diff options
Diffstat (limited to 'rust/kernel/sync/arc.rs')
| -rw-r--r-- | rust/kernel/sync/arc.rs | 63 |
1 files changed, 23 insertions, 40 deletions
diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 63a66761d0c7..289f77abf415 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -8,7 +8,7 @@ //! threads. //! //! It is different from the standard library's [`Arc`] in a few ways: -//! 1. It is backed by the kernel's `refcount_t` type. +//! 1. It is backed by the kernel's [`Refcount`] type. //! 2. It does not support weak references, which allows it to be half the size. //! 3. It saturates the reference count instead of aborting when it goes over a threshold. //! 4. It does not provide a `get_mut` method, so the ref counted object is pinned. @@ -18,16 +18,16 @@ use crate::{ alloc::{AllocError, Flags, KBox}, - bindings, ffi::c_void, + fmt, init::InPlaceInit, + sync::Refcount, try_init, - types::{ForeignOwnable, Opaque}, + types::ForeignOwnable, }; use core::{ alloc::Layout, borrow::{Borrow, BorrowMut}, - fmt, marker::PhantomData, mem::{ManuallyDrop, MaybeUninit}, ops::{Deref, DerefMut}, @@ -145,7 +145,7 @@ pub struct Arc<T: ?Sized> { #[pin_data] #[repr(C)] struct ArcInner<T: ?Sized> { - refcount: Opaque<bindings::refcount_t>, + refcount: Refcount, data: T, } @@ -157,7 +157,7 @@ impl<T: ?Sized> ArcInner<T> { /// `ptr` must have been returned by a previous call to [`Arc::into_raw`], and the `Arc` must /// not yet have been destroyed. unsafe fn container_of(ptr: *const T) -> NonNull<ArcInner<T>> { - let refcount_layout = Layout::new::<bindings::refcount_t>(); + let refcount_layout = Layout::new::<Refcount>(); // SAFETY: The caller guarantees that the pointer is valid. let val_layout = Layout::for_value(unsafe { &*ptr }); // SAFETY: We're computing the layout of a real struct that existed when compiling this @@ -229,8 +229,7 @@ impl<T> Arc<T> { pub fn new(contents: T, flags: Flags) -> Result<Self, AllocError> { // INVARIANT: The refcount is initialised to a non-zero value. let value = ArcInner { - // SAFETY: There are no safety requirements for this FFI call. - refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }), + refcount: Refcount::new(1), data: contents, }; @@ -321,7 +320,7 @@ impl<T: ?Sized> Arc<T> { /// use kernel::sync::{Arc, UniqueArc}; /// /// let arc = Arc::new(42, GFP_KERNEL)?; - /// let unique_arc = arc.into_unique_or_drop(); + /// let unique_arc = Arc::into_unique_or_drop(arc); /// /// // The above conversion should succeed since refcount of `arc` is 1. /// assert!(unique_arc.is_some()); @@ -337,35 +336,30 @@ impl<T: ?Sized> Arc<T> { /// let arc = Arc::new(42, GFP_KERNEL)?; /// let another = arc.clone(); /// - /// let unique_arc = arc.into_unique_or_drop(); + /// let unique_arc = Arc::into_unique_or_drop(arc); /// /// // The above conversion should fail since refcount of `arc` is >1. /// assert!(unique_arc.is_none()); /// /// # Ok::<(), Error>(()) /// ``` - pub fn into_unique_or_drop(self) -> Option<Pin<UniqueArc<T>>> { + pub fn into_unique_or_drop(this: Self) -> Option<Pin<UniqueArc<T>>> { // We will manually manage the refcount in this method, so we disable the destructor. - let me = ManuallyDrop::new(self); + let this = ManuallyDrop::new(this); // SAFETY: We own a refcount, so the pointer is still valid. - let refcount = unsafe { me.ptr.as_ref() }.refcount.get(); + let refcount = unsafe { &this.ptr.as_ref().refcount }; // If the refcount reaches a non-zero value, then we have destroyed this `Arc` and will // return without further touching the `Arc`. If the refcount reaches zero, then there are // no other arcs, and we can create a `UniqueArc`. - // - // SAFETY: We own a refcount, so the pointer is not dangling. - let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) }; - if is_zero { - // SAFETY: We have exclusive access to the arc, so we can perform unsynchronized - // accesses to the refcount. - unsafe { core::ptr::write(refcount, bindings::REFCOUNT_INIT(1)) }; + if refcount.dec_and_test() { + refcount.set(1); // INVARIANT: We own the only refcount to this arc, so we may create a `UniqueArc`. We // must pin the `UniqueArc` because the values was previously in an `Arc`, and they pin // their values. Some(Pin::from(UniqueArc { - inner: ManuallyDrop::into_inner(me), + inner: ManuallyDrop::into_inner(this), })) } else { None @@ -373,10 +367,10 @@ impl<T: ?Sized> Arc<T> { } } -// SAFETY: The pointer returned by `into_foreign` comes from a well aligned -// pointer to `ArcInner<T>`. +// SAFETY: The pointer returned by `into_foreign` was originally allocated as an +// `KBox<ArcInner<T>>`, so that type is what determines the alignment. unsafe impl<T: 'static> ForeignOwnable for Arc<T> { - const FOREIGN_ALIGN: usize = core::mem::align_of::<ArcInner<T>>(); + const FOREIGN_ALIGN: usize = <KBox<ArcInner<T>> as ForeignOwnable>::FOREIGN_ALIGN; type Borrowed<'a> = ArcBorrow<'a, T>; type BorrowedMut<'a> = Self::Borrowed<'a>; @@ -456,14 +450,10 @@ impl<T: ?Sized> Borrow<T> for Arc<T> { impl<T: ?Sized> Clone for Arc<T> { fn clone(&self) -> Self { - // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is - // safe to dereference it. - let refcount = unsafe { self.ptr.as_ref() }.refcount.get(); - - // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero. + // INVARIANT: `Refcount` saturates the refcount, so it cannot overflow to zero. // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is // safe to increment the refcount. - unsafe { bindings::refcount_inc(refcount) }; + unsafe { self.ptr.as_ref() }.refcount.inc(); // SAFETY: We just incremented the refcount. This increment is now owned by the new `Arc`. unsafe { Self::from_inner(self.ptr) } @@ -472,16 +462,10 @@ impl<T: ?Sized> Clone for Arc<T> { impl<T: ?Sized> Drop for Arc<T> { fn drop(&mut self) { - // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot - // touch `refcount` after it's decremented to a non-zero value because another thread/CPU - // may concurrently decrement it to zero and free it. It is ok to have a raw pointer to - // freed/invalid memory as long as it is never dereferenced. - let refcount = unsafe { self.ptr.as_ref() }.refcount.get(); - // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and // this instance is being dropped, so the broken invariant is not observable. - // SAFETY: Also by the type invariant, we are allowed to decrement the refcount. - let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) }; + // SAFETY: By the type invariant, there is necessarily a reference to the object. + let is_zero = unsafe { self.ptr.as_ref() }.refcount.dec_and_test(); if is_zero { // The count reached zero, we must free the memory. // @@ -775,8 +759,7 @@ impl<T> UniqueArc<T> { // INVARIANT: The refcount is initialised to a non-zero value. let inner = KBox::try_init::<AllocError>( try_init!(ArcInner { - // SAFETY: There are no safety requirements for this FFI call. - refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }), + refcount: Refcount::new(1), data <- pin_init::uninit::<T, AllocError>(), }? AllocError), flags, |