* [PATCH v4 14/15] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit`
@ 2023-03-31 21:54 y86-dev
0 siblings, 0 replies; only message in thread
From: y86-dev @ 2023-03-31 21:54 UTC (permalink / raw
To: Miguel Ojeda, Alex Gaynor, Wedson Almeida Filho, Boqun Feng,
Gary Guo, Björn Roy Baron, Alice Ryhl
Cc: rust-for-linux, linux-kernel, patches, Benno Lossin, Alice Ryhl,
Andreas Hindborg
From: Benno Lossin <y86-dev@protonmail.com>
`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>
---
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 24dc96603090..5f64affd8f33 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -17,7 +17,8 @@
use crate::{
bindings,
- init::{InPlaceInit, Init, PinInit},
+ init::{self, InPlaceInit, Init, PinInit},
+ try_init,
types::{ForeignOwnable, Opaque},
};
use alloc::boxed::Box;
@@ -29,6 +30,7 @@ use core::{
pin::Pin,
ptr::NonNull,
};
+use macros::pin_data;
/// A reference-counted pointer to an instance of `T`.
///
@@ -121,6 +123,7 @@ pub struct Arc<T: ?Sized> {
_p: PhantomData<ArcInner<T>>,
}
+#[pin_data]
#[repr(C)]
struct ArcInner<T: ?Sized> {
refcount: Opaque<bindings::refcount_t>,
@@ -501,9 +504,16 @@ 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
^ permalink raw reply related [flat|nested] only message in thread
only message in thread, other threads:[~2023-03-31 21:56 UTC | newest]
Thread overview: (only message) (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2023-03-31 21:54 [PATCH v4 14/15] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` y86-dev
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.