Re: [PATCH v2 3/7] rust: always inline some init methods

[Gary Guo]

On Wed May 27, 2026 at 12:52 PM BST, Alexandre Courbot wrote:
> These methods should always be inlined for optimization reasons. Failure
> to do so can also produce symbol names larger than what `modpost`
> supports.
>
> Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx>
> ---
>  rust/kernel/alloc/kbox.rs | 2 ++
>  rust/kernel/init.rs       | 1 +
>  rust/kernel/sync/arc.rs   | 2 ++
>  rust/kernel/types.rs      | 3 +++
>  4 files changed, 8 insertions(+)
>
> diff --git a/rust/kernel/alloc/kbox.rs b/rust/kernel/alloc/kbox.rs
> index 2f8c16473c2c..592fffc72e52 100644
> --- a/rust/kernel/alloc/kbox.rs
> +++ b/rust/kernel/alloc/kbox.rs
> @@ -433,6 +433,7 @@ impl<T, A> InPlaceWrite<T> for Box<MaybeUninit<T>, A>
>  {
>      type Initialized = Box<T, A>;
>  
> +    #[inline(always)]
>      fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> {
>          let slot = self.as_mut_ptr();
>          // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
> @@ -442,6 +443,7 @@ fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E
>          Ok(unsafe { Box::assume_init(self) })
>      }
>  
> +    #[inline(always)]
>      fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> {
>          let slot = self.as_mut_ptr();
>          // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
> diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
> index 7a0d4559d7b5..36d4bf1959fb 100644
> --- a/rust/kernel/init.rs
> +++ b/rust/kernel/init.rs
> @@ -151,6 +151,7 @@ fn try_pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> Result<Self::Pinne
>      /// type.
>      ///
>      /// If `T: !Unpin` it will not be able to move afterwards.
> +    #[inline(always)]
>      fn pin_init<E>(init: impl PinInit<T, E>, flags: Flags) -> error::Result<Self::PinnedSelf>
>      where
>          Error: From<E>,
> diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
> index 18d6c0d62ce0..973f15165606 100644
> --- a/rust/kernel/sync/arc.rs
> +++ b/rust/kernel/sync/arc.rs
> @@ -712,6 +712,7 @@ fn try_init<E>(init: impl Init<T, E>, flags: Flags) -> Result<Self, E>
>  impl<T> InPlaceWrite<T> for UniqueArc<MaybeUninit<T>> {
>      type Initialized = UniqueArc<T>;
>  
> +    #[inline(always)]
>      fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E> {
>          let slot = self.as_mut_ptr();
>          // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
> @@ -721,6 +722,7 @@ fn write_init<E>(mut self, init: impl Init<T, E>) -> Result<Self::Initialized, E
>          Ok(unsafe { self.assume_init() })
>      }
>  
> +    #[inline(always)]
>      fn write_pin_init<E>(mut self, init: impl PinInit<T, E>) -> Result<Pin<Self::Initialized>, E> {
>          let slot = self.as_mut_ptr();
>          // SAFETY: When init errors/panics, slot will get deallocated but not dropped,
> diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs
> index ac316fd7b538..381a06ee0d59 100644
> --- a/rust/kernel/types.rs
> +++ b/rust/kernel/types.rs
> @@ -367,6 +367,7 @@ pub const fn zeroed() -> Self {
>      /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
>      /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
>      /// to verify at that point that the inner value is valid.
> +    #[inline(always)]
>      pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
>          // SAFETY: We contain a `MaybeUninit`, so it is OK for the `init_func` to not fully
>          // initialize the `T`.

Are you sure this (and other `impl PinInit`-returning functions) are actually
causing issue? They just return an initializer and the actual init code is not
marked as `#[inline]`.

Best,
Gary

> @@ -386,6 +387,7 @@ pub fn ffi_init(init_func: impl FnOnce(*mut T)) -> impl PinInit<Self> {
>      /// This function is safe, because the `T` inside of an `Opaque` is allowed to be
>      /// uninitialized. Additionally, access to the inner `T` requires `unsafe`, so the caller needs
>      /// to verify at that point that the inner value is valid.
> +    #[inline(always)]
>      pub fn try_ffi_init<E>(
>          init_func: impl FnOnce(*mut T) -> Result<(), E>,
>      ) -> impl PinInit<Self, E> {
> @@ -417,6 +419,7 @@ pub const fn cast_from(this: *const T) -> *const Self {
>  
>  impl<T> Wrapper<T> for Opaque<T> {
>      /// Create an opaque pin-initializer from the given pin-initializer.
> +    #[inline(always)]
>      fn pin_init<E>(slot: impl PinInit<T, E>) -> impl PinInit<Self, E> {
>          Self::try_ffi_init(|ptr: *mut T| {
>              // SAFETY: