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rust: init: add PinnedDrop trait and macros

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The `PinnedDrop` trait that facilitates destruction of pinned types.
It has to be implemented via the `#[pinned_drop]` macro, since the
`drop` function should not be called by normal code, only by other
destructors. It also only works on structs that are annotated with
`#[pin_data(PinnedDrop)]`.

Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-10-y86-dev@protonmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin 2023-04-08 12:26:01 +00:00 committed by Miguel Ojeda
parent 92c4a1e7e8
commit d0fdc39612
5 changed files with 488 additions and 0 deletions
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111
rust/kernel/init.rs
View File

@ -104,6 +104,78 @@
//! }
//! ```
//!
//! ## Manual creation of an initializer
//!
//! Often when working with primitives the previous approaches are not sufficient. That is where
//! [`pin_init_from_closure()`] comes in. This `unsafe` function allows you to create a
//! [`impl PinInit<T, E>`] directly from a closure. Of course you have to ensure that the closure
//! actually does the initialization in the correct way. Here are the things to look out for
//! (we are calling the parameter to the closure `slot`):
//! - when the closure returns `Ok(())`, then it has completed the initialization successfully, so
//! `slot` now contains a valid bit pattern for the type `T`,
//! - when the closure returns `Err(e)`, then the caller may deallocate the memory at `slot`, so
//! you need to take care to clean up anything if your initialization fails mid-way,
//! - you may assume that `slot` will stay pinned even after the closure returns until `drop` of
//! `slot` gets called.
//!
//! ```rust
//! use kernel::{prelude::*, init};
//! use core::{ptr::addr_of_mut, marker::PhantomPinned, pin::Pin};
//! # mod bindings {
//! # pub struct foo;
//! # pub unsafe fn init_foo(_ptr: *mut foo) {}
//! # pub unsafe fn destroy_foo(_ptr: *mut foo) {}
//! # pub unsafe fn enable_foo(_ptr: *mut foo, _flags: u32) -> i32 { 0 }
//! # }
//! /// # Invariants
//! ///
//! /// `foo` is always initialized
//! #[pin_data(PinnedDrop)]
//! pub struct RawFoo {
//! #[pin]
//! foo: Opaque<bindings::foo>,
//! #[pin]
//! _p: PhantomPinned,
//! }
//!
//! impl RawFoo {
//! pub fn new(flags: u32) -> impl PinInit<Self, Error> {
//! // SAFETY:
//! // - when the closure returns `Ok(())`, then it has successfully initialized and
//! // enabled `foo`,
//! // - when it returns `Err(e)`, then it has cleaned up before
//! unsafe {
//! init::pin_init_from_closure(move |slot: *mut Self| {
//! // `slot` contains uninit memory, avoid creating a reference.
//! let foo = addr_of_mut!((*slot).foo);
//!
//! // Initialize the `foo`
//! bindings::init_foo(Opaque::raw_get(foo));
//!
//! // Try to enable it.
//! let err = bindings::enable_foo(Opaque::raw_get(foo), flags);
//! if err != 0 {
//! // Enabling has failed, first clean up the foo and then return the error.
//! bindings::destroy_foo(Opaque::raw_get(foo));
//! return Err(Error::from_kernel_errno(err));
//! }
//!
//! // All fields of `RawFoo` have been initialized, since `_p` is a ZST.
//! Ok(())
//! })
//! }
//! }
//! }
//!
//! #[pinned_drop]
//! impl PinnedDrop for RawFoo {
//! fn drop(self: Pin<&mut Self>) {
//! // SAFETY: Since `foo` is initialized, destroying is safe.
//! unsafe { bindings::destroy_foo(self.foo.get()) };
//! }
//! }
//! ```
//!
//! [`sync`]: kernel::sync
//! [pinning]: https://doc.rust-lang.org/std/pin/index.html
//! [structurally pinned fields]:
@ -1084,3 +1156,42 @@ fn try_init<E>(init: impl Init<T, E>) -> Result<Self, E>
Ok(unsafe { this.assume_init() })
}
}
/// Trait facilitating pinned destruction.
///
/// Use [`pinned_drop`] to implement this trait safely:
///
/// ```rust
/// # use kernel::sync::Mutex;
/// use kernel::macros::pinned_drop;
/// use core::pin::Pin;
/// #[pin_data(PinnedDrop)]
/// struct Foo {
/// #[pin]
/// mtx: Mutex<usize>,
/// }
///
/// #[pinned_drop]
/// impl PinnedDrop for Foo {
/// fn drop(self: Pin<&mut Self>) {
/// pr_info!("Foo is being dropped!");
/// }
/// }
/// ```
///
/// # Safety
///
/// This trait must be implemented via the [`pinned_drop`] proc-macro attribute on the impl.
///
/// [`pinned_drop`]: kernel::macros::pinned_drop
pub unsafe trait PinnedDrop: __internal::HasPinData {
/// Executes the pinned destructor of this type.
///
/// While this function is marked safe, it is actually unsafe to call it manually. For this
/// reason it takes an additional parameter. This type can only be constructed by `unsafe` code
/// and thus prevents this function from being called where it should not.
///
/// This extra parameter will be generated by the `#[pinned_drop]` proc-macro attribute
/// automatically.
fn drop(self: Pin<&mut Self>, only_call_from_drop: __internal::OnlyCallFromDrop);
}

15
rust/kernel/init/__internal.rs
View File

@ -161,3 +161,18 @@ fn drop(&mut self) {
}
}
}
/// Token used by `PinnedDrop` to prevent calling the function without creating this unsafely
/// created struct. This is needed, because the `drop` function is safe, but should not be called
/// manually.
pub struct OnlyCallFromDrop(());
impl OnlyCallFromDrop {
/// # Safety
///
/// This function should only be called from the [`Drop::drop`] function and only be used to
/// delegate the destruction to the pinned destructor [`PinnedDrop::drop`] of the same type.
pub unsafe fn new() -> Self {
Self(())
}
}

264
rust/kernel/init/macros.rs
View File

@ -31,6 +31,26 @@
//! pin_init!(Self { t, x: 0 })
//! }
//! }
//!
//! #[pin_data(PinnedDrop)]
//! struct Foo {
//! a: usize,
//! #[pin]
//! b: Bar<u32>,
//! }
//!
//! #[pinned_drop]
//! impl PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>) {
//! println!("{self:p} is getting dropped.");
//! }
//! }
//!
//! let a = 42;
//! let initializer = pin_init!(Foo {
//! a,
//! b <- Bar::new(36),
//! });
//! ```
//!
//! This example includes the most common and important features of the pin-init API.
@ -155,6 +175,14 @@
//! #[allow(drop_bounds)]
//! impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
//! impl<T> MustNotImplDrop for Bar<T> {}
//! // Here comes a convenience check, if one implemented `PinnedDrop`, but forgot to add it to
//! // `#[pin_data]`, then this will error with the same mechanic as above, this is not needed
//! // for safety, but a good sanity check, since no normal code calls `PinnedDrop::drop`.
//! #[allow(non_camel_case_types)]
//! trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
//! impl<T: ::kernel::init::PinnedDrop>
//! UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
//! impl<T> UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for Bar<T> {}
//! };
//! ```
//!
@ -265,6 +293,210 @@
//! }
//! }
//! ```
//!
//! ## `#[pin_data]` on `Foo`
//!
//! Since we already took a look at `#[pin_data]` on `Bar`, this section will only explain the
//! differences/new things in the expansion of the `Foo` definition:
//!
//! ```rust
//! #[pin_data(PinnedDrop)]
//! struct Foo {
//! a: usize,
//! #[pin]
//! b: Bar<u32>,
//! }
//! ```
//!
//! This expands to the following code:
//!
//! ```rust
//! struct Foo {
//! a: usize,
//! b: Bar<u32>,
//! }
//! const _: () = {
//! struct __ThePinData {
//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
//! }
//! impl ::core::clone::Clone for __ThePinData {
//! fn clone(&self) -> Self {
//! *self
//! }
//! }
//! impl ::core::marker::Copy for __ThePinData {}
//! #[allow(dead_code)]
//! impl __ThePinData {
//! unsafe fn b<E>(
//! self,
//! slot: *mut Bar<u32>,
//! // Note that this is `PinInit` instead of `Init`, this is because `b` is
//! // structurally pinned, as marked by the `#[pin]` attribute.
//! init: impl ::kernel::init::PinInit<Bar<u32>, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::PinInit::__pinned_init(init, slot) }
//! }
//! unsafe fn a<E>(
//! self,
//! slot: *mut usize,
//! init: impl ::kernel::init::Init<usize, E>,
//! ) -> ::core::result::Result<(), E> {
//! unsafe { ::kernel::init::Init::__init(init, slot) }
//! }
//! }
//! unsafe impl ::kernel::init::__internal::HasPinData for Foo {
//! type PinData = __ThePinData;
//! unsafe fn __pin_data() -> Self::PinData {
//! __ThePinData {
//! __phantom: ::core::marker::PhantomData,
//! }
//! }
//! }
//! unsafe impl ::kernel::init::__internal::PinData for __ThePinData {
//! type Datee = Foo;
//! }
//! #[allow(dead_code)]
//! struct __Unpin<'__pin> {
//! __phantom_pin: ::core::marker::PhantomData<fn(&'__pin ()) -> &'__pin ()>,
//! __phantom: ::core::marker::PhantomData<fn(Foo) -> Foo>,
//! // Since this field is `#[pin]`, it is listed here.
//! b: Bar<u32>,
//! }
//! #[doc(hidden)]
//! impl<'__pin> ::core::marker::Unpin for Foo where __Unpin<'__pin>: ::core::marker::Unpin {}
//! // Since we specified `PinnedDrop` as the argument to `#[pin_data]`, we expect `Foo` to
//! // implement `PinnedDrop`. Thus we do not need to prevent `Drop` implementations like
//! // before, instead we implement it here and delegate to `PinnedDrop`.
//! impl ::core::ops::Drop for Foo {
//! fn drop(&mut self) {
//! // Since we are getting dropped, no one else has a reference to `self` and thus we
//! // can assume that we never move.
//! let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
//! // Create the unsafe token that proves that we are inside of a destructor, this
//! // type is only allowed to be created in a destructor.
//! let token = unsafe { ::kernel::init::__internal::OnlyCallFromDrop::new() };
//! ::kernel::init::PinnedDrop::drop(pinned, token);
//! }
//! }
//! };
//! ```
//!
//! ## `#[pinned_drop]` on `impl PinnedDrop for Foo`
//!
//! This macro is used to implement the `PinnedDrop` trait, since that trait is `unsafe` and has an
//! extra parameter that should not be used at all. The macro hides that parameter.
//!
//! Here is the `PinnedDrop` impl for `Foo`:
//!
//! ```rust
//! #[pinned_drop]
//! impl PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>) {
//! println!("{self:p} is getting dropped.");
//! }
//! }
//! ```
//!
//! This expands to the following code:
//!
//! ```rust
//! // `unsafe`, full path and the token parameter are added, everything else stays the same.
//! unsafe impl ::kernel::init::PinnedDrop for Foo {
//! fn drop(self: Pin<&mut Self>, _: ::kernel::init::__internal::OnlyCallFromDrop) {
//! println!("{self:p} is getting dropped.");
//! }
//! }
//! ```
//!
//! ## `pin_init!` on `Foo`
//!
//! Since we already took a look at `pin_init!` on `Bar`, this section will only explain the
//! differences/new things in the expansion of `pin_init!` on `Foo`:
//!
//! ```rust
//! let a = 42;
//! let initializer = pin_init!(Foo {
//! a,
//! b <- Bar::new(36),
//! });
//! ```
//!
//! This expands to the following code:
//!
//! ```rust
//! let a = 42;
//! let initializer = {
//! struct __InitOk;
//! let data = unsafe {
//! use ::kernel::init::__internal::HasPinData;
//! Foo::__pin_data()
//! };
//! let init = ::kernel::init::__internal::PinData::make_closure::<
//! _,
//! __InitOk,
//! ::core::convert::Infallible,
//! >(data, move |slot| {
//! {
//! struct __InitOk;
//! unsafe { ::core::ptr::write(&raw mut (*slot).a, a) };
//! let a = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).a) };
//! let b = Bar::new(36);
//! // Here we use `data` to access the correct field and require that `b` is of type
//! // `PinInit<Bar<u32>, Infallible>`.
//! unsafe { data.b(&raw mut (*slot).b, b)? };
//! let b = &unsafe { ::kernel::init::__internal::DropGuard::new(&raw mut (*slot).b) };
//!
//! #[allow(unreachable_code, clippy::diverging_sub_expression)]
//! if false {
//! unsafe {
//! ::core::ptr::write(
//! slot,
//! Foo {
//! a: ::core::panic!(),
//! b: ::core::panic!(),
//! },
//! );
//! };
//! }
//! unsafe { ::kernel::init::__internal::DropGuard::forget(a) };
//! unsafe { ::kernel::init::__internal::DropGuard::forget(b) };
//! }
//! Ok(__InitOk)
//! });
//! let init = move |slot| -> ::core::result::Result<(), ::core::convert::Infallible> {
//! init(slot).map(|__InitOk| ())
//! };
//! let init = unsafe {
//! ::kernel::init::pin_init_from_closure::<_, ::core::convert::Infallible>(init)
//! };
//! init
//! };
//! ```
/// Creates a `unsafe impl<...> PinnedDrop for $type` block.
///
/// See [`PinnedDrop`] for more information.
#[doc(hidden)]
#[macro_export]
macro_rules! __pinned_drop {
(
@impl_sig($($impl_sig:tt)*),
@impl_body(
$(#[$($attr:tt)*])*
fn drop($($sig:tt)*) {
$($inner:tt)*
}
),
) => {
unsafe $($impl_sig)* {
// Inherit all attributes and the type/ident tokens for the signature.
$(#[$($attr)*])*
fn drop($($sig)*, _: $crate::init::__internal::OnlyCallFromDrop) {
$($inner)*
}
}
}
}
/// This macro first parses the struct definition such that it separates pinned and not pinned
/// fields. Afterwards it declares the struct and implement the `PinData` trait safely.
@ -653,6 +885,38 @@ trait MustNotImplDrop {}
impl<T: ::core::ops::Drop> MustNotImplDrop for T {}
impl<$($impl_generics)*> MustNotImplDrop for $name<$($ty_generics)*>
where $($whr)* {}
// We also take care to prevent users from writing a useless `PinnedDrop` implementation.
// They might implement `PinnedDrop` correctly for the struct, but forget to give
// `PinnedDrop` as the parameter to `#[pin_data]`.
#[allow(non_camel_case_types)]
trait UselessPinnedDropImpl_you_need_to_specify_PinnedDrop {}
impl<T: $crate::init::PinnedDrop>
UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for T {}
impl<$($impl_generics)*>
UselessPinnedDropImpl_you_need_to_specify_PinnedDrop for $name<$($ty_generics)*>
where $($whr)* {}
};
// When `PinnedDrop` was specified we just implement `Drop` and delegate.
(drop_prevention:
@name($name:ident),
@impl_generics($($impl_generics:tt)*),
@ty_generics($($ty_generics:tt)*),
@where($($whr:tt)*),
@pinned_drop(PinnedDrop),
) => {
impl<$($impl_generics)*> ::core::ops::Drop for $name<$($ty_generics)*>
where $($whr)*
{
fn drop(&mut self) {
// SAFETY: Since this is a destructor, `self` will not move after this function
// terminates, since it is inaccessible.
let pinned = unsafe { ::core::pin::Pin::new_unchecked(self) };
// SAFETY: Since this is a drop function, we can create this token to call the
// pinned destructor of this type.
let token = unsafe { $crate::init::__internal::OnlyCallFromDrop::new() };
$crate::init::PinnedDrop::drop(pinned, token);
}
}
};
// If some other parameter was specified, we emit a readable error.
(drop_prevention:

49
rust/macros/lib.rs
View File

@ -8,6 +8,7 @@
mod helpers;
mod module;
mod pin_data;
mod pinned_drop;
mod vtable;
use proc_macro::TokenStream;
@ -180,6 +181,10 @@ pub fn concat_idents(ts: TokenStream) -> TokenStream {
/// This macro enables the use of the [`pin_init!`] macro. When pin-initializing a `struct`,
/// then `#[pin]` directs the type of initializer that is required.
///
/// If your `struct` implements `Drop`, then you need to add `PinnedDrop` as arguments to this
/// macro, and change your `Drop` implementation to `PinnedDrop` annotated with
/// `#[`[`macro@pinned_drop`]`]`, since dropping pinned values requires extra care.
///
/// # Examples
///
/// ```rust,ignore
@ -191,9 +196,53 @@ pub fn concat_idents(ts: TokenStream) -> TokenStream {
/// }
/// ```
///
/// ```rust,ignore
/// #[pin_data(PinnedDrop)]
/// struct DriverData {
/// #[pin]
/// queue: Mutex<Vec<Command>>,
/// buf: Box<[u8; 1024 * 1024]>,
/// raw_info: *mut Info,
/// }
///
/// #[pinned_drop]
/// impl PinnedDrop for DriverData {
/// fn drop(self: Pin<&mut Self>) {
/// unsafe { bindings::destroy_info(self.raw_info) };
/// }
/// }
/// ```
///
/// [`pin_init!`]: ../kernel/macro.pin_init.html
// ^ cannot use direct link, since `kernel` is not a dependency of `macros`.
#[proc_macro_attribute]
pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
pin_data::pin_data(inner, item)
}
/// Used to implement `PinnedDrop` safely.
///
/// Only works on structs that are annotated via `#[`[`macro@pin_data`]`]`.
///
/// # Examples
///
/// ```rust,ignore
/// #[pin_data(PinnedDrop)]
/// struct DriverData {
/// #[pin]
/// queue: Mutex<Vec<Command>>,
/// buf: Box<[u8; 1024 * 1024]>,
/// raw_info: *mut Info,
/// }
///
/// #[pinned_drop]
/// impl PinnedDrop for DriverData {
/// fn drop(self: Pin<&mut Self>) {
/// unsafe { bindings::destroy_info(self.raw_info) };
/// }
/// }
/// ```
#[proc_macro_attribute]
pub fn pinned_drop(args: TokenStream, input: TokenStream) -> TokenStream {
pinned_drop::pinned_drop(args, input)
}

49
rust/macros/pinned_drop.rs Normal file
View File

@ -0,0 +1,49 @@
// SPDX-License-Identifier: Apache-2.0 OR MIT
use proc_macro::{TokenStream, TokenTree};
pub(crate) fn pinned_drop(_args: TokenStream, input: TokenStream) -> TokenStream {
let mut toks = input.into_iter().collect::<Vec<_>>();
assert!(!toks.is_empty());
// Ensure that we have an `impl` item.
assert!(matches!(&toks[0], TokenTree::Ident(i) if i.to_string() == "impl"));
// Ensure that we are implementing `PinnedDrop`.
let mut nesting: usize = 0;
let mut pinned_drop_idx = None;
for (i, tt) in toks.iter().enumerate() {
match tt {
TokenTree::Punct(p) if p.as_char() == '<' => {
nesting += 1;
}
TokenTree::Punct(p) if p.as_char() == '>' => {
nesting = nesting.checked_sub(1).unwrap();
continue;
}
_ => {}
}
if i >= 1 && nesting == 0 {
// Found the end of the generics, this should be `PinnedDrop`.
assert!(
matches!(tt, TokenTree::Ident(i) if i.to_string() == "PinnedDrop"),
"expected 'PinnedDrop', found: '{:?}'",
tt
);
pinned_drop_idx = Some(i);
break;
}
}
let idx = pinned_drop_idx
.unwrap_or_else(|| panic!("Expected an `impl` block implementing `PinnedDrop`."));
// Fully qualify the `PinnedDrop`, as to avoid any tampering.
toks.splice(idx..idx, quote!(::kernel::init::));
// Take the `{}` body and call the declarative macro.
if let Some(TokenTree::Group(last)) = toks.pop() {
let last = last.stream();
quote!(::kernel::__pinned_drop! {
@impl_sig(#(#toks)*),
@impl_body(#last),
})
} else {
TokenStream::from_iter(toks)
}
}