Re: [PATCH] rust: misc: add OWNER field to the `MiscDevice` trait

[Alice Ryhl <aliceryhl@google.com>]

On Wed, Aug 05, 2026 at 03:20:07PM +0300, Alexandru Radovici wrote:
> Add `OWNER` constant to the `MiscDevice` trait to allow modules
> to prevent unloading while the device is in use.
> 
> Set the `OWNER` field in the `rust_misc_device` example.
> 
> Signed-off-by: Alexandru Radovici <alexandru.radovici@wyliodrin.com>

This is already being solved by:
https://lore.kernel.org/all/20260723-fix-fops-owner-v9-0-c1c3af7f7bcb@linux.dev/

> This patch exposes the `owner` field of `file_operations` to the
> Rust API `MiscDevice` trait. It allows users to prevent the
> unloading of their loadable modules written in Rust
> while their `MiscDevice` is still in use.
> 
> Without this ability, writing a misc loadable module and running
> the following commands will Oops the kernel.
> 
>    # insmod misc_module.ko
>    # sleep 10 > /dev/misc_device
>    # rmmod misc_module
> 
>    ... after the sleep, the kernel Oops
> 
> I added the `OWNER` field to the `rust_misc_device` example.
> ---
>  rust/kernel/miscdevice.rs        | 13 ++++++++++++-
>  samples/rust/rust_misc_device.rs |  4 ++++
>  2 files changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/kernel/miscdevice.rs b/rust/kernel/miscdevice.rs
> index 83ce50def5ac..21c5d88c5dc4 100644
> --- a/rust/kernel/miscdevice.rs
> +++ b/rust/kernel/miscdevice.rs
> @@ -31,7 +31,7 @@
>          Opaque, //
>      },
>  };
> -use core::marker::PhantomData;
> +use core::{marker::PhantomData, ptr};
>  
>  /// Options for creating a misc device.
>  #[derive(Copy, Clone)]
> @@ -126,6 +126,12 @@ pub trait MiscDevice: Sized {
>      /// What kind of pointer should `Self` be wrapped in.
>      type Ptr: ForeignOwnable + Send + Sync;
>  
> +    /// Set the owner of this `MiscDevice` instance.
> +    ///
> +    /// In case this is compiled as a module, setting this prevents
> +    /// the module unloading while the device is still in use.
> +    const OWNER: Option<&'static ThisModule> = None;
> +
>      /// Called when the misc device is opened.
>      ///
>      /// The returned pointer will be stored as the private data for the file.
> @@ -430,6 +436,11 @@ impl<T: MiscDevice> MiscdeviceVTable<T> {
>          } else {
>              None
>          },
> +        #[cfg(CONFIG_MODULES)]
> +        owner: match T::OWNER {
> +            Some(module) => module.as_ptr(),
> +            None => ptr::null_mut(),
> +        },
>          ..pin_init::zeroed()
>      };
>  
> diff --git a/samples/rust/rust_misc_device.rs b/samples/rust/rust_misc_device.rs
> index 41e26c825060..bf8801ea3cb2 100644
> --- a/samples/rust/rust_misc_device.rs
> +++ b/samples/rust/rust_misc_device.rs
> @@ -177,6 +177,10 @@ struct RustMiscDevice {
>  impl MiscDevice for RustMiscDevice {
>      type Ptr = Pin<KBox<Self>>;
>  
> +    // Set the OWNER constant to the current module to prevent the unloading
> +    // of this module while this device is in use.
> +    const OWNER: Option<&'static ThisModule> = Some(&crate::THIS_MODULE);
> +
>      fn open(_file: &File, misc: &MiscDeviceRegistration<Self>) -> Result<Pin<KBox<Self>>> {
>          let dev = ARef::from(misc.device());
>  
> 
> ---
> base-commit: c21bb4193868a8de71fc4693fa741e195fdf5d86
> change-id: 20260805-rust_tmp-095994661956
> 
> Best regards,
> -- 
> Alexandru Radovici <alexandru.radovici@wyliodrin.com>
>