Messages in this thread Patch in this message | | | Date | Tue, 4 Apr 2023 14:25:35 +0100 | From | Gary Guo <> | Subject | Re: [PATCH v5 14/15] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` |
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On Mon, 03 Apr 2023 16:05:56 +0000 Benno Lossin <y86-dev@protonmail.com> wrote:
> `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 <y86-dev@protonmail.com> > Cc: Gary Guo <gary@garyguo.net> > Cc: Alice Ryhl <aliceryhl@google.com> > Cc: Andreas Hindborg <a.hindborg@samsung.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
> --- > rust/kernel/lib.rs | 1 - > rust/kernel/sync/arc.rs | 16 +++++++++++++--- > 2 files changed, 13 insertions(+), 4 deletions(-) > > diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs > index 821bd067151c..2d7606135ef6 100644 > --- a/rust/kernel/lib.rs > +++ b/rust/kernel/lib.rs > @@ -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; > > diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs > index 43a53fbe175d..d05caa723718 100644 > --- a/rust/kernel/sync/arc.rs > +++ b/rust/kernel/sync/arc.rs > @@ -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; > @@ -30,6 +31,7 @@ use core::{ > pin::Pin, > ptr::NonNull, > }; > +use macros::pin_data; > > /// A reference-counted pointer to an instance of `T`. > /// > @@ -122,6 +124,7 @@ pub struct Arc<T: ?Sized> { > _p: PhantomData<ArcInner<T>>, > } > > +#[pin_data] > #[repr(C)] > struct ArcInner<T: ?Sized> { > refcount: Opaque<bindings::refcount_t>, > @@ -502,9 +505,16 @@ 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()) }, > }) > } > } > -- > 2.39.2 > >
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