Messages in this thread | | | From | Andreas Hindborg <> | Subject | Re: [PATCH v1 6/7] rust: workqueue: add safe API to workqueue | Date | Tue, 30 May 2023 10:51:14 +0200 |
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Alice Ryhl <aliceryhl@google.com> writes:
> This commit introduces `ArcWorkItem`, `BoxWorkItem`, and > `define_work_adapter_newtype!` that make it possible to use the > workqueue without any unsafe code whatsoever. > > The `ArcWorkItem` and `BoxWorkItem` traits are used when a struct has a > single `work_struct` field. > > The `define_work_adapter_newtype!` macro is used when a struct has > multiple `work_struct` fields. For each `work_struct` field, a newtype > struct is defined that wraps `Arc<TheStruct>`, and pushing an instance > of the newtype to a workqueue will enqueue it using the associated > `work_struct` field. The newtypes are matched with `work_struct` fields > by having the T in `Work<T>` be the newtype. > > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > rust/kernel/workqueue.rs | 332 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 331 insertions(+), 1 deletion(-) > > diff --git a/rust/kernel/workqueue.rs b/rust/kernel/workqueue.rs > index 7509618af252..007005ddcaf0 100644 > --- a/rust/kernel/workqueue.rs > +++ b/rust/kernel/workqueue.rs > @@ -4,8 +4,9 @@ > //! > //! C header: [`include/linux/workqueue.h`](../../../../include/linux/workqueue.h) > > -use crate::{bindings, prelude::*, types::Opaque}; > +use crate::{bindings, prelude::*, sync::Arc, types::Opaque}; > use core::marker::{PhantomData, PhantomPinned}; > +use core::result::Result; > > /// A kernel work queue. > /// > @@ -279,6 +280,335 @@ macro_rules! impl_has_work { > )*}; > } > > +/// Declares that [`Arc<Self>`] should implement [`WorkItem`]. > +/// > +/// # Examples > +/// > +/// The example below will make [`Arc<MyStruct>`] implement the [`WorkItem`] trait so that you can > +/// enqueue it in a workqueue. > +/// > +/// ``` > +/// use kernel::sync::Arc; > +/// > +/// struct MyStruct { > +/// work_field: Work<Arc<MyStruct>>, > +/// } > +/// > +/// kernel::impl_has_work! { > +/// impl HasWork<Arc<MyStruct>> for MyStruct { self.work_field } > +/// } > +/// > +/// impl ArcWorkItem for MyStruct { > +/// fn run(self: Arc<Self>) { > +/// pr_info!("Executing MyStruct on a workqueue."); > +/// } > +/// } > +/// ``` > +/// > +/// [`Arc<Self>`]: crate::sync::Arc > +/// [`Arc<MyStruct>`]: crate::sync::Arc > +pub trait ArcWorkItem { > + /// Called when this work item is executed. > + fn run(self: Arc<Self>); > +} > + > +unsafe impl<T> WorkItem for Arc<T> > +where > + T: ArcWorkItem + HasWork<Self> + ?Sized, > +{ > + type EnqueueOutput = Result<(), Self>; > + > + unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput > + where > + F: FnOnce(*mut bindings::work_struct) -> bool, > + { > + let ptr = Arc::into_raw(self); > + > + // Using `get_work_offset` here for object-safety. > + // > + // SAFETY: The pointer is valid since we just got it from `into_raw`. > + let off = unsafe { (&*ptr).get_work_offset() }; > + > + // SAFETY: The `HasWork` impl promises that this offset gives us a field of type > + // `Work<Self>` in the same allocation. > + let work_ptr = unsafe { (ptr as *const u8).add(off) as *const Work<Self> };
We have this functionality in the default impl of `HasWork<T>::raw_get_work() where Self: Sized`. I am uncertain about the `Sized` bound. If it is sound to do the offset calculation here where `T: ?Sized`, it should also be sound in the default implementation of `HasWork<T>`. Should we not be able to change the bound on `HasWork<T>::raw_get_work()` to `Self: ?Sized` and call into that from here?
let work_ptr = unsafe { <T as HasWork<Self>>::raw_get_work(ptr as _) };
Same for Box.
BR Andreas
> + // SAFETY: The pointer is not dangling. > + let work_ptr = unsafe { Work::raw_get(work_ptr) }; > + > + match (queue_work_on)(work_ptr) { > + true => Ok(()), > + // SAFETY: The work queue has not taken ownership of the pointer. > + false => Err(unsafe { Arc::from_raw(ptr) }), > + } > + } > +} > + > +// Let `Work<Arc<T>>` be usable with types that are `ArcWorkItem`. > +// > +// We do not allow unsized types here. The `Work<Arc<T>>` field should always specify the actual > +// concrete type stored in the `Arc`. > +// > +// SAFETY: The `Work<Arc<T>>` field must be initialized with this `run` method because the `Work` > +// struct prevents you from initializing it in any other way. The `__enqueue` trait uses the > +// same `Work<Arc<T>>` field because `HasWork` promises to always return the same field. > +unsafe impl<T> WorkItemAdapter for Arc<T> > +where > + T: ArcWorkItem + HasWork<Self> + Sized, > +{ > + unsafe extern "C" fn run(ptr: *mut bindings::work_struct) { > + // SAFETY: The `__enqueue` method always uses a `work_struct` stored in a `Work<Self>`. > + let ptr = ptr as *mut Work<Self>; > + // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`. > + let ptr = unsafe { T::work_container_of(ptr) }; > + // SAFETY: This pointer comes from `Arc::into_raw` and we've been given back ownership. > + let arc = unsafe { Arc::from_raw(ptr) }; > + > + arc.run(); > + } > +} > + > +/// Declares that [`Pin`]`<`[`Box`]`<Self>>` should implement [`WorkItem`]. > +/// > +/// # Examples > +/// > +/// The example below will make [`Pin`]`<`[`Box`]`<MyStruct>>` implement the [`WorkItem`] trait so > +/// that you can enqueue it in a workqueue. > +/// > +/// ``` > +/// struct MyStruct { > +/// work_field: Work<Pin<Box<MyStruct>>>, > +/// } > +/// > +/// kernel::impl_has_work! { > +/// impl HasWork<Pin<Box<MyStruct>>> for MyStruct { self.work_field } > +/// } > +/// > +/// impl BoxWorkItem for MyStruct { > +/// fn run(self: Pin<Box<MyStruct>>) { > +/// pr_info!("Executing MyStruct on a workqueue."); > +/// } > +/// } > +/// ``` > +/// > +/// [`Box`]: alloc::boxed::Box > +/// [`Pin`]: core::pin::Pin > +pub trait BoxWorkItem { > + /// Called when this work item is executed. > + fn run(self: Pin<Box<Self>>); > +} > + > +unsafe impl<T> WorkItem for Pin<Box<T>> > +where > + T: BoxWorkItem + HasWork<Self> + ?Sized, > +{ > + // When a box is in a workqueue, the workqueue has exclusive ownership of the box. Therefore, > + // it's not possible to enqueue a box while it is in a workqueue. > + type EnqueueOutput = (); > + > + unsafe fn __enqueue<F>(self, queue_work_on: F) > + where > + F: FnOnce(*mut bindings::work_struct) -> bool, > + { > + // SAFETY: We will not used the contents in an unpinned manner. > + let ptr = unsafe { Box::into_raw(Pin::into_inner_unchecked(self)) }; > + > + // Using `get_work_offset` here for object-safety. > + // > + // SAFETY: The pointer is valid since we just got it from `into_raw`. > + let off = unsafe { (&*ptr).get_work_offset() }; > + > + // SAFETY: The `HasWork` impl promises that this offset gives us a field of type > + // `Work<Self>` in the same allocation. > + let work_ptr = unsafe { (ptr as *mut u8).add(off) as *mut Work<Self> }; > + // SAFETY: The pointer is not dangling. > + let work_ptr = unsafe { Work::raw_get(work_ptr) }; > + > + match (queue_work_on)(work_ptr) { > + true => {} > + // SAFETY: This method requires exclusive ownership of the box, so it cannot be in a > + // workqueue. > + false => unsafe { core::hint::unreachable_unchecked() }, > + } > + } > +} > + > +// Let `Work<Pin<Box<T>>>` be usable with types that are `BoxWorkItem`. > +// > +// We do not allow unsized types here. The `Work<Pin<Box<T>>>` field should always specify the actual > +// concrete type stored in the `Box`. > +// > +// SAFETY: The `Work<Pin<Box<T>>>` field must be initialized with this run method because the `Work` > +// struct prevents you from initializing it in any other way. The `__enqueue` trait uses the > +// same `Work<Pin<Box<T>>>` field because `HasWork` promises to always return the same field. > +unsafe impl<T> WorkItemAdapter for Pin<Box<T>> > +where > + T: BoxWorkItem + HasWork<Self> + Sized, > +{ > + unsafe extern "C" fn run(ptr: *mut bindings::work_struct) { > + // SAFETY: The `__enqueue` method always uses a `work_struct` stored in a `Work<Self>`. > + let ptr = ptr as *mut Work<Self>; > + // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`. > + let ptr = unsafe { T::work_container_of(ptr) }; > + // SAFETY: This pointer comes from `Box::into_raw` and we've been given back ownership. > + // The box was originally pinned, so pinning it again is ok. > + let boxed = unsafe { Pin::new_unchecked(Box::from_raw(ptr)) }; > + > + boxed.run(); > + } > +} > + > +/// Helper macro for structs with several `Work` fields that can be in several queues at once. > +/// > +/// For each `Work` field in your type `T`, a newtype struct that wraps an `Arc<T>` or > +/// `Pin<Box<T>>` should be defined. > +/// > +/// # Examples > +/// > +/// ``` > +/// struct MyStruct { > +/// work1: Work<MyStructWork1>, > +/// work2: Work<MyStructWork2>, > +/// } > +/// > +/// impl_has_work! { > +/// impl HasWork<MyStructWork1> for MyStruct { self.work1 } > +/// impl HasWork<MyStructWork2> for MyStruct { self.work2 } > +/// } > +/// > +/// define_work_adapter_newtype! { > +/// struct MyStructWork1(Arc<MyStruct>); > +/// struct MyStructWork2(Arc<MyStruct>); > +/// } > +/// > +/// impl MyStructWork1 { > +/// fn run(self) { > +/// // ... > +/// } > +/// } > +/// > +/// impl MyStructWork2 { > +/// fn run(self) { > +/// // ... > +/// } > +/// } > +/// ``` > +/// > +/// This will let you push a `MyStructWork1(arc)` or `MyStructWork2(arc)` to a work queue. The [`Arc`] > +/// can be in two work queues at the same time, and the `run` method on the wrapper type is called > +/// when the work item is called. > +/// > +/// [`Arc`]: crate::sync::Arc > +#[macro_export] > +macro_rules! define_work_adapter_newtype { > + ( > + $(#[$outer:meta])* > + $pub:vis struct $name:ident( > + $(#[$innermeta:meta])* > + $fpub:vis Arc<$inner:ty> $(,)? > + ); > + $($rest:tt)* > + ) => { > + $(#[$outer])* > + $pub struct $name($(#[$innermeta])* $fpub $crate::sync::Arc<$inner>); > + > + unsafe impl $crate::workqueue::WorkItem for $name { > + type EnqueueOutput = ::core::result::Result<(), $name>; > + > + unsafe fn __enqueue<F>(self, queue_work_on: F) -> Self::EnqueueOutput > + where > + F: ::core::ops::FnOnce(*mut $crate::bindings::work_struct) -> bool, > + { > + let ptr = $crate::sync::Arc::into_raw(self.0); > + > + // SAFETY: The pointer is not dangling since we just got it from Arc::into_raw. > + let work_ptr = unsafe { <$inner as $crate::workqueue::HasWork::<$name>>::raw_get_work(ptr.cast_mut()) }; > + > + // SAFETY: The pointer is not dangling. > + let work_ptr = unsafe { $crate::workqueue::Work::raw_get(work_ptr) }; > + > + match (queue_work_on)(work_ptr) { > + true => Ok(()), > + // SAFETY: The work queue has not taken ownership of the pointer. > + false => Err($name(unsafe { $crate::sync::Arc::from_raw(ptr) })), > + } > + } > + } > + > + unsafe impl $crate::workqueue::WorkItemAdapter for $name { > + unsafe extern "C" fn run(ptr: *mut $crate::bindings::work_struct) { > + // SAFETY: The `__enqueue` method always uses a `work_struct` stored in a `Work<Self>`. > + let ptr = ptr as *mut $crate::workqueue::Work<Self>; > + // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`. > + let ptr = unsafe { <$inner as $crate::workqueue::HasWork::<$name>>::work_container_of(ptr) }; > + // SAFETY: This pointer comes from `Arc::into_raw` and we've been given back ownership. > + let arc = unsafe { $crate::sync::Arc::from_raw(ptr) }; > + > + $name::run($name(arc)); > + } > + } > + > + define_work_adapter_newtype! { $($rest)* } > + }; > + > + ( > + $(#[$outer:meta])* > + $pub:vis struct $name:ident( > + $(#[$innermeta:meta])* > + $fpub:vis Pin<Box<$inner:ty>> $(,)? > + ); > + $($rest:tt)* > + ) => { > + $(#[$outer])* > + $pub struct $name($(#[$innermeta])* $fpub ::core::pin::Pin<::alloc::boxed::Box<$inner>>); > + > + unsafe impl $crate::workqueue::WorkItem for $name { > + type EnqueueOutput = (); > + > + unsafe fn __enqueue<F>(self, queue_work_on: F) > + where > + F: ::core::ops::FnOnce(*mut $crate::bindings::work_struct) -> bool, > + { > + // SAFETY: We will not used the contents in an unpinned manner. > + let boxed = unsafe { ::core::pin::Pin::into_inner_unchecked(self.0) }; > + let ptr = ::alloc::boxed::Box::into_raw(boxed); > + > + // SAFETY: The pointer is not dangling since we just got it from Box::into_raw. > + let work_ptr = unsafe { <$inner as $crate::workqueue::HasWork::<$name>>::raw_get_work(ptr) }; > + > + // SAFETY: The pointer is not dangling. > + let work_ptr = unsafe { $crate::workqueue::Work::raw_get(work_ptr) }; > + > + match (queue_work_on)(work_ptr) { > + true => {}, > + // SAFETY: This method requires exclusive ownership of the box, so it cannot be in a > + // workqueue. > + false => unsafe { ::core::hint::unreachable_unchecked() }, > + } > + } > + } > + > + unsafe impl $crate::workqueue::WorkItemAdapter for $name { > + unsafe extern "C" fn run(ptr: *mut $crate::bindings::work_struct) { > + // SAFETY: The `__enqueue` method always uses a `work_struct` stored in a `Work<Self>`. > + let ptr = ptr as *mut $crate::workqueue::Work<Self>; > + // SAFETY: This computes the pointer that `__enqueue` got from `Arc::into_raw`. > + let ptr = unsafe { <$inner as $crate::workqueue::HasWork::<$name>>::work_container_of(ptr) }; > + // SAFETY: This pointer comes from `Box::into_raw` and we've been given back ownership. > + let boxed = unsafe { ::alloc::boxed::Box::from_raw(ptr) }; > + // SAFETY: The box was originally pinned, so pinning it again is ok. > + let boxed = unsafe { ::core::pin::Pin::new_unchecked(boxed) }; > + > + $name::run($name(boxed)); > + } > + } > + > + define_work_adapter_newtype! { $($rest)* } > + }; > + > + // After processing the last definition, we call ourselves with no input. > + () => {}; > +} > + > /// Returns the system work queue (`system_wq`). > /// > /// It is the one used by `schedule[_delayed]_work[_on]()`. Multi-CPU multi-threaded. There are
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