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Date: Fri, 23 Jun 2023 10:35:00 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: bjorn3_gh@...tonmail.com
Cc: Miguel Ojeda <ojeda@...nel.org>,
Alex Gaynor <alex.gaynor@...il.com>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Gary Guo <gary@...yguo.net>,
Benno Lossin <benno.lossin@...ton.me>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rust: alloc: Add realloc and alloc_zeroed to the
GlobalAlloc impl
On Thu, Jun 22, 2023 at 09:24:40PM +0200, Björn Roy Baron via B4 Relay wrote:
> From: Björn Roy Baron <bjorn3_gh@...tonmail.com>
>
> While there are default impls for these methods, using the respective C
> api's is faster. Currently neither the existing nor these new
> GlobalAlloc method implementations are actually called. Instead the
> __rust_* function defined below the GlobalAlloc impl are used. With
> rustc 1.71 these functions will be gone and all allocation calls will go
> through the GlobalAlloc implementation.
>
> Link: https://github.com/Rust-for-Linux/linux/issues/68
Nice! Although I think we need to do the simialr size adjustment as:
https://lore.kernel.org/rust-for-linux/20230613164258.3831917-1-boqun.feng@gmail.com/
so I applied your patch onto my patch and came up with the following:
--------------------------------->8
diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
index ce7a06bf7589..af723c2924dc 100644
--- a/rust/kernel/allocator.rs
+++ b/rust/kernel/allocator.rs
@@ -9,8 +9,17 @@
struct KernelAllocator;
-unsafe impl GlobalAlloc for KernelAllocator {
- unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+impl KernelAllocator {
+ /// # Safety
+ ///
+ /// * `ptr` can be either null or a pointer which has been allocated by this allocator.
+ /// * `layout` must have a non-zero size.
+ unsafe fn krealloc_with_flags(
+ &self,
+ ptr: *mut u8,
+ layout: Layout,
+ flags: bindings::gfp_t,
+ ) -> *mut u8 {
// Customized layouts from `Layout::from_size_align()` can have size < align, so pads first.
let layout = layout.pad_to_align();
@@ -26,9 +35,22 @@ unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
size = size.next_power_of_two();
}
- // `krealloc()` is used instead of `kmalloc()` because the latter is
- // an inline function and cannot be bound to as a result.
- unsafe { bindings::krealloc(ptr::null(), size, bindings::GFP_KERNEL) as *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 either a `layout.size()` (which cannot be zero
+ // according to the function safety requirement) or a result from `next_power_of_two()`.
+ unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags) as *mut u8 }
+ }
+}
+
+unsafe impl GlobalAlloc for KernelAllocator {
+ unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
+ // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+ // requirement.
+ unsafe { self.krealloc_with_flags(ptr::null_mut(), layout, bindings::GFP_KERNEL) }
}
unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
@@ -37,23 +59,30 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
}
}
- unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: usize) -> *mut u8 {
- unsafe {
- bindings::krealloc(
- ptr as *const core::ffi::c_void,
- new_size,
- bindings::GFP_KERNEL,
- ) as *mut u8
- }
+ unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
+ // SAFETY:
+ // * `new_size` when rounded up to the nearest multiple of `layout.align()`, will not
+ // overflow `isize` by the function safety requirement.
+ // * `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
+ let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
+
+ // SAFETY:
+ // * `ptr` is either null or a pointer allocated by this allocator by function safety
+ // requirement.
+ // * the size of `layout` is not zero because `new_size` is not zero by function safety
+ // requirement.
+ unsafe { self.krealloc_with_flags(ptr, layout, bindings::GFP_KERNEL) }
}
unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
+ // SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
+ // requirement.
unsafe {
- bindings::krealloc(
- core::ptr::null(),
- layout.size(),
+ self.krealloc_with_flags(
+ ptr::null_mut(),
+ layout,
bindings::GFP_KERNEL | bindings::__GFP_ZERO,
- ) as *mut u8
+ )
}
}
}
Regards,
Boqun
> Signed-off-by: Björn Roy Baron <bjorn3_gh@...tonmail.com>
> ---
> rust/kernel/allocator.rs | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/rust/kernel/allocator.rs b/rust/kernel/allocator.rs
> index 397a3dd57a9b..e0a27b1326b5 100644
> --- a/rust/kernel/allocator.rs
> +++ b/rust/kernel/allocator.rs
> @@ -21,6 +21,26 @@ unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
> bindings::kfree(ptr as *const core::ffi::c_void);
> }
> }
> +
> + unsafe fn realloc(&self, ptr: *mut u8, _layout: Layout, new_size: usize) -> *mut u8 {
> + unsafe {
> + bindings::krealloc(
> + ptr as *const core::ffi::c_void,
> + new_size,
> + bindings::GFP_KERNEL,
> + ) as *mut u8
> + }
> + }
> +
> + unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
> + unsafe {
> + bindings::krealloc(
> + core::ptr::null(),
> + layout.size(),
> + bindings::GFP_KERNEL | bindings::__GFP_ZERO,
> + ) as *mut u8
> + }
> + }
> }
>
> #[global_allocator]
>
> ---
> base-commit: d2e3115d717197cb2bc020dd1f06b06538474ac3
> change-id: 20230622-global_alloc_methods-abf5b5e38dba
>
> Best regards,
> --
> Björn Roy Baron <bjorn3_gh@...tonmail.com>
>
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