Re: [PATCH v4 02/28] rust: alloc: separate `aligned_size` from `krealloc_aligned`

Benno Lossin
2024-08-06T16:06:22Z

On 05.08.24 17:19, Danilo Krummrich wrote:
> Separate `aligned_size` from `krealloc_aligned`.
>
> Subsequent patches implement `Allocator` derivates, such as `Kmalloc`,
> that require `aligned_size` and replace the original `krealloc_aligned`.
>
> Reviewed-by: Alice Ryhl <aliceryhl@google.com>
> Signed-off-by: Danilo Krummrich <dakr@kernel.org>
> ---
> rust/kernel/alloc/allocator.rs | 27 ++++++++++++++++++---------
> 1 file changed, 18 insertions(+), 9 deletions(-)
>
> diff --git a/rust/kernel/alloc/allocator.rs b/rust/kernel/alloc/allocator.rs
> index e6ea601f38c6..e7b7eba84acb 100644
> --- a/rust/kernel/alloc/allocator.rs
> +++ b/rust/kernel/alloc/allocator.rs
> @@ -8,27 +8,36 @@
>
> struct KernelAllocator;
>
> -/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
> -///
> -/// # Safety
> -///
> -/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
> -/// - `new_layout` must have a non-zero size.
> -pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
> +/// Returns a proper size to alloc a new object aligned to `new_layout`'s alignment.
> +fn aligned_size(new_layout: Layout) -> usize {
> // Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
> let layout = new_layout.pad_to_align();
>
> // Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
> // which together with the slab guarantees means the `krealloc` will return a properly aligned
> // object (see comments in `kmalloc()` for more information).
> - let size = layout.size();
> + layout.size()
> +}
>
> +/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
> +///
> +/// # Safety
> +///
> +/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
> +/// - `new_layout` must have a non-zero size.
> +pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
> // SAFETY:
> // - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
> // function safety requirement.
> // - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
> // to the function safety requirement)
> - unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
> + unsafe {
> + bindings::krealloc(
> + ptr as *const core::ffi::c_void,
> + aligned_size(new_layout),

Can you move the safe operation outside of the `unsafe` block?

With that changed,

Reviewed-by: Benno Lossin <benno.lossin@proton.me>

---
Cheers,
Benno

> + flags.0,
> + ) as *mut u8
> + }
> }
>
> unsafe impl GlobalAlloc for KernelAllocator {
> --
> 2.45.2
>