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

From: Miguel Ojeda
Date: Mon Mar 24 2025 - 13:52:03 EST


From: Danilo Krummrich <dakr@xxxxxxxxxx>

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@xxxxxxxxxxxxxxxx>
Closes: https://lore.kernel.org/linux-next/20250324215702.1515ba92@xxxxxxxxxxxxxxxx/
Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>
Signed-off-by: Miguel Ojeda <ojeda@xxxxxxxxxx>
---
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