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

Boqun Feng
2025-03-24T18:00:46Z

On Mon, Mar 24, 2025 at 06:40:48PM +0100, Miguel Ojeda wrote:
> From: Danilo Krummrich <dakr@kernel.org>
>
> 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 <sfr@canb.auug.org.au>
> Closes: https://lore.kernel.org/linux-next/20250324215702.1515ba92@canb.auug.org.au/
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> 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 <boqun.feng@gmail.com>

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
>