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[2620:137:e000::1:20]) by mx.google.com with ESMTP id n20-20020a634d54000000b005020ed55feasi5320336pgl.633.2023.03.12.18.26.41; Sun, 12 Mar 2023 18:26:55 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@protonmail.com header.s=protonmail3 header.b=bgkauahI; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=protonmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229891AbjCMBY5 (ORCPT + 99 others); Sun, 12 Mar 2023 21:24:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59306 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229898AbjCMBYw (ORCPT ); Sun, 12 Mar 2023 21:24:52 -0400 Received: from mail-0301.mail-europe.com (mail-0301.mail-europe.com [188.165.51.139]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BC1EA3755F for ; Sun, 12 Mar 2023 18:24:39 -0700 (PDT) Date: Mon, 13 Mar 2023 01:24:27 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=protonmail3; t=1678670676; x=1678929876; bh=cuPbajrG04DWKCw3k4p3kDYIB2rguZndGg7ZIQkRsVg=; h=Date:To:From:Cc:Subject:Message-ID:Feedback-ID:From:To:Cc:Date: Subject:Reply-To:Feedback-ID:Message-ID:BIMI-Selector; b=bgkauahIibdtHbqnw5u75ZP+3pa8tnBflxvHg0QDi+LaQ4hS5neh7oZPKGxxF8YMX uiFMBdnsvkybeMOngMrw5QQBU8O93YuyGNKnhIclhiE99yvkUPeB493/O2LHmIPdtC td7WAurrA1L9hA4RA7Ylv90LdtVgeHkIJIZ3ZujOGEcCAZBPwrJP/miBJ073UuMT0+ 5rZRh/N7nTEZAsX6c/bOncyEsIKOKeTGbruRtiHKGP6MyRTGZjsGx31iuV4Pj3EEYA 8QOqfgyNMFsyCSx7lRyv+P87iGZ1DO79SG3Kx5YYASMkqYWe3yjA7wJmbzIFycP7kI 7FT3k9SJgOjMA== To: "ojeda@kernel.org" , "alex.gaynor@gmail.com" , "wedsonaf@gmail.com" , "boqun.feng@gmail.com" , Gary Guo , "bjorn3_gh@protonmail.com" From: y86-dev Cc: "rust-for-linux@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "patches@lists.linux.dev" Subject: [PATCH v1 3/3] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` Message-ID: Feedback-ID: 40624463:user:proton MIME-Version: 1.0 X-Spam-Status: No, score=-2.8 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_LOW, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1760213929214227770?= X-GMAIL-MSGID: =?utf-8?q?1760213929214227770?= `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 | 12 +++++++++++- 2 files changed, 11 insertions(+), 2 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 (this crate). extern crate self as kernel; diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 5b4f64dd3ac8..6782d66039e1 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>> { + // INVARIANT: The refcount is initialised to a non-zero value. + let inner = 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()) }, }) } }