From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1391FC77B70 for ; Sat, 8 Apr 2023 07:55:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230173AbjDHHzV (ORCPT ); Sat, 8 Apr 2023 03:55:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32776 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230131AbjDHHzA (ORCPT ); Sat, 8 Apr 2023 03:55:00 -0400 Received: from mail-oi1-x22d.google.com (mail-oi1-x22d.google.com [IPv6:2607:f8b0:4864:20::22d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D916BFF0E; Sat, 8 Apr 2023 00:54:37 -0700 (PDT) Received: by mail-oi1-x22d.google.com with SMTP id w13so21006233oik.2; Sat, 08 Apr 2023 00:54:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; t=1680940463; 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=KRp/Oi/twJtl9aBTzuC+WObtxL9OqDuPbUJ1RtXTIfI=; b=R0+rGcdc6V1X+oez522zCJPvrVawIDxgxs86xe/wj1vfkFDC7N1DW0NXAtwgMp3+Vf RVoANubvriftXet27shk9KqP91cndUhCZpnsjDM/c33w5pemyGG8Tbwf+amF7KOlG7r0 AefeM63JNjreEDh/teGas2knHKSup6KUnX9XkRxwJTKMjvIuZkq0cp9XqvuwwpT6j6bd A1kKj7KumT8XVxZ9IyqX328eKB1PGCL9ct9317CwvwXveaCXgSP50MHirVijn4j0zDQB l4qFUmPcmViLJHRoLpZBfiIT8LXHRAk2KUzqNcgDtHIE72esLNq3zPxKfUd9h77cyFJX NPTQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680940463; 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=KRp/Oi/twJtl9aBTzuC+WObtxL9OqDuPbUJ1RtXTIfI=; b=wLG3wiogwoMTq9syr66w+S/yC+3lL7epmS9oNT3md2viZmv9/Ric4Zmwsqz6mLrORO HFN9cz2nftrfWdvBUysG0dZBr/hcxBAwpgoSm0nvMB7axR+UxcH5DtAOYn9V8B12eGXz AhMUQ2JVzqlZ6s1L3ynCIokBKG3JXr1l6goUHSbTURV5IdW/XK4OGL/PqxeMEAzO7Wmi JZEXGFEzNr6HFcb10zs9vRXKqK5HFNZcdN3ciFJ+6GtebCDA0TBPLrx/kAYrDCCKRr/J jwEq4nvycI32p91AMves0JUuwaIW6Z51ab+NRJFDkcehsCiExIQ1kRAkHT6DcB9+WWgi rEgQ== X-Gm-Message-State: AAQBX9fzhgaMQRv5KFmkU4WDBtqqSsayu9UJcK8+eGNhs2fZ5mdgjNX9 BwrYcG8eEvA/Tj9Q9mWzongyxIeThsw= X-Google-Smtp-Source: AKy350buTh+bhmz+hvu0w5SxbhLyyETFn1ixkdjrYZvxz2w1i0UCeDVJhgYrLQF2lRoJLzE0Rpxv3A== X-Received: by 2002:a54:4402:0:b0:387:87cd:11c6 with SMTP id k2-20020a544402000000b0038787cd11c6mr526748oiw.59.1680940463390; Sat, 08 Apr 2023 00:54:23 -0700 (PDT) Received: from wedsonaf-dev.home.lan ([189.124.190.154]) by smtp.googlemail.com with ESMTPSA id o6-20020a4a9586000000b0051ffe0fe11bsm2435175ooi.6.2023.04.08.00.54.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 08 Apr 2023 00:54:23 -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?Bj=C3=B6rn=20Roy=20Baron?= , linux-kernel@vger.kernel.org, Wedson Almeida Filho , Ingo Molnar , Peter Zijlstra Subject: [PATCH v3 10/13] rust: introduce `current` Date: Sat, 8 Apr 2023 04:53:37 -0300 Message-Id: <20230408075340.25237-10-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 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Wedson Almeida Filho This allows Rust code to get a reference to the current task without having to increment the refcount, but still guaranteeing memory safety. Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Wedson Almeida Filho --- v1 -> v2: Make `current` a macro to prevent it from escaping the caller v2 -> v3: - Mention `current` macro in `Task::current` - Hide implementation of `TaskRef` inside `Task::current` rust/helpers.c | 6 +++ rust/kernel/prelude.rs | 2 + rust/kernel/task.rs | 88 +++++++++++++++++++++++++++++++++++++++++- 3 files changed, 95 insertions(+), 1 deletion(-) diff --git a/rust/helpers.c b/rust/helpers.c index 58a194042c86..96441744030e 100644 --- a/rust/helpers.c +++ b/rust/helpers.c @@ -100,6 +100,12 @@ bool rust_helper_refcount_dec_and_test(refcount_t *r) } EXPORT_SYMBOL_GPL(rust_helper_refcount_dec_and_test); +struct task_struct *rust_helper_get_current(void) +{ + return current; +} +EXPORT_SYMBOL_GPL(rust_helper_get_current); + void rust_helper_get_task_struct(struct task_struct *t) { get_task_struct(t); diff --git a/rust/kernel/prelude.rs b/rust/kernel/prelude.rs index fcdc511d2ce8..c28587d68ebc 100644 --- a/rust/kernel/prelude.rs +++ b/rust/kernel/prelude.rs @@ -36,3 +36,5 @@ pub use super::error::{code::*, Error, Result}; pub use super::{str::CStr, ThisModule}; pub use super::init::{InPlaceInit, Init, PinInit}; + +pub use super::current; diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index d70cad131956..5269a562cb1b 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -5,7 +5,17 @@ //! C header: [`include/linux/sched.h`](../../../../include/linux/sched.h). use crate::{bindings, types::Opaque}; -use core::ptr; +use core::{marker::PhantomData, ops::Deref, ptr}; + +/// Returns the currently running task. +#[macro_export] +macro_rules! current { + () => { + // SAFETY: Deref + addr-of below create a temporary `TaskRef` that cannot outlive the + // caller. + unsafe { &*$crate::task::Task::current() } + }; +} /// Wraps the kernel's `struct task_struct`. /// @@ -15,6 +25,42 @@ use core::ptr; /// /// Instances of this type are always ref-counted, that is, a call to `get_task_struct` ensures /// that the allocation remains valid at least until the matching call to `put_task_struct`. +/// +/// # Examples +/// +/// The following is an example of getting the PID of the current thread with zero additional cost +/// when compared to the C version: +/// +/// ``` +/// let pid = current!().pid(); +/// ``` +/// +/// Getting the PID of the current process, also zero additional cost: +/// +/// ``` +/// let pid = current!().group_leader().pid(); +/// ``` +/// +/// Getting the current task and storing it in some struct. The reference count is automatically +/// incremented when creating `State` and decremented when it is dropped: +/// +/// ``` +/// use kernel::{task::Task, types::ARef}; +/// +/// struct State { +/// creator: ARef, +/// index: u32, +/// } +/// +/// impl State { +/// fn new() -> Self { +/// Self { +/// creator: current!().into(), +/// index: 0, +/// } +/// } +/// } +/// ``` #[repr(transparent)] pub struct Task(pub(crate) Opaque); @@ -27,6 +73,46 @@ unsafe impl Sync for Task {} type Pid = bindings::pid_t; impl Task { + /// Returns a task reference for the currently executing task/thread. + /// + /// The recommended way to get the current task/thread is to use the + /// [`current`](crate::current) macro because it is safe. + /// + /// # Safety + /// + /// Callers must ensure that the returned object doesn't outlive the current task/thread. + pub unsafe fn current() -> impl Deref { + pub struct TaskRef<'a> { + task: &'a Task, + _not_send: PhantomData<*mut ()>, + } + + impl Deref for TaskRef<'_> { + type Target = Task; + + fn deref(&self) -> &Self::Target { + self.task + } + } + + impl From> for crate::types::ARef { + fn from(t: TaskRef<'_>) -> Self { + t.deref().into() + } + } + + // SAFETY: Just an FFI call with no additional safety requirements. + let ptr = unsafe { bindings::get_current() }; + + TaskRef { + // SAFETY: If the current thread is still running, the current task is valid. Given + // that `TaskRef` is not `Send`, we know it cannot be transferred to another thread + // (where it could potentially outlive the caller). + task: unsafe { &*ptr.cast() }, + _not_send: PhantomData, + } + } + /// Returns the group leader of the given task. pub fn group_leader(&self) -> &Task { // SAFETY: By the type invariant, we know that `self.0` is a valid task. Valid tasks always -- 2.34.1