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rust: init: make guards in the init macros hygienic

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Use hygienic identifiers for the guards instead of the field names. This
makes the init macros feel more like normal struct initializers, since
assigning identifiers with the name of a field does not create
conflicts.

Also change the internals of the guards, no need to make the `forget`
function `unsafe`, since users cannot access the guards anyways. Now the
guards are carried directly on the stack and have no extra `Cell<bool>`
field that marks if they have been forgotten or not, instead they are
just forgotten via `mem::forget`.

Suggested-by: Asahi Lina <lina@asahilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Link: https://lore.kernel.org/r/20230814084602.25699-5-benno.lossin@proton.me
[ Cleaned a few trivial nits. ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin 2023-08-14 08:46:48 +00:00 committed by Miguel Ojeda
parent 071cedc84e
commit 97de919d57
3 changed files with 56 additions and 86 deletions
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1
rust/kernel/init.rs
View file

@ -206,7 +206,6 @@
use alloc::boxed::Box;
use core::{
alloc::AllocError,
cell::Cell,
convert::Infallible,
marker::PhantomData,
mem::MaybeUninit,

19
rust/kernel/init/__internal.rs
View file

@ -174,7 +174,6 @@ pub fn init<E>(self: Pin<&mut Self>, init: impl PinInit<T, E>) -> Result<Pin<&mu
/// Can be forgotten to prevent the drop.
pub struct DropGuard<T: ?Sized> {
ptr: *mut T,
do_drop: Cell<bool>,
}
impl<T: ?Sized> DropGuard<T> {
@ -190,34 +189,18 @@ impl<T: ?Sized> DropGuard<T> {
/// - will not be dropped by any other means.
#[inline]
pub unsafe fn new(ptr: *mut T) -> Self {
Self {
ptr,
do_drop: Cell::new(true),
}
}
/// Prevents this guard from dropping the supplied pointer.
///
/// # Safety
///
/// This function is unsafe in order to prevent safe code from forgetting this guard. It should
/// only be called by the macros in this module.
#[inline]
pub unsafe fn forget(&self) {
self.do_drop.set(false);
Self { ptr }
}
}
impl<T: ?Sized> Drop for DropGuard<T> {
#[inline]
fn drop(&mut self) {
if self.do_drop.get() {
// SAFETY: A `DropGuard` can only be constructed using the unsafe `new` function
// ensuring that this operation is safe.
unsafe { ptr::drop_in_place(self.ptr) }
}
}
}
/// 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

68
rust/kernel/init/macros.rs
View file

@ -994,7 +994,6 @@ impl<$($impl_generics)*> $pin_data<$($ty_generics)*>
/// - `init_slot`: recursively creates the code that initializes all fields in `slot`.
/// - `make_initializer`: recursively create the struct initializer that guarantees that every
/// field has been initialized exactly once.
/// - `forget_guards`: recursively forget the drop guards for every field.
#[doc(hidden)]
#[macro_export]
macro_rules! __init_internal {
@ -1034,6 +1033,7 @@ macro_rules! __init_internal {
$crate::__init_internal!(init_slot($($use_data)?):
@data(data),
@slot(slot),
@guards(),
@munch_fields($($fields)*,),
);
// We use unreachable code to ensure that all fields have been mentioned exactly
@ -1048,10 +1048,6 @@ macro_rules! __init_internal {
@acc(),
);
}
// Forget all guards, since initialization was a success.
$crate::__init_internal!(forget_guards:
@munch_fields($($fields)*,),
);
}
Ok(__InitOk)
}
@ -1065,13 +1061,17 @@ macro_rules! __init_internal {
(init_slot($($use_data:ident)?):
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
@munch_fields($(,)?),
) => {
// Endpoint of munching, no fields are left.
// Endpoint of munching, no fields are left. If execution reaches this point, all fields
// have been initialized. Therefore we can now dismiss the guards by forgetting them.
$(::core::mem::forget($guards);)*
};
(init_slot($use_data:ident): // `use_data` is present, so we use the `data` to init fields.
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// In-place initialization syntax.
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
) => {
@ -1082,24 +1082,28 @@ macro_rules! __init_internal {
// return when an error/panic occurs.
// We also use the `data` to require the correct trait (`Init` or `PinInit`) for `$field`.
unsafe { $data.$field(::core::ptr::addr_of_mut!((*$slot).$field), $field)? };
// Create the drop guard.
//
// We only give access to `&DropGuard`, so it cannot be forgotten via safe code.
// Create the drop guard:
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let $field = &unsafe {
let [<$field>] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot($use_data):
@data($data),
@slot($slot),
@guards([<$field>], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(init_slot(): // No `use_data`, so we use `Init::__init` directly.
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// In-place initialization syntax.
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
) => {
@ -1109,24 +1113,28 @@ macro_rules! __init_internal {
// SAFETY: `slot` is valid, because we are inside of an initializer closure, we
// return when an error/panic occurs.
unsafe { $crate::init::Init::__init($field, ::core::ptr::addr_of_mut!((*$slot).$field))? };
// Create the drop guard.
//
// We only give access to `&DropGuard`, so it cannot be forgotten via safe code.
// Create the drop guard:
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let $field = &unsafe {
let [<$field>] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot():
@data($data),
@slot($slot),
@guards([<$field>], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(init_slot($($use_data:ident)?):
@data($data:ident),
@slot($slot:ident),
@guards($($guards:ident,)*),
// Init by-value.
@munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
) => {
@ -1137,18 +1145,21 @@ macro_rules! __init_internal {
unsafe { ::core::ptr::write(::core::ptr::addr_of_mut!((*$slot).$field), $field) };
// Create the drop guard:
//
// We only give access to `&DropGuard`, so it cannot be accidentally forgotten.
//
// We rely on macro hygiene to make it impossible for users to access this local variable.
// We use `paste!` to create new hygiene for `$field`.
::kernel::macros::paste! {
// SAFETY: We forget the guard later when initialization has succeeded.
let $field = &unsafe {
let [<$field>] = unsafe {
$crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
};
$crate::__init_internal!(init_slot($($use_data)?):
@data($data),
@slot($slot),
@guards([<$field>], $($guards,)*),
@munch_fields($($rest)*),
);
}
};
(make_initializer:
@slot($slot:ident),
@ -1191,29 +1202,6 @@ macro_rules! __init_internal {
@acc($($acc)* $field: ::core::panic!(),),
);
};
(forget_guards:
@munch_fields($(,)?),
) => {
// Munching finished.
};
(forget_guards:
@munch_fields($field:ident <- $val:expr, $($rest:tt)*),
) => {
unsafe { $crate::init::__internal::DropGuard::forget($field) };
$crate::__init_internal!(forget_guards:
@munch_fields($($rest)*),
);
};
(forget_guards:
@munch_fields($field:ident $(: $val:expr)?, $($rest:tt)*),
) => {
unsafe { $crate::init::__internal::DropGuard::forget($field) };
$crate::__init_internal!(forget_guards:
@munch_fields($($rest)*),
);
};
}
#[doc(hidden)]