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[2620:137:e000::1:20]) by mx.google.com with ESMTP id bj11-20020a170902850b00b0019ad832a6f1si13850395plb.168.2023.03.21.12.55.26; Tue, 21 Mar 2023 12:55:39 -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=Og5rTLKV; 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 S229841AbjCUTut (ORCPT + 99 others); Tue, 21 Mar 2023 15:50:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49382 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229459AbjCUTur (ORCPT ); Tue, 21 Mar 2023 15:50:47 -0400 Received: from mail-4322.protonmail.ch (mail-4322.protonmail.ch [185.70.43.22]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3FDA04BE8E for ; Tue, 21 Mar 2023 12:50:24 -0700 (PDT) Date: Tue, 21 Mar 2023 19:50:10 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=protonmail3; t=1679428219; x=1679687419; bh=FNlCN3cHsJdz3JxxhBIbrUQMYy+/cKZuDeBnqnufKaQ=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: Feedback-ID:From:To:Cc:Date:Subject:Reply-To:Feedback-ID: Message-ID:BIMI-Selector; b=Og5rTLKVLPegceIya3psm7F/BerxmDfAFFqiPBwcw8oflNcadzZX9R6uU+QWVPW8O Y9m/o1sNRQzKtYQ6BXCErgut/8YWPXIndUd81bUaiMiklBCVvQ2PvNaOBjAlKDrAFQ RCu1WHJOJPIObRLRMaXKupJNP7Ia66UcCPfunnI3m4HAn5nR3oemQbU+oFkqewylpG Znv3UBP+tMUEanZndB8AqeG3RzPo2Am0W1cNvcKQTAAk2L/8v0vqid3Um/wWSfMI1z 3JoGgXoh/xEGgijXgNapaKTnIsq+P4ePMmTSN80lBVUADn/RYJ2V2k0Pb+5CtK1nlr Y2VRfX8RZylag== To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= From: Benno Lossin Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, patches@lists.linux.dev Subject: [PATCH v2 5/5] rust: sync: reduce stack usage of `UniqueArc::try_new_uninit` Message-ID: <20230321194934.908891-6-y86-dev@protonmail.com> In-Reply-To: <20230321194934.908891-1-y86-dev@protonmail.com> References: <20230321194934.908891-1-y86-dev@protonmail.com> Feedback-ID: 40624463:user:proton MIME-Version: 1.0 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_MSPIKE_H2, SPF_HELO_PASS,SPF_PASS,URIBL_BLOCKED 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?1761008460143491736?= X-GMAIL-MSGID: =?utf-8?q?1761008460143491736?= `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(-) -- 2.39.2 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..0518ff99b6c5 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()) }, }) } }