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

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

[Miguel Ojeda]

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.
+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

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

[Miguel Ojeda]

On Mon, Mar 24, 2025 at 6:41 PM Miguel Ojeda <ojeda@kernel.org> 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>

If nobody shouts in the next few hours, I will apply it to `rust-next`
to clean the build failure for tomorrow's linux-next.

Abdiel: if you can give an Acked-by, that would be great.

Thanks!

Cheers,
Miguel

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

[Boqun Feng]

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
> 

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

[Miguel Ojeda]

On Mon, Mar 24, 2025 at 6:41 PM Miguel Ojeda <ojeda@kernel.org> 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>

Applied to `rust-next` -- thanks everyone!

    [ Added number to Closes. Fix typo spotted by Boqun. - Miguel ]

Cheers,
Miguel