Re: [PATCH v3 1/3] rust: Introduce irq module

[Boqun Feng <boqun.feng@gmail.com>]

On Thu, Aug 01, 2024 at 08:10:00PM -0400, Lyude Paul wrote:
[...]
> +/// Run the closure `cb` with interrupts disabled on the local CPU.
> +///
> +/// This creates an [`IrqDisabled`] token, which can be passed to functions that must be run
> +/// without interrupts.
> +///
> +/// # Examples
> +///
> +/// Using [`with_irqs_disabled`] to call a function that can only be called with interrupts
> +/// disabled:
> +///
> +/// ```
> +/// use kernel::irq::{IrqDisabled, with_irqs_disabled};
> +///
> +/// // Requiring interrupts be disabled to call a function
> +/// fn dont_interrupt_me(_irq: IrqDisabled<'_>) {
> +///     /* When this token is available, IRQs are known to be disabled. Actions that rely on this
> +///      * can be safely performed
> +///      */
> +/// }
> +///
> +/// // Disabling interrupts. They'll be re-enabled once this closure completes.
> +/// with_irqs_disabled(|irq| dont_interrupt_me(irq));
> +/// ```
> +#[inline]
> +pub fn with_irqs_disabled<T>(cb: impl for<'a> FnOnce(IrqDisabled<'a>) -> T) -> T {

Given the current signature, can `cb` return with interrupts enabled (if
it re-enables interrupt itself)? For example:

	with_irqs_disabled(|irq_disabled| {

	    // maybe a unsafe function.
	    reenable_irq(irq_disabled);
	})

note that `cb` is a `-> T` function, other than `-> (IrqDisabled<'a>,
T)`, so semantically, it doesn't require IRQ still disabled after
return.

Regards,
Boqun

> +    // SAFETY: FFI call with no special requirements
> +    let flags = unsafe { bindings::local_irq_save() };
> +
> +    let ret = cb(IrqDisabled(PhantomData));
> +
> +    // SAFETY: `flags` comes from our previous call to local_irq_save
> +    unsafe { bindings::local_irq_restore(flags) };
> +
> +    ret
> +}
> diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs
> index 274bdc1b0a824..ead3a7ca5ba11 100644
> --- a/rust/kernel/lib.rs
> +++ b/rust/kernel/lib.rs
> @@ -36,6 +36,7 @@
>  pub mod firmware;
>  pub mod init;
>  pub mod ioctl;
> +pub mod irq;
>  #[cfg(CONFIG_KUNIT)]
>  pub mod kunit;
>  #[cfg(CONFIG_NET)]
> -- 
> 2.45.2
> 
>