads-up for rebasing onto `drm-rust-next`:
> `_device: ARef<TyrDrmDevice>` has been removed from
> `TyrPlatformDriverData` (along with the empty `PinnedDrop` impl), and
> `drm::Registration::new()` now returns `impl PinInit<Self, Error>`
> directly without the `flags` argument, so `_reg` can be initialized in
> place via `Revocable::new(unsafe { drm::Registration::new(...) })`.
>
> [1] https://lore.kernel.org/r/[email protected]
>
> Alice
Any idea when will we push drm-rust-next changes into rust-next?
- Onur
