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rust: sync: reduce stack usage of UniqueArc::try_new_uninit

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`UniqueArc::try_new_uninit` calls `Arc::try_new(MaybeUninit::uninit())`.
This results in the uninitialized memory being placed on the stack,
which may be arbitrarily large due to the generic `T` and thus could
cause a stack overflow for large types.

Change the implementation to use the pin-init API which enables in-place
initialization. In particular it avoids having to first construct and
then move the uninitialized memory from the stack into the final location.

Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Andreas Hindborg <a.hindborg@samsung.com>
Link: https://lore.kernel.org/r/20230408122429.1103522-15-y86-dev@protonmail.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Benno Lossin 2023-04-08 12:26:27 +00:00 committed by Miguel Ojeda
parent 692e8935e2
commit 701608bd03
2 changed files with 13 additions and 4 deletions
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1
rust/kernel/lib.rs
View File

@ -28,7 +28,6 @@
#[cfg(not(CONFIG_RUST))]
compile_error!("Missing kernel configuration for conditional compilation");
#[allow(unused_extern_crates)]
// Allow proc-macros to refer to `::kernel` inside the `kernel` crate (this crate).
extern crate self as kernel;

16
rust/kernel/sync/arc.rs
View File

@ -18,7 +18,8 @@
use crate::{
bindings,
error::{self, Error},
init::{InPlaceInit, Init, PinInit},
init::{self, InPlaceInit, Init, PinInit},
try_init,
types::{ForeignOwnable, Opaque},
};
use alloc::boxed::Box;
@ -31,6 +32,7 @@ use core::{
pin::Pin,
ptr::NonNull,
};
use macros::pin_data;
mod std_vendor;
@ -125,6 +127,7 @@ pub struct Arc<T: ?Sized> {
_p: PhantomData<ArcInner<T>>,
}
#[pin_data]
#[repr(C)]
struct ArcInner<T: ?Sized> {
refcount: Opaque<bindings::refcount_t>,
@ -505,9 +508,16 @@ impl<T> UniqueArc<T> {
/// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
pub fn try_new_uninit() -> Result<UniqueArc<MaybeUninit<T>>, AllocError> {
Ok(UniqueArc::<MaybeUninit<T>> {
// INVARIANT: The refcount is initialised to a non-zero value.
let inner = Box::try_init::<AllocError>(try_init!(ArcInner {
// SAFETY: There are no safety requirements for this FFI call.
refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
data <- init::uninit::<T, AllocError>(),
}? AllocError))?;
Ok(UniqueArc {
// INVARIANT: The newly-created object has a ref-count of 1.
inner: Arc::try_new(MaybeUninit::uninit())?,
// SAFETY: The pointer from the `Box` is valid.
inner: unsafe { Arc::from_inner(Box::leak(inner).into()) },
})
}
}