db4f72c904
Checking that we are not missing any `// SAFETY` comments in our `unsafe` blocks is something we have wanted to do for a long time, as well as cleaning up the remaining cases that were not documented [1]. Back when Rust for Linux started, this was something that could have been done via a script, like Rust's `tidy`. Soon after, in Rust 1.58.0, Clippy implemented the `undocumented_unsafe_blocks` lint [2]. Even though the lint has a few false positives, e.g. in some cases where attributes appear between the comment and the `unsafe` block [3], there are workarounds and the lint seems quite usable already. Thus enable the lint now. We still have a few cases to clean up, so just allow those for the moment by writing a `TODO` comment -- some of those may be good candidates for new contributors. Link: https://github.com/Rust-for-Linux/linux/issues/351 [1] Link: https://rust-lang.github.io/rust-clippy/master/#/undocumented_unsafe_blocks [2] Link: https://github.com/rust-lang/rust-clippy/issues/13189 [3] Reviewed-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Trevor Gross <tmgross@umich.edu> Tested-by: Gary Guo <gary@garyguo.net> Reviewed-by: Gary Guo <gary@garyguo.net> Link: https://lore.kernel.org/r/20240904204347.168520-5-ojeda@kernel.org Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
76 lines
3 KiB
Rust
76 lines
3 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Allocator support.
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use super::{flags::*, Flags};
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use core::alloc::{GlobalAlloc, Layout};
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use core::ptr;
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struct KernelAllocator;
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/// Calls `krealloc` with a proper size to alloc a new object aligned to `new_layout`'s alignment.
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///
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/// # Safety
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///
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/// - `ptr` can be either null or a pointer which has been allocated by this allocator.
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/// - `new_layout` must have a non-zero size.
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pub(crate) unsafe fn krealloc_aligned(ptr: *mut u8, new_layout: Layout, flags: Flags) -> *mut u8 {
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// Customized layouts from `Layout::from_size_align()` can have size < align, so pad first.
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let layout = new_layout.pad_to_align();
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// Note that `layout.size()` (after padding) is guaranteed to be a multiple of `layout.align()`
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// which together with the slab guarantees means the `krealloc` will return a properly aligned
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// object (see comments in `kmalloc()` for more information).
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let size = layout.size();
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// SAFETY:
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// - `ptr` is either null or a pointer returned from a previous `k{re}alloc()` by the
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// function safety requirement.
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// - `size` is greater than 0 since it's from `layout.size()` (which cannot be zero according
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// to the function safety requirement)
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unsafe { bindings::krealloc(ptr as *const core::ffi::c_void, size, flags.0) as *mut u8 }
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}
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// SAFETY: TODO.
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unsafe impl GlobalAlloc for KernelAllocator {
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unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
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// SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
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// requirement.
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unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL) }
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}
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unsafe fn dealloc(&self, ptr: *mut u8, _layout: Layout) {
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// SAFETY: TODO.
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unsafe {
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bindings::kfree(ptr as *const core::ffi::c_void);
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}
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}
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unsafe fn realloc(&self, ptr: *mut u8, layout: Layout, new_size: usize) -> *mut u8 {
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// SAFETY:
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// - `new_size`, when rounded up to the nearest multiple of `layout.align()`, will not
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// overflow `isize` by the function safety requirement.
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// - `layout.align()` is a proper alignment (i.e. not zero and must be a power of two).
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let layout = unsafe { Layout::from_size_align_unchecked(new_size, layout.align()) };
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// SAFETY:
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// - `ptr` is either null or a pointer allocated by this allocator by the function safety
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// requirement.
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// - the size of `layout` is not zero because `new_size` is not zero by the function safety
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// requirement.
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unsafe { krealloc_aligned(ptr, layout, GFP_KERNEL) }
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}
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unsafe fn alloc_zeroed(&self, layout: Layout) -> *mut u8 {
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// SAFETY: `ptr::null_mut()` is null and `layout` has a non-zero size by the function safety
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// requirement.
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unsafe { krealloc_aligned(ptr::null_mut(), layout, GFP_KERNEL | __GFP_ZERO) }
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}
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}
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#[global_allocator]
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static ALLOCATOR: KernelAllocator = KernelAllocator;
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// See <https://github.com/rust-lang/rust/pull/86844>.
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#[no_mangle]
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static __rust_no_alloc_shim_is_unstable: u8 = 0;
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