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Date: Mon, 14 Aug 2023 08:46:48 +0000
From: Benno Lossin <benno.lossin@...ton.me>
To: Miguel Ojeda <ojeda@...nel.org>,
Wedson Almeida Filho <wedsonaf@...il.com>,
Alex Gaynor <alex.gaynor@...il.com>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
Björn Roy Baron <bjorn3_gh@...tonmail.com>,
Benno Lossin <benno.lossin@...ton.me>,
Alice Ryhl <aliceryhl@...gle.com>,
Andreas Hindborg <nmi@...aspace.dk>,
rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org,
patches@...ts.linux.dev, Asahi Lina <lina@...hilina.net>,
Martin Rodriguez Reboredo <yakoyoku@...il.com>
Subject: [PATCH v4 04/13] rust: init: make guards in the init macros hygienic
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@...hilina.net>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@...il.com>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Gary Guo <gary@...yguo.net>
Signed-off-by: Benno Lossin <benno.lossin@...ton.me>
---
v3 -> v4:
- added Reviewed-by from Gary.
v2 -> v3:
- added Reviewed-by's from Martin and Alice.
v1 -> v2:
- use Gary's `paste!` macro to create the guard hygiene.
rust/kernel/init.rs | 1 -
rust/kernel/init/__internal.rs | 25 ++-----
rust/kernel/init/macros.rs | 116 +++++++++++++++------------------
3 files changed, 56 insertions(+), 86 deletions(-)
diff --git a/rust/kernel/init.rs b/rust/kernel/init.rs
index d431d0b153a2..0120674b451e 100644
--- a/rust/kernel/init.rs
+++ b/rust/kernel/init.rs
@@ -216,7 +216,6 @@
use alloc::boxed::Box;
use core::{
alloc::AllocError,
- cell::Cell,
convert::Infallible,
marker::PhantomData,
mem::MaybeUninit,
diff --git a/rust/kernel/init/__internal.rs b/rust/kernel/init/__internal.rs
index 44751fb62b51..7abd1fb65e41 100644
--- a/rust/kernel/init/__internal.rs
+++ b/rust/kernel/init/__internal.rs
@@ -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> {
@@ -190,32 +189,16 @@ 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) }
- }
+ // 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) }
}
}
diff --git a/rust/kernel/init/macros.rs b/rust/kernel/init/macros.rs
index 78091756dec0..454f31b8c614 100644
--- a/rust/kernel/init/macros.rs
+++ b/rust/kernel/init/macros.rs
@@ -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:
//
- // SAFETY: We forget the guard later when initialization has succeeded.
- let $field = &unsafe {
- $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
- };
+ // 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 {
+ $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+ };
- $crate::__init_internal!(init_slot($use_data):
- @data($data),
- @slot($slot),
- @munch_fields($($rest)*),
- );
+ $crate::__init_internal!(init_slot($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:
//
- // SAFETY: We forget the guard later when initialization has succeeded.
- let $field = &unsafe {
- $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
- };
+ // 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 {
+ $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+ };
- $crate::__init_internal!(init_slot():
- @data($data),
- @slot($slot),
- @munch_fields($($rest)*),
- );
+ $crate::__init_internal!(init_slot():
+ @data($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.
- //
- // SAFETY: We forget the guard later when initialization has succeeded.
- let $field = &unsafe {
- $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
- };
+ // 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 {
+ $crate::init::__internal::DropGuard::new(::core::ptr::addr_of_mut!((*$slot).$field))
+ };
- $crate::__init_internal!(init_slot($($use_data)?):
- @data($data),
- @slot($slot),
- @munch_fields($($rest)*),
- );
+ $crate::__init_internal!(init_slot($($use_data)?):
+ @data($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)]
--
2.41.0
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