[PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Danilo Krummrich]

Given the safety requirements of as_slice_mut() and write() taking an
immutable reference is technically not incorrect.

However, let's leverage the compiler's capabilities and require a
mutable reference to ensure exclusive access.

This also fixes a clippy warning introduced with 1.88:

  warning: mutable borrow from immutable input(s)
     --> rust/kernel/dma.rs:297:78
      |
  297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
      |                                                                              ^^^^^^^^

Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
---
 rust/kernel/dma.rs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
index 25dfa0e6cc3c..2ac4c47aeed3 100644
--- a/rust/kernel/dma.rs
+++ b/rust/kernel/dma.rs
@@ -294,7 +294,7 @@ pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
     ///   slice is live.
     /// * Callers must ensure that this call does not race with a read or write to the same region
     ///   while the returned slice is live.
-    pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
+    pub unsafe fn as_slice_mut(&mut self, offset: usize, count: usize) -> Result<&mut [T]> {
         self.validate_range(offset, count)?;
         // SAFETY:
         // - The pointer is valid due to type invariant on `CoherentAllocation`,
@@ -326,7 +326,7 @@ pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T
     /// unsafe { alloc.write(buf, 0)?; }
     /// # Ok::<(), Error>(()) }
     /// ```
-    pub unsafe fn write(&self, src: &[T], offset: usize) -> Result {
+    pub unsafe fn write(&mut self, src: &[T], offset: usize) -> Result {
         self.validate_range(offset, src.len())?;
         // SAFETY:
         // - The pointer is valid due to type invariant on `CoherentAllocation`

base-commit: c7e03c5cf06a90ff234ae3c628c6b74e5cba7426
-- 
2.50.0

Re: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Alexandre Courbot]

On Sun Jun 29, 2025 at 1:49 AM JST, Danilo Krummrich wrote:
> Given the safety requirements of as_slice_mut() and write() taking an
> immutable reference is technically not incorrect.
>
> However, let's leverage the compiler's capabilities and require a
> mutable reference to ensure exclusive access.
>
> This also fixes a clippy warning introduced with 1.88:
>
>   warning: mutable borrow from immutable input(s)
>      --> rust/kernel/dma.rs:297:78
>       |
>   297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
>       |                                                                              ^^^^^^^^
>
> Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>

Re: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Abdiel Janulgue]

On 28/06/2025 19:49, Danilo Krummrich wrote:
> Given the safety requirements of as_slice_mut() and write() taking an
> immutable reference is technically not incorrect.
> 
> However, let's leverage the compiler's capabilities and require a
> mutable reference to ensure exclusive access.
> 
> This also fixes a clippy warning introduced with 1.88:
> 
>    warning: mutable borrow from immutable input(s)
>       --> rust/kernel/dma.rs:297:78
>        |
>    297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
>        |                                                                              ^^^^^^^^
> 
> Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
>   rust/kernel/dma.rs | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/rust/kernel/dma.rs b/rust/kernel/dma.rs
> index 25dfa0e6cc3c..2ac4c47aeed3 100644
> --- a/rust/kernel/dma.rs
> +++ b/rust/kernel/dma.rs
> @@ -294,7 +294,7 @@ pub unsafe fn as_slice(&self, offset: usize, count: usize) -> Result<&[T]> {
>       ///   slice is live.
>       /// * Callers must ensure that this call does not race with a read or write to the same region
>       ///   while the returned slice is live.
> -    pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
> +    pub unsafe fn as_slice_mut(&mut self, offset: usize, count: usize) -> Result<&mut [T]> {
>           self.validate_range(offset, count)?;
>           // SAFETY:
>           // - The pointer is valid due to type invariant on `CoherentAllocation`,
> @@ -326,7 +326,7 @@ pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T
>       /// unsafe { alloc.write(buf, 0)?; }
>       /// # Ok::<(), Error>(()) }
>       /// ```
> -    pub unsafe fn write(&self, src: &[T], offset: usize) -> Result {
> +    pub unsafe fn write(&mut self, src: &[T], offset: usize) -> Result {
>           self.validate_range(offset, src.len())?;
>           // SAFETY:
>           // - The pointer is valid due to type invariant on `CoherentAllocation`
> 
> base-commit: c7e03c5cf06a90ff234ae3c628c6b74e5cba7426

Reviewed-by: Abdiel Janulgue <abdiel.janulgue@gmail.com>

Re: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Andreas Hindborg]

"Danilo Krummrich" <dakr@kernel.org> writes:

> Given the safety requirements of as_slice_mut() and write() taking an
> immutable reference is technically not incorrect.
>
> However, let's leverage the compiler's capabilities and require a
> mutable reference to ensure exclusive access.
>
> This also fixes a clippy warning introduced with 1.88:
>
>   warning: mutable borrow from immutable input(s)
>      --> rust/kernel/dma.rs:297:78
>       |
>   297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
>       |                                                                              ^^^^^^^^
>
> Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>


Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>


Best regards,
Andreas Hindborg

Re: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Alice Ryhl]

On Sat, Jun 28, 2025 at 06:49:54PM +0200, Danilo Krummrich wrote:
> Given the safety requirements of as_slice_mut() and write() taking an
> immutable reference is technically not incorrect.
> 
> However, let's leverage the compiler's capabilities and require a
> mutable reference to ensure exclusive access.
> 
> This also fixes a clippy warning introduced with 1.88:
> 
>   warning: mutable borrow from immutable input(s)
>      --> rust/kernel/dma.rs:297:78
>       |
>   297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
>       |                                                                              ^^^^^^^^
> 
> Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

I'm not sure if `as_slice_mut()` is exactly the right API we want
long-term, but this is a step in the right direction.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>

Re: [PATCH] rust: dma: require mutable reference for as_slice_mut() and write()

[Danilo Krummrich]

On Sat, Jun 28, 2025 at 06:49:54PM +0200, Danilo Krummrich wrote:
> Given the safety requirements of as_slice_mut() and write() taking an
> immutable reference is technically not incorrect.
> 
> However, let's leverage the compiler's capabilities and require a
> mutable reference to ensure exclusive access.
> 
> This also fixes a clippy warning introduced with 1.88:
> 
>   warning: mutable borrow from immutable input(s)
>      --> rust/kernel/dma.rs:297:78
>       |
>   297 |     pub unsafe fn as_slice_mut(&self, offset: usize, count: usize) -> Result<&mut [T]> {
>       |                                                                              ^^^^^^^^
> 
> Fixes: d37a39f607c4 ("rust: dma: add as_slice/write functions for CoherentAllocation")
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>

Applied to alloc-next, thanks!