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Fri, 02 Feb 2024 02:55:49 -0800 (PST) Date: Fri, 2 Feb 2024 10:55:35 +0000 In-Reply-To: <20240202-alice-file-v4-0-fc9c2080663b@google.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240202-alice-file-v4-0-fc9c2080663b@google.com> X-Developer-Key: i=aliceryhl@google.com; a=openpgp; fpr=49F6C1FAA74960F43A5B86A1EE7A392FDE96209F X-Developer-Signature: v=1; a=openpgp-sha256; l=5180; i=aliceryhl@google.com; h=from:subject:message-id; bh=7gwoE0vtO/2/iYZib8O58rbMHk3Wy9KYeSDPJyHPimY=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBlvMjJVrh8psmguMzY4qssJLn8fU7x6TwLXZl0A b26AWdaCAmJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZbzIyQAKCRAEWL7uWMY5 RsolD/90eoXCySNpVOb7NYRwSd+K9mdkE0Zgp+frXI3IfySfd1n78V+DlKjLpoHuW9yKpDOFThM FVZmlkIbki2JVo9lQRrVkXk2SB/jYE1wiIu7wbMN2T4ptQArp7/tLdI158J+m/Y475QCmy6yb1o pgxmY0UWqcmFmMv7bjHCtHqGC3zlfR6PND0fuZISbwIXKxEzgrWsw8OgIzoPFhUj1CaYQnTFV3P oAKBBFrQ+0o8IooTJ1B34MkVcx706eNu76S4KxBlPTzD9SxdLrKyz4opCYHL/p80T2SPpIjP188 08Ha/Cxy8O2pYBiHRQG0Qdg7bnjma8ZaCcclvUg4e1WqVgcYEoaz4xaDDmchAfYao92E/4lGQVl SB969da/RLsuz3NjQTa4xkHwHi52i4AqGYxjn53r/kaiOCuQZaCWohdVTmSUYvbxh1LGwp2C7fv 5lTGSpE6ej8oALanvEfgMz45GsYtTcASuQIogQFmAv1ai6bbOCSYo4zYtfnshTvAn39bLB7FY9i iSIfPamxyb94sXgTK14n6r1M0t+j5wQoSuvlmeeECJ/7aiDoZc11FhYISfw7ZQfHs29Am9qknLV RdfX+lzQLuncgDEMDEEnHrCDSbQteIDfXKU2jW5nk5Vs7KOfc7HwlnKDsnrJvXfreFCM1Fbq3VW Y//l4Ceyv/iuXNg== X-Mailer: git-send-email 2.43.0.594.gd9cf4e227d-goog Message-ID: <20240202-alice-file-v4-1-fc9c2080663b@google.com> Subject: [PATCH v4 1/9] rust: types: add `NotThreadSafe` From: Alice Ryhl To: Miguel Ojeda , Alex Gaynor , Wedson Almeida Filho , Boqun Feng , Gary Guo , " =?utf-8?q?Bj=C3=B6rn_Roy_Baron?= " , Benno Lossin , Andreas Hindborg , Peter Zijlstra , Alexander Viro , Christian Brauner , Greg Kroah-Hartman , " =?utf-8?q?Arve_Hj?= =?utf-8?q?=C3=B8nnev=C3=A5g?= " , Todd Kjos , Martijn Coenen , Joel Fernandes , Carlos Llamas , Suren Baghdasaryan , Dan Williams , Kees Cook , Matthew Wilcox , Thomas Gleixner Cc: Daniel Xu , Alice Ryhl , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org This introduces a new marker type for types that shouldn't be thread safe. By adding a field of this type to a struct, it becomes non-Send and non-Sync, which means that it cannot be accessed in any way from threads other than the one it was created on. This is useful for APIs that require globals such as `current` to remain constant while the value exists. We update two existing users in the Kernel to use this helper: * `Task::current()` - moving the return type of this value to a different thread would not be safe as you can no longer be guaranteed that the `current` pointer remains valid. * Lock guards. Mutexes and spinlocks should be unlocked on the same thread as where they were locked, so we enforce this using the Send trait. There are also additional users in later patches of this patchset. See [1] and [2] for the discussion that led to the introducion of this patch. Link: https://lore.kernel.org/all/nFDPJFnzE9Q5cqY7FwSMByRH2OAn_BpI4H53NQfWIlN6I2qfmAqnkp2wRqn0XjMO65OyZY4h6P4K2nAGKJpAOSzksYXaiAK_FoH_8QbgBI4=@proton.me/ [1] Link: https://lore.kernel.org/all/nFDPJFnzE9Q5cqY7FwSMByRH2OAn_BpI4H53NQfWIlN6I2qfmAqnkp2wRqn0XjMO65OyZY4h6P4K2nAGKJpAOSzksYXaiAK_FoH_8QbgBI4=@proton.me/ [2] Suggested-by: Benno Lossin Reviewed-by: Benno Lossin Signed-off-by: Alice Ryhl Reviewed-by: Trevor Gross Reviewed-by: Martin Rodriguez Reboredo --- rust/kernel/sync/lock.rs | 15 +++++++++++---- rust/kernel/task.rs | 10 ++++++---- rust/kernel/types.rs | 17 +++++++++++++++++ 3 files changed, 34 insertions(+), 8 deletions(-) diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs index 149a5259d431..d08d9d32915a 100644 --- a/rust/kernel/sync/lock.rs +++ b/rust/kernel/sync/lock.rs @@ -6,8 +6,15 @@ //! spinlocks, raw spinlocks) to be provided with minimal effort. use super::LockClassKey; -use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard}; -use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned}; +use crate::{ + bindings, + init::PinInit, + pin_init, + str::CStr, + types::ScopeGuard, + types::{NotThreadSafe, Opaque}, +}; +use core::{cell::UnsafeCell, marker::PhantomPinned}; use macros::pin_data; pub mod mutex; @@ -132,7 +139,7 @@ pub fn lock(&self) -> Guard<'_, T, B> { pub struct Guard<'a, T: ?Sized, B: Backend> { pub(crate) lock: &'a Lock, pub(crate) state: B::GuardState, - _not_send: PhantomData<*mut ()>, + _not_send: NotThreadSafe, } // SAFETY: `Guard` is sync when the data protected by the lock is also sync. @@ -184,7 +191,7 @@ pub(crate) unsafe fn new(lock: &'a Lock, state: B::GuardState) -> Self { Self { lock, state, - _not_send: PhantomData, + _not_send: NotThreadSafe, } } } diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index a3a4007db682..148a4f4eb7a8 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -4,10 +4,12 @@ //! //! C header: [`include/linux/sched.h`](srctree/include/linux/sched.h). -use crate::{bindings, types::Opaque}; +use crate::{ + bindings, + types::{NotThreadSafe, Opaque}, +}; use core::{ ffi::{c_int, c_long, c_uint}, - marker::PhantomData, ops::Deref, ptr, }; @@ -106,7 +108,7 @@ impl Task { pub unsafe fn current() -> impl Deref { struct TaskRef<'a> { task: &'a Task, - _not_send: PhantomData<*mut ()>, + _not_send: NotThreadSafe, } impl Deref for TaskRef<'_> { @@ -125,7 +127,7 @@ fn deref(&self) -> &Self::Target { // 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, + _not_send: NotThreadSafe, } } diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index fdb778e65d79..5841f7512971 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -387,3 +387,20 @@ pub enum Either { /// Constructs an instance of [`Either`] containing a value of type `R`. Right(R), } + +/// Zero-sized type to mark types not [`Send`]. +/// +/// Add this type as a field to your struct if your type should not be sent to a different task. +/// Since [`Send`] is an auto trait, adding a single field that is `!Send` will ensure that the +/// whole type is `!Send`. +/// +/// If a type is `!Send` it is impossible to give control over an instance of the type to another +/// task. This is useful when a type stores task-local information for example file descriptors. +pub type NotThreadSafe = PhantomData<*mut ()>; + +/// Used to construct instances of type [`NotThreadSafe`] similar to how we construct +/// `PhantomData`. +/// +/// [`NotThreadSafe`]: type@NotThreadSafe +#[allow(non_upper_case_globals)] +pub const NotThreadSafe: NotThreadSafe = PhantomData;