Add a Minor abstraction with RAII release and a fops_open() wrapper that holds a RegistrationGuard (drm_dev_enter / drm_dev_exit) across the entire drm_open() call.
This guarantees that drm_dev_unplug() in Registration::drop() waits for the full open sequence to complete, so all files are visible in the filelist when iterating for cleanup. Signed-off-by: Danilo Krummrich <[email protected]> --- rust/kernel/drm/device.rs | 63 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 62 insertions(+), 1 deletion(-) diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index a2940e172073..09903ed783e1 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -42,6 +42,42 @@ }, }; +/// A reference to a `struct drm_minor` with RAII release. +struct Minor(NonNull<bindings::drm_minor>); + +// Methods use `#[inline(never)]` to prevent the unexported `drm_minor_acquire()` / +// `drm_minor_release()` symbols from being inlined into driver modules. +impl Minor { + /// Acquire a minor by ID. Increments the underlying device's refcount. + #[inline(never)] + fn acquire(minor_id: u32) -> Result<Self> { + // SAFETY: `drm_minors_xa` is a valid global xarray; any `minor_id` is safe to + // look up (returns ERR_PTR on failure). + let ptr = + unsafe { bindings::drm_minor_acquire(&raw mut bindings::drm_minors_xa, minor_id) }; + Ok(Self(NonNull::new(from_err_ptr(ptr)?).ok_or(ENODEV)?)) + } + + /// Returns a reference to the DRM device for this minor. + /// + /// # Safety + /// + /// The caller must ensure that the minor belongs to a `Device<T>`. + unsafe fn device<T: drm::Driver>(&self) -> &Device<T, Userspace> { + // SAFETY: The minor is valid (from `drm_minor_acquire()`) and `minor->dev` + // is a valid `drm_device`. The caller guarantees it is a `Device<T>`. + unsafe { Device::from_raw((*self.0.as_ptr()).dev) } + } +} + +impl Drop for Minor { + #[inline(never)] + fn drop(&mut self) { + // SAFETY: `self.0` came from `drm_minor_acquire()` and has not been released yet. + unsafe { bindings::drm_minor_release(self.0.as_ptr()) } + } +} + #[cfg(CONFIG_DRM_LEGACY)] macro_rules! drm_legacy_fields { ( $($field:ident: $val:expr),* $(,)? ) => { @@ -198,11 +234,36 @@ const fn compute_features() -> u32 { fops: &Self::FOPS, }; + /// Wrapper for `fops.open` that holds a [`RegistrationGuard`] across the entire `drm_open()` + /// call. This guarantees that `drm_dev_unplug()` in `Registration::drop()` waits for the full + /// open sequence. + extern "C" fn fops_open(inode: *mut bindings::inode, filp: *mut bindings::file) -> c_int { + let f = || -> Result<c_int> { + // SAFETY: `inode` is valid. + let minor_id = unsafe { bindings::iminor(inode) }; + let minor = Minor::acquire(minor_id)?; + + // SAFETY: `fops_open` is only installed for devices of type `T` (via `FOPS`). + let _guard = (unsafe { minor.device::<T>() }) + .registration_guard() + .ok_or(ENODEV)?; + + // SAFETY: `inode` and `filp` are valid. The RegistrationGuard ensures the entire + // `drm_open()` runs within the SRCU critical section. + Ok(unsafe { bindings::drm_open(inode, filp) }) + }; + + match f() { + Ok(ret) => ret, + Err(e) => e.to_errno(), + } + } + const FOPS: bindings::file_operations = { let mut fops: bindings::file_operations = pin_init::zeroed(); fops.owner = core::ptr::null_mut(); - fops.open = Some(bindings::drm_open); + fops.open = Some(Self::fops_open); fops.release = Some(bindings::drm_release); fops.unlocked_ioctl = Some(bindings::drm_ioctl); #[cfg(CONFIG_COMPAT)] -- 2.55.0
