Commit 36007727 authored by Danilo Krummrich's avatar Danilo Krummrich
Browse files

rust: drm: don't pass the address of drm::Device to drm_dev_put() 



In drm_dev_put() call in AlwaysRefCounted::dec_ref() we rely on struct
drm_device to be the first field in drm::Device, whereas everywhere
else we correctly obtain the address of the actual struct drm_device.

Analogous to the from_drm_device() helper, provide the
into_drm_device() helper in order to address this.

Fixes: 1e4b8896 ("rust: drm: add device abstraction")
Reviewed-by: default avatarAlice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20250731154919.4132-5-dakr@kernel.org


Signed-off-by: default avatarDanilo Krummrich <dakr@kernel.org>
parent 0c04a81c

rust/kernel/drm/device.rs

+18 −3
Original line number Diff line number Diff line
@@ -120,9 +120,13 @@ pub fn new(dev: &device::Device, data: impl PinInit<T::Data, Error>) -> Result<A 
        // - `raw_data` is a valid pointer to uninitialized memory.

        // - `raw_data` will not move until it is dropped.

        unsafe { data.__pinned_init(raw_data) }.inspect_err(|_| {

            // SAFETY: `__drm_dev_alloc()` was successful, hence `raw_drm` must be valid and the

            // SAFETY: `raw_drm` is a valid pointer to `Self`, given that `__drm_dev_alloc` was

            // successful.

            let drm_dev = unsafe { Self::into_drm_device(raw_drm) };



            // SAFETY: `__drm_dev_alloc()` was successful, hence `drm_dev` must be valid and the

            // refcount must be non-zero.

            unsafe { bindings::drm_dev_put(ptr::addr_of_mut!((*raw_drm.as_ptr()).dev).cast()) };

            unsafe { bindings::drm_dev_put(drm_dev) };

        })?;



        // SAFETY: The reference count is one, and now we take ownership of that reference as a
@@ -143,6 +147,14 @@ unsafe fn from_drm_device(ptr: *const bindings::drm_device) -> *mut Self { 
        unsafe { crate::container_of!(Opaque::cast_from(ptr), Self, dev) }.cast_mut()

    }



    /// # Safety

    ///

    /// `ptr` must be a valid pointer to `Self`.

    unsafe fn into_drm_device(ptr: NonNull<Self>) -> *mut bindings::drm_device {

        // SAFETY: By the safety requirements of this function, `ptr` is a valid pointer to `Self`.

        unsafe { &raw mut (*ptr.as_ptr()).dev }.cast()

    }



    /// Not intended to be called externally, except via declare_drm_ioctls!()

    ///

    /// # Safety
@@ -192,8 +204,11 @@ fn inc_ref(&self) { 
    }



    unsafe fn dec_ref(obj: NonNull<Self>) {

        // SAFETY: `obj` is a valid pointer to `Self`.

        let drm_dev = unsafe { Self::into_drm_device(obj) };



        // SAFETY: The safety requirements guarantee that the refcount is non-zero.

        unsafe { bindings::drm_dev_put(obj.cast().as_ptr()) };

        unsafe { bindings::drm_dev_put(drm_dev) };

    }

}