Subject: Re: [PATCH] rust: dma: add `Send` implementation for `CoherentAllocation`

From: Boqun Feng <[email-masked]>
Date: Mon, 24 Mar 2025 11:00:40 -0700

On Mon, Mar 24, 2025 at 06:40:48PM +0100, Miguel Ojeda wrote:
> From: Danilo Krummrich <[email-masked]>
> 
> Stephen found a future build failure in linux-next [1]:
> 
>     error[E0277]: `*mut MyStruct` cannot be sent between threads safely
>       --> samples/rust/rust_dma.rs:47:22
>        |
>     47 | impl pci::Driver for DmaSampleDriver {
>        |                      ^^^^^^^^^^^^^^^ `*mut MyStruct` cannot be sent between threads safely
> 
> It is caused by the interaction between commit 935e1d90bf6f ("rust: pci:
> require Send for Driver trait implementers") from the driver-core tree,
> which fixes a missing concurrency requirement, and commit 9901addae63b
> ("samples: rust: add Rust dma test sample driver") which adds a sample
> that does not satisfy that requirement.
> 
> Add a `Send` implementation to `CoherentAllocation`, which allows the
> sample (and other future users) to satisfy it.
> 
> Reported-by: Stephen Rothwell <[email-masked]>
> Closes: https://lore.kernel.org/linux-next/[email-masked]/
> Signed-off-by: Danilo Krummrich <[email-masked]>
> Signed-off-by: Miguel Ojeda <[email-masked]>
> ---
>  rust/kernel/dma.rs | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index 9d00f9c49f47..18de693c4924 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -301,6 +301,10 @@ fn drop(&mut self) {
>      }
>  }
>  
> +// SAFETY: It is safe to send a `CoherentAllocation` to another thread if `T`
> +// can be send to another thread.

s/can be send/can be sent

Reviewed-by: Boqun Feng <[email-masked]>

Regards,
Boqun

> +unsafe impl<T: AsBytes + FromBytes + Send> Send for CoherentAllocation<T> {}
> +
>  /// Reads a field of an item from an allocated region of structs.
>  ///
>  /// # Examples
> -- 
> 2.49.0
>