From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-10630.protonmail.ch (mail-10630.protonmail.ch [79.135.106.30]) (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 311402561D6 for ; Tue, 25 Mar 2025 11:57:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=79.135.106.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903833; cv=none; b=t+yWCUvQ0QJmH/KDIYSvuhAQuZ9zIRFJdVc/srpg5JYyLoe0FhJ38vIOHLAGCzmznwGmpEZeidGOH4y9nRXLQwgSFA3+OBhLFP0FttzSHP3admDnbFNyTnFZosk/pZGP01xzPAPMpYR/8O4edCVqB0JlsPuQv3nR19c27t/clwA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742903833; c=relaxed/simple; bh=C0RwrWGOGxfVYV0ZG6ke5fAapyZFN2+Z6PniXzJrneM=; h=Date:To:From:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ca6ebax5I8s5uyEXLt0phEs2UfvwgKlr4WqnVI0CeET3SYSm4aaOcR4rriewbnLDlvpC5tsXL1oV6I9j+rzi+KUpwKlWj7pOdmQJTiz963WyYhpilgY4yl9x0byNobsKLzy/ckfSxUDION3spbmlQFiXe7HXUpf640rTiuLwbqw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me; spf=pass smtp.mailfrom=pm.me; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b=OQ1u5HEM; arc=none smtp.client-ip=79.135.106.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=pm.me Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=pm.me Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=pm.me header.i=@pm.me header.b="OQ1u5HEM" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=pm.me; s=protonmail3; t=1742903828; x=1743163028; bh=plqB4STdtbnS+5Ca9rypCcPrWoObRt1eRhm7vBhyeac=; 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:List-Unsubscribe:List-Unsubscribe-Post; b=OQ1u5HEMCzPLzsdQ1wInuZl0L76UFr3nDWBfQqLaGuFke6zyeAK8IMenOEFrPFv4P U1CiFmgtZW2T5YyRmUcxZUc82bam7fAzGrx9qvfRGjQ7ZUQSS94qLOqUi75iAufmjN LV3mzctjH53G/9nO+HqeFjyJrEzBH4Oymu65RdfPvwo9cTB1djdMqoq0+qm2PowT+2 MXSCimEeMJl0nowsupXXKfhGlUSr+mjSpTefFbLIQa5zpUXjkkI/9nSXjkpfJubOtI QDJRkuepWgp/gcti6dNex8FKOPzw8P+SzEOrFmRK5Xuz1mwx7UsufRXNDAsB5Gu4OQ ALnUEOmwaQ+gQ== Date: Tue, 25 Mar 2025 11:57:01 +0000 To: Miguel Ojeda , Alex Gaynor , Boqun Feng , Gary Guo , =?utf-8?Q?Bj=C3=B6rn_Roy_Baron?= , Benno Lossin , Andreas Hindborg , Alice Ryhl , Trevor Gross , Asahi Lina From: Oliver Mangold Cc: rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org, Oliver Mangold Subject: [PATCH v9 2/5] rust: Rename AlwaysRefCounted to RefCounted Message-ID: <20250325-unique-ref-v9-2-e91618c1de26@pm.me> In-Reply-To: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> References: <20250325-unique-ref-v9-0-e91618c1de26@pm.me> Feedback-ID: 31808448:user:proton X-Pm-Message-ID: 52e1f0a16bef519039adc580640563f32e61c020 Precedence: bulk X-Mailing-List: rust-for-linux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable AlwaysRefCounted will become a marker trait to indicate that it is allowed to obtain an ARef from a `&`, which cannot be allowed for types which are also Ownable. Signed-off-by: Oliver Mangold Suggested-by: Alice Ryhl --- rust/kernel/block/mq/request.rs | 10 +++++++--- rust/kernel/cred.rs | 8 ++++++-- rust/kernel/device.rs | 8 ++++++-- rust/kernel/fs/file.rs | 10 +++++++--- rust/kernel/pid_namespace.rs | 8 ++++++-- rust/kernel/task.rs | 6 +++++- rust/kernel/types.rs | 41 ++++++++++++++++++++++++-------------= ---- 7 files changed, 61 insertions(+), 30 deletions(-) diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request= .rs index 7943f43b957532749f5a95eee5546bf4f2b6cc5a..f47a13de1e073d564ae224d2e0d= 5cfb875f04da6 100644 --- a/rust/kernel/block/mq/request.rs +++ b/rust/kernel/block/mq/request.rs @@ -8,7 +8,7 @@ bindings, block::mq::Operations, error::Result, - types::{ARef, AlwaysRefCounted, Opaque}, + types::{ARef, AlwaysRefCounted, Opaque, RefCounted}, }; use core::{ marker::PhantomData, @@ -227,10 +227,10 @@ fn atomic_relaxed_op_unless(target: &AtomicU64, op: i= mpl Fn(u64) -> u64, pred: u } =20 // SAFETY: All instances of `Request` are reference counted. This -// implementation of `AlwaysRefCounted` ensure that increments to the ref = count +// implementation of `RefCounted` ensure that increments to the ref count // keeps the object alive in memory at least until a matching reference co= unt // decrement is executed. -unsafe impl AlwaysRefCounted for Request { +unsafe impl RefCounted for Request { fn inc_ref(&self) { let refcount =3D &self.wrapper_ref().refcount(); =20 @@ -260,3 +260,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull) { } } } + +// SAFETY: We currently do not implement `Ownable`, thus it is okay to can= obtain an `ARef` +// from a `&Request` (but this will change in the future). +unsafe impl AlwaysRefCounted for Request {} diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs index 81d67789b16f243e7832ff3b2e5e479a1ab2bf9e..e04d1021130eb1ec46fe48feb08= 8959da7656d66 100644 --- a/rust/kernel/cred.rs +++ b/rust/kernel/cred.rs @@ -11,7 +11,7 @@ use crate::{ bindings, task::Kuid, - types::{AlwaysRefCounted, Opaque}, + types::{AlwaysRefCounted, Opaque, RefCounted}, }; =20 /// Wraps the kernel's `struct cred`. @@ -71,7 +71,7 @@ pub fn euid(&self) -> Kuid { } =20 // SAFETY: The type invariants guarantee that `Credential` is always ref-c= ounted. -unsafe impl AlwaysRefCounted for Credential { +unsafe impl RefCounted for Credential { fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. unsafe { bindings::get_cred(self.0.get()) }; @@ -83,3 +83,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull) { unsafe { bindings::put_cred(obj.cast().as_ptr()) }; } } + +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +// `&Credential`. +unsafe impl AlwaysRefCounted for Credential {} diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs index db2d9658ba47d9c492bc813ce3eb2ff29703ca31..189298518dc184405b1d62404b1= 90d4c0b08b7ad 100644 --- a/rust/kernel/device.rs +++ b/rust/kernel/device.rs @@ -7,7 +7,7 @@ use crate::{ bindings, str::CStr, - types::{ARef, Opaque}, + types::{ARef, AlwaysRefCounted, Opaque, RefCounted}, }; use core::{fmt, ptr}; =20 @@ -190,7 +190,7 @@ pub fn property_present(&self, name: &CStr) -> bool { } =20 // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::types::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the= refcount is non-zero. unsafe { bindings::get_device(self.as_raw()) }; @@ -202,6 +202,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `Device` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + // SAFETY: As by the type invariant `Device` can be sent to any thread. unsafe impl Send for Device {} =20 diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs index e03dbe14d62a566349c4100f2f78b17d4c79aab5..a7836cc754e7927b6addc3bd06c= fe8c8119f1d9f 100644 --- a/rust/kernel/fs/file.rs +++ b/rust/kernel/fs/file.rs @@ -11,7 +11,7 @@ bindings, cred::Credential, error::{code::*, Error, Result}, - types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque}, + types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque, RefCounted}, }; use core::ptr; =20 @@ -190,7 +190,7 @@ unsafe impl Sync for File {} =20 // SAFETY: The type invariants guarantee that `File` is always ref-counted= . This implementation // makes `ARef` own a normal refcount. -unsafe impl AlwaysRefCounted for File { +unsafe impl RefCounted for File { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. @@ -205,6 +205,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +/// `&File`. +unsafe impl AlwaysRefCounted for File {} + /// Wraps the kernel's `struct file`. Not thread safe. /// /// This type represents a file that is not known to be safe to transfer a= cross thread boundaries. @@ -225,7 +229,7 @@ pub struct LocalFile { =20 // SAFETY: The type invariants guarantee that `LocalFile` is always ref-co= unted. This implementation // makes `ARef` own a normal refcount. -unsafe impl AlwaysRefCounted for LocalFile { +unsafe impl RefCounted for LocalFile { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs index 0e93808e4639b37dd77add5d79f64058dac7cb87..3e45e945b7509b9607266b2e0e6= ef130e7a1ed39 100644 --- a/rust/kernel/pid_namespace.rs +++ b/rust/kernel/pid_namespace.rs @@ -9,7 +9,7 @@ =20 use crate::{ bindings, - types::{AlwaysRefCounted, Opaque}, + types::{AlwaysRefCounted, RefCounted, Opaque}, }; use core::ptr; =20 @@ -44,7 +44,7 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_name= space) -> &'a Self { } =20 // SAFETY: Instances of `PidNamespace` are always reference-counted. -unsafe impl AlwaysRefCounted for PidNamespace { +unsafe impl RefCounted for PidNamespace { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. @@ -58,6 +58,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` +// from a `&PidNamespace`. +unsafe impl AlwaysRefCounted for PidNamespace {} + // SAFETY: // - `PidNamespace::dec_ref` can be called from any thread. // - It is okay to send ownership of `PidNamespace` across thread boundari= es. diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index 38da555a2bdbb71d698c671ad1a7a337e50c6600..5bdc0a348e6d549d66b002aa6b8= 92b61ce31214a 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -327,7 +327,7 @@ pub fn wake_up(&self) { } =20 // SAFETY: The type invariants guarantee that `Task` is always refcounted. -unsafe impl crate::types::AlwaysRefCounted for Task { +unsafe impl crate::types::RefCounted for Task { fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refc= ount is nonzero. unsafe { bindings::get_task_struct(self.as_ptr()) }; @@ -339,6 +339,10 @@ unsafe fn dec_ref(obj: ptr::NonNull) { } } =20 +// SAFETY: We do not implement `Ownable`, thus it is okay to can obtain an= `ARef` from a +// `&Task`. +unsafe impl crate::types::AlwaysRefCounted for Task {} + impl Kuid { /// Get the current euid. #[inline] diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 2cddbd3a2873b601419f7628c386431a63cb9692..c8b78bcad259132808cc38c56b9= f2bd525a0b755 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -388,11 +388,9 @@ pub const fn raw_get(this: *const Self) -> *mut T { } } =20 -/// Types that are _always_ reference counted. +/// Types that are internally reference counted. /// /// It allows such types to define their own custom ref increment and decr= ement functions. -/// Additionally, it allows users to convert from a shared reference `&T` = to an owned reference -/// [`ARef`]. /// /// This is usually implemented by wrappers to existing structures on the = C side of the code. For /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to c= reate reference-counted @@ -404,9 +402,8 @@ pub const fn raw_get(this: *const Self) -> *mut T { /// at least until matching decrements are performed. /// /// Implementers must also ensure that all instances are reference-counted= . (Otherwise they -/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_r= ef`] keep the object -/// alive.) -pub unsafe trait AlwaysRefCounted { +/// won't be able to honour the requirement that [`RefCounted::inc_ref`] k= eep the object alive.) +pub unsafe trait RefCounted { /// Increments the reference count on the object. fn inc_ref(&self); =20 @@ -419,11 +416,21 @@ pub unsafe trait AlwaysRefCounted { /// Callers must ensure that there was a previous matching increment t= o the reference count, /// and that the object is no longer used after its reference count is= decremented (as it may /// result in the object being freed), unless the caller owns another = increment on the refcount - /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls - /// [`AlwaysRefCounted::dec_ref`] once). + /// (e.g., it calls [`RefCounted::inc_ref`] twice, then calls [`RefCou= nted::dec_ref`] once). unsafe fn dec_ref(obj: NonNull); } =20 +/// An extension to RefCounted, which declares that it is allowed to conve= rt +/// from a shared reference `&T` to an owned reference [`ARef`]. +/// +/// # Safety +/// +/// Implementers must ensure that no safety invariants are violated by upg= rading an `&T` +/// to an [`ARef`]. In particular that implies [`AlwaysRefCounted`] and= [`Ownable`] +/// cannot be implemented for the same type, as this would allow to violat= e the uniqueness +/// guarantee of [`Owned`] by derefencing it into an `&T` and obtaining= an [`ARef`] from that. +pub unsafe trait AlwaysRefCounted: RefCounted {} + /// An owned reference to an always-reference-counted object. /// /// The object's reference count is automatically decremented when an inst= ance of [`ARef`] is @@ -434,7 +441,7 @@ pub unsafe trait AlwaysRefCounted { /// /// The pointer stored in `ptr` is non-null and valid for the lifetime of = the [`ARef`] instance. In /// particular, the [`ARef`] instance owns an increment on the underlying = object's reference count. -pub struct ARef { +pub struct ARef { ptr: NonNull, _p: PhantomData, } @@ -443,16 +450,16 @@ pub struct ARef { // it effectively means sharing `&T` (which is safe because `T` is `Sync`)= ; additionally, it needs // `T` to be `Send` because any thread that has an `ARef` may ultimatel= y access `T` using a // mutable reference, for example, when the reference count reaches zero a= nd `T` is dropped. -unsafe impl Send for ARef {} +unsafe impl Send for ARef {} =20 // SAFETY: It is safe to send `&ARef` to another thread when the underl= ying `T` is `Sync` // because it effectively means sharing `&T` (which is safe because `T` is= `Sync`); additionally, // it needs `T` to be `Send` because any thread that has a `&ARef` may = clone it and get an // `ARef` on that thread, so the thread may ultimately access `T` using= a mutable reference, for // example, when the reference count reaches zero and `T` is dropped. -unsafe impl Sync for ARef {} +unsafe impl Sync for ARef {} =20 -impl ARef { +impl ARef { /// Creates a new instance of [`ARef`]. /// /// It takes over an increment of the reference count on the underlyin= g object. @@ -481,12 +488,12 @@ pub unsafe fn from_raw(ptr: NonNull) -> Self { /// /// ``` /// use core::ptr::NonNull; - /// use kernel::types::{ARef, AlwaysRefCounted}; + /// use kernel::types::{ARef, RefCounted}; /// /// struct Empty {} /// /// # // SAFETY: TODO. - /// unsafe impl AlwaysRefCounted for Empty { + /// unsafe impl RefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull) {} /// } @@ -504,7 +511,7 @@ pub fn into_raw(me: Self) -> NonNull { } } =20 -impl Clone for ARef { +impl Clone for ARef { fn clone(&self) -> Self { self.inc_ref(); // SAFETY: We just incremented the refcount above. @@ -512,7 +519,7 @@ fn clone(&self) -> Self { } } =20 -impl Deref for ARef { +impl Deref for ARef { type Target =3D T; =20 fn deref(&self) -> &Self::Target { @@ -529,7 +536,7 @@ fn from(b: &T) -> Self { } } =20 -impl Drop for ARef { +impl Drop for ARef { fn drop(&mut self) { // SAFETY: The type invariants guarantee that the `ARef` owns the = reference we're about to // decrement. --=20 2.49.0