From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-4322.protonmail.ch (mail-4322.protonmail.ch [185.70.43.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD6FCE4C8 for ; Wed, 29 Mar 2023 22:34:00 +0000 (UTC) Date: Wed, 29 Mar 2023 22:33:49 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=protonmail3; t=1680129238; x=1680388438; bh=sxLceGSRcRRyUDLrAQ3TsPyF0muTqsPNCkcHAqeAS3Y=; h=Date:To:From:Cc:Subject:Message-ID:Feedback-ID:From:To:Cc:Date: Subject:Reply-To:Feedback-ID:Message-ID:BIMI-Selector; b=Zwb1MUx0yFoVE9sf9Mb1tWUXfmh2qVpyjWSLpofWZdfMidwMRgbwK6j4js7H30ZOn blYDhGfDJAyc8p99nIdH+KopD/vrdi+3JUmIDevsR2jEkgvPTq1wDmTlhoEAL1gPgh MQipP6aGvkNdpzcpVvTWmfiCN57Bemt5dm/ayMF7HV5c29RF+ldIsAgWYuQJQSHcO+ QW0HjHotWaWJ3MbboE6J2l3a1dPFzqIiOhfjlCOrJlf9kILO1YsXSVuBIND185TWLU n5qo/ZQzDtNp0RouDoSeKI0FvS82yN0SfU5MLppM08yhy3jsk4aEyrPOjdJojGsnim vTlaZqNbEYA5g== To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Alice Ryhl From: y86-dev@protonmail.com Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev Subject: [PATCH v3 12/13] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` Message-ID: <20230329223239.138757-13-y86-dev@protonmail.com> Feedback-ID: 40624463:user:proton Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable From: Benno Lossin `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 --- rust/kernel/lib.rs | 1 - rust/kernel/sync/arc.rs | 14 ++++++++++++-- 2 files changed, 12 insertions(+), 3 deletions(-) diff --git a/rust/kernel/lib.rs b/rust/kernel/lib.rs index 3e2777d26ff5..d9df77132fa2 100644 --- a/rust/kernel/lib.rs +++ b/rust/kernel/lib.rs @@ -27,7 +27,6 @@ #[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 (thi= s crate). extern crate self as kernel; diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 77a3833cc265..4ed6329a5e5f 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -18,6 +18,7 @@ use crate::{ bindings, error::{Error, Result}, + init, init::{InPlaceInit, Init, PinInit}, types::{ForeignOwnable, Opaque}, }; @@ -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 { _p: PhantomData>, } +#[pin_data] #[repr(C)] struct ArcInner { refcount: Opaque, @@ -501,9 +504,16 @@ impl UniqueArc { /// Tries to allocate a new [`UniqueArc`] instance whose contents are = not initialised yet. pub fn try_new_uninit() -> Result>> { - Ok(UniqueArc::> { + // INVARIANT: The refcount is initialised to a non-zero value. + let inner =3D Box::init(init!(ArcInner { + // SAFETY: There are no safety requirements for this FFI call. + refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }), + data <- init::uninit(), + }))?; + 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