linux-kernel - Re: [PATCH v4 1/2] rust: allocator: add unit tests of kmalloc, vmalloc and kvmalloc

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Message-Id: <DBKERZ03P2WS.3HQ0NZC9OO5AZ@kernel.org>
Date: Thu, 24 Jul 2025 17:59:39 +0200
From: "Danilo Krummrich" <dakr@...nel.org>
To: "Hui Zhu" <hui.zhu@...ux.dev>
Cc: "Lorenzo Stoakes" <lorenzo.stoakes@...cle.com>, "Vlastimil Babka"
 <vbabka@...e.cz>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, "Uladzislau
 Rezki" <urezki@...il.com>, "Miguel Ojeda" <ojeda@...nel.org>, "Alex Gaynor"
 <alex.gaynor@...il.com>, "Boqun Feng" <boqun.feng@...il.com>, "Gary Guo"
 <gary@...yguo.net>, <bjorn3_gh@...tonmail.com>, "Benno Lossin"
 <lossin@...nel.org>, "Andreas Hindborg" <a.hindborg@...nel.org>, "Alice
 Ryhl" <aliceryhl@...gle.com>, "Trevor Gross" <tmgross@...ch.edu>,
 <rust-for-linux@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Hui Zhu"
 <zhuhui@...inos.cn>, "Geliang Tang" <geliang@...nel.org>
Subject: Re: [PATCH v4 1/2] rust: allocator: add unit tests of kmalloc,
 vmalloc and kvmalloc

On Thu Jul 24, 2025 at 11:25 AM CEST, Hui Zhu wrote:
> From: Hui Zhu <zhuhui@...inos.cn>
>
> Add KUnit test cases to validate the functionality of Rust allocation
> wrappers (kmalloc, vmalloc, kvmalloc).
>
> The tests include:
> Basic allocation tests for each allocator using a 1024-byte Blob
> structure initialized with a 0xfe pattern.
> Large alignment (> PAGE_SIZE) allocation testing using an 8192-byte
> aligned LargeAlignBlob structure.
> Verification of allocation constraints:
> - kmalloc successfully handles large alignments.
> - vmalloc and kvmalloc correctly fail for unsupported large alignments.
> Content verification through byte-by-byte pattern checking.
>
> Co-developed-by: Geliang Tang <geliang@...nel.org>
> Signed-off-by: Geliang Tang <geliang@...nel.org>
> Signed-off-by: Hui Zhu <zhuhui@...inos.cn>

Thanks for the patch, additional test are always welcome! :)

> ---
>  rust/kernel/alloc/allocator.rs | 57 ++++++++++++++++++++++++++++++++++
>  1 file changed, 57 insertions(+)
>
> diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
> index aa2dfa9dca4c..430d1f664fdf 100644
> --- a/rust/kernel/alloc/allocator.rs
> +++ b/rust/kernel/alloc/allocator.rs
> @@ -187,3 +187,60 @@ unsafe fn realloc(
>          unsafe { ReallocFunc::KVREALLOC.call(ptr, layout, old_layout, flags) }
>      }
>  }
> +
> +#[macros::kunit_tests(rust_allocator_kunit)]
> +mod tests {
> +    use super::*;
> +    use kernel::prelude::*;
> +
> +    const TEST_SIZE: usize = 1024;
> +    const LARGE_ALIGN_TEST_SIZE: usize = kernel::page::PAGE_SIZE * 4;
> +    #[repr(align(128))]
> +    struct Blob([u8; TEST_SIZE]);
> +    // This structure is used to test the allocation of alignments larger
> +    // than PAGE_SIZE.
> +    // Since this is not yet supported, avoid accessing the contents of
> +    // the structure for now.
> +    #[allow(dead_code)]
> +    #[repr(align(8192))]
> +    struct LargeAlignBlob([u8; LARGE_ALIGN_TEST_SIZE]);
> +
> +    #[test]
> +    fn test_kmalloc() -> Result<(), AllocError> {
> +        let blob = KBox::new(Blob([0xfeu8; TEST_SIZE]), GFP_KERNEL)?;

Since those are now actual unit tests on the Allocator implementations, it would
be fine to use them directly. However, for the case you are testing here, i.e.
alignment using Box is perfectly fine.

Having that said, I wouldn't call those tests test_*malloc(), since they're not
really testing all aspects of a certain allocator, but only the success to
allocate with certain alignment arguments.

Instead, I propose to write just a single test, test_alignment(), with a few
helper functions.

For instance, your Blob test structure could have a constructor that is generic
over A: Allocator.

However, given that you really only want to check alignment, you probably want a
structure like this instead.

	struct TestAlign<A: Allocator>(Box<MaybeUninit<[u8; TEST_SIZE]>, A>);

	impl<A: Allocator> TestAlign<A> {
	   fn new() -> Result<Self> {
	      Box::<_, A>::new_uninit(GFP_KERNEL)
	   }

	   fn alignment_valid(&self) -> bool {
	      ...
	   }
	}

and then test_alignment() can just do

	let test = TestAlign::<Kmalloc>::new()?;
	assert!(test.alignment_valid());

	...

Given that this is now a unit test I also think that actually validating the
alignment of the pointer Box wraps makes sense, similar to what you had in v2.

> +        for b in blob.0.as_slice().iter() {
> +            assert_eq!(*b, 0xfeu8);
> +        }

I don't think that this has any valid in the context of testing alignment.

> +        let blob = KBox::new(LargeAlignBlob([0xfdu8; LARGE_ALIGN_TEST_SIZE]), GFP_KERNEL)?;

For the large alignment case, you can consider to let TestAlign take a const
generic, additional to A: Allocator, e.g.

	struct TestAlign<A: Allocator, const SIZE: usize>(Box<MaybeUninit<[u8; SIZE]>, A>);

This way you can keep test_alignment() function very compact.

- Danilo