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[2620:137:e000::1:20]) by mx.google.com with ESMTP id e27-20020a170906081b00b00931563028c0si4903808ejd.282.2023.04.08.00.55.21; Sat, 08 Apr 2023 00:55:44 -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=@gmail.com header.s=20210112 header.b=mQD2FNQM; 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=NONE sp=QUARANTINE dis=NONE) header.from=gmail.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229988AbjDHHyH (ORCPT + 99 others); Sat, 8 Apr 2023 03:54:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58924 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229785AbjDHHyA (ORCPT ); Sat, 8 Apr 2023 03:54:00 -0400 Received: from mail-oa1-x34.google.com (mail-oa1-x34.google.com [IPv6:2001:4860:4864:20::34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F0232903E; Sat, 8 Apr 2023 00:53:58 -0700 (PDT) Received: by mail-oa1-x34.google.com with SMTP id 586e51a60fabf-1842cddca49so877298fac.1; Sat, 08 Apr 2023 00:53:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680940437; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=Ty2c9HDR/6nIOmkOFdir3f2Vau2dO37PR6ULzCuywyo=; b=mQD2FNQM14xtdowH9iz3u9KrxtWYxuVEiLHuuONTmMgyyrzvr0SECC32EA1W0hXf0A Q0aJQ9U0KyozWxckkzcvoIfVqnlAmirDs9ML1dihRP7QD44WRk7u/GaBF1R4GWaf31X3 rIpq3hGKjCh6YP6XhWpao8Or9mRlwtpbKTs2Q/t3Y8DNPYD49G4EDQQZ75U6ZRghYuCD kHchuY27fpbv4NVn47Zu98ou0tcbDmJqxmgJBLEfFoHzGNa1Fst2IBwoqcwOYgYJ7yvH zMHeEUNyQ2i8XLWjtesvoy5BIH6M6Y8/NXoFWdaI9wbEWkT7QWy8Ok01C1e7eulWLVkD v9NQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680940437; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=Ty2c9HDR/6nIOmkOFdir3f2Vau2dO37PR6ULzCuywyo=; b=uh8L0dolSCRkMGK/NImylADgNkcLg+JBnLGAiZ8Efj2vkN8imi/754vH64rWOMljNM a901NVkcwqI4eVTnnNi5qNbWgf6OrtACT1TVZ6i9H47HQrpdVng/AhAJVI3m8zQVhraD qmis00EMN0fGyB1R5RG+96WBf6Ct40cGwakKPAAaYcHYm57ZX+nJEM1743vjgEszWtHF Tnw4WHoXQSQ2iarLthObqpB2pKyjZaQLNPGvn6XbWJ9KcL9P2h6e7L5afsVKla5i/E/L hKI3BQQCXyR2IexWj7ZQmTT/C88ZtGkcu+129sPLbHIVWg5lmPJ045q1wqN9JyuEnXKn PfyQ== X-Gm-Message-State: AAQBX9cA17/SfMzLZPnBx/tEuhC1ajs8r1gBh7U2Gaq6XdIEhVMS/E1g Fe13FvU4CW6dYhSPBh4WhpxXSNyo1xY= X-Received: by 2002:a05:6870:a793:b0:184:286b:8abc with SMTP id x19-20020a056870a79300b00184286b8abcmr850876oao.11.1680940437175; Sat, 08 Apr 2023 00:53:57 -0700 (PDT) Received: from wedsonaf-dev.home.lan ([189.124.190.154]) by smtp.googlemail.com with ESMTPSA id o6-20020a4a9586000000b0051ffe0fe11bsm2435175ooi.6.2023.04.08.00.53.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Apr 2023 00:53:56 -0700 (PDT) From: Wedson Almeida Filho To: rust-for-linux@vger.kernel.org Cc: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?q?B?= =?utf-8?q?j=C3=B6rn_Roy_Baron?= , linux-kernel@vger.kernel.org, Wedson Almeida Filho Subject: [PATCH v3 02/13] rust: sync: introduce `Lock` and `Guard` Date: Sat, 8 Apr 2023 04:53:29 -0300 Message-Id: <20230408075340.25237-2-wedsonaf@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20230408075340.25237-1-wedsonaf@gmail.com> References: <20230408075340.25237-1-wedsonaf@gmail.com> MIME-Version: 1.0 X-Spam-Status: No, score=-0.2 required=5.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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?1762593912934870664?= X-GMAIL-MSGID: =?utf-8?q?1762593912934870664?= From: Wedson Almeida Filho They are generic Rust implementations of a lock and a lock guard that contain code that is common to all locks. Different backends will be introduced in subsequent commits. Suggested-by: Gary Guo Signed-off-by: Wedson Almeida Filho Reviewed-by: Martin Rodriguez Reboredo --- v1 -> v2: No changes v2 -> v3: Use new Opaque::ffi_init from Benno's series rust/kernel/sync.rs | 2 +- rust/kernel/sync/lock.rs | 162 +++++++++++++++++++++++++++++++++++++++ 2 files changed, 163 insertions(+), 1 deletion(-) create mode 100644 rust/kernel/sync/lock.rs diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs index 541d235ffbeb..81b0998eaa18 100644 --- a/rust/kernel/sync.rs +++ b/rust/kernel/sync.rs @@ -8,6 +8,7 @@ use crate::types::Opaque; mod arc; +pub mod lock; pub use arc::{Arc, ArcBorrow, UniqueArc}; @@ -25,7 +26,6 @@ impl LockClassKey { Self(Opaque::uninit()) } - #[allow(dead_code)] pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key { self.0.get() } diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs new file mode 100644 index 000000000000..3fa4eefde740 --- /dev/null +++ b/rust/kernel/sync/lock.rs @@ -0,0 +1,162 @@ +// SPDX-License-Identifier: GPL-2.0 + +//! Generic kernel lock and guard. +//! +//! It contains a generic Rust lock and guard that allow for different backends (e.g., mutexes, +//! spinlocks, raw spinlocks) to be provided with minimal effort. + +use super::LockClassKey; +use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque}; +use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned}; +use macros::pin_data; + +/// The "backend" of a lock. +/// +/// It is the actual implementation of the lock, without the need to repeat patterns used in all +/// locks. +/// +/// # Safety +/// +/// - Implementers must ensure that only one thread/CPU may access the protected data once the lock +/// is owned, that is, between calls to `lock` and `unlock`. +pub unsafe trait Backend { + /// The state required by the lock. + type State; + + /// The state required to be kept between lock and unlock. + type GuardState; + + /// Initialises the lock. + /// + /// # Safety + /// + /// `ptr` must be valid for write for the duration of the call, while `name` and `key` must + /// remain valid for read indefinitely. + unsafe fn init( + ptr: *mut Self::State, + name: *const core::ffi::c_char, + key: *mut bindings::lock_class_key, + ); + + /// Acquires the lock, making the caller its owner. + /// + /// # Safety + /// + /// Callers must ensure that [`Backend::init`] has been previously called. + #[must_use] + unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState; + + /// Releases the lock, giving up its ownership. + /// + /// # Safety + /// + /// It must only be called by the current owner of the lock. + unsafe fn unlock(ptr: *mut Self::State, guard_state: &Self::GuardState); +} + +/// A mutual exclusion primitive. +/// +/// Exposes one of the kernel locking primitives. Which one is exposed depends on the lock banckend +/// specified as the generic parameter `T`. +#[pin_data] +pub struct Lock { + /// The kernel lock object. + #[pin] + state: Opaque, + + /// Some locks are known to be self-referential (e.g., mutexes), while others are architecture + /// or config defined (e.g., spinlocks). So we conservatively require them to be pinned in case + /// some architecture uses self-references now or in the future. + #[pin] + _pin: PhantomPinned, + + /// The data protected by the lock. + data: UnsafeCell, +} + +// SAFETY: `Lock` can be transferred across thread boundaries iff the data it protects can. +unsafe impl Send for Lock {} + +// SAFETY: `Lock` serialises the interior mutability it provides, so it is `Sync` as long as the +// data it protects is `Send`. +unsafe impl Sync for Lock {} + +impl Lock { + /// Constructs a new lock initialiser. + #[allow(clippy::new_ret_no_self)] + pub fn new(t: T, name: &'static CStr, key: &'static LockClassKey) -> impl PinInit { + pin_init!(Self { + data: UnsafeCell::new(t), + _pin: PhantomPinned, + // SAFETY: `slot` is valid while the closure is called and both `name` and `key` have + // static lifetimes so they live indefinitely. + state <- Opaque::ffi_init(|slot| unsafe { + B::init(slot, name.as_char_ptr(), key.as_ptr()) + }), + }) + } +} + +impl Lock { + /// Acquires the lock and gives the caller access to the data protected by it. + pub fn lock(&self) -> Guard<'_, T, B> { + // SAFETY: The constructor of the type calls `init`, so the existence of the object proves + // that `init` was called. + let state = unsafe { B::lock(self.state.get()) }; + // SAFETY: The lock was just acquired. + unsafe { Guard::new(self, state) } + } +} + +/// A lock guard. +/// +/// Allows mutual exclusion primitives that implement the `Backend` trait to automatically unlock +/// when a guard goes out of scope. It also provides a safe and convenient way to access the data +/// protected by the lock. +#[must_use = "the lock unlocks immediately when the guard is unused"] +pub struct Guard<'a, T: ?Sized, B: Backend> { + pub(crate) lock: &'a Lock, + pub(crate) state: B::GuardState, + _not_send: PhantomData<*mut ()>, +} + +// SAFETY: `Guard` is sync when the data protected by the lock is also sync. +unsafe impl Sync for Guard<'_, T, B> {} + +impl core::ops::Deref for Guard<'_, T, B> { + type Target = T; + + fn deref(&self) -> &Self::Target { + // SAFETY: The caller owns the lock, so it is safe to deref the protected data. + unsafe { &*self.lock.data.get() } + } +} + +impl core::ops::DerefMut for Guard<'_, T, B> { + fn deref_mut(&mut self) -> &mut Self::Target { + // SAFETY: The caller owns the lock, so it is safe to deref the protected data. + unsafe { &mut *self.lock.data.get() } + } +} + +impl Drop for Guard<'_, T, B> { + fn drop(&mut self) { + // SAFETY: The caller owns the lock, so it is safe to unlock it. + unsafe { B::unlock(self.lock.state.get(), &self.state) }; + } +} + +impl<'a, T: ?Sized, B: Backend> Guard<'a, T, B> { + /// Constructs a new immutable lock guard. + /// + /// # Safety + /// + /// The caller must ensure that it owns the lock. + pub(crate) unsafe fn new(lock: &'a Lock, state: B::GuardState) -> Self { + Self { + lock, + state, + _not_send: PhantomData, + } + } +}