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Fri, 09 Feb 2024 03:18:51 -0800 (PST) Date: Fri, 09 Feb 2024 11:18:14 +0000 In-Reply-To: <20240209-alice-file-v5-0-a37886783025@google.com> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240209-alice-file-v5-0-a37886783025@google.com> X-Developer-Key: i=aliceryhl@google.com; a=openpgp; fpr=49F6C1FAA74960F43A5B86A1EE7A392FDE96209F X-Developer-Signature: v=1; a=openpgp-sha256; l=5346; i=aliceryhl@google.com; h=from:subject:message-id; bh=Ot5zgSBuhhqw7Lyq5N1K+biVLFlimbZBNuPkWRRLiE4=; b=owEBbQKS/ZANAwAKAQRYvu5YxjlGAcsmYgBlxgoPyGfidEExgGJzTQr4EuqI+P+PF6rccTGHa xqqgMJnVTmJAjMEAAEKAB0WIQSDkqKUTWQHCvFIvbIEWL7uWMY5RgUCZcYKDwAKCRAEWL7uWMY5 RtXHD/96K2s5KP11BZAzeOUDVG85LrVgPCSeO7vAKxIsG5apeK3QUDwOM/nwagQGS2D4OsaDvSv jY2t+v1f2Jh8kUs/D1JuZs4o+nBB0B56BdMU1pWtEaBeXtPQB9xWHS87Ysi68C0iMUWsxIvI03i KlOXxSXBWQcX/9aPTzbTK18h+/DvTMmUxfDW6I6NhY8r0QxHsGZi8TlWjWUSfaii1kVzi9bC2hI MiOT8PNZAMBGvNsA/O94uIT57I2Dno5iLzD9xmQeiE58UEjQFE51OpKrPt9hEDRUl9biKklGa05 Gpf/Mgg1zgo3xu5+9ERTCQXXfV0qZn263lywYnnA8fhvMeh7WBVqo3TDq6yfYAEeAQwIqxn8Be1 +8MJj1ZScSdEkI73Ig+YUWiyuxZWcO7S10A850Y6I3vAPgMc5nVVPv0Do7zWYr9PxtG/7IcR3zo xcNqe4hV0glN6my3SOZFeopaHnPyGHHdy7PzeBbrvOIsURMUBoV4uswpsmE/yJdaCdSkzraWdjP X3eU6vFFhjE+KGoWfRwT9x4AH7cg2SLC4rHf8aRzqbgA9GeIY+SIJhLPBuCHQnyj6WSIPBCzl3U XOq4n47NHEf7vKsxh+1VoO6X6LP/L2mCtIn1aG6s3YVeMo16ff+2TkRKcO3ZiO4sU+80fwqlD5c eysAhO7o+dHjryQ== X-Mailer: b4 0.13-dev-26615 Message-ID: <20240209-alice-file-v5-1-a37886783025@google.com> Subject: [PATCH v5 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 Cc: Dan Williams , Kees Cook , Matthew Wilcox , Thomas Gleixner , Daniel Xu , linux-kernel@vger.kernel.org, rust-for-linux@vger.kernel.org, linux-fsdevel@vger.kernel.org, Alice Ryhl , Trevor Gross , Martin Rodriguez Reboredo 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 introduction 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 Reviewed-by: Trevor Gross Reviewed-by: Martin Rodriguez Reboredo Signed-off-by: Alice Ryhl --- rust/kernel/sync/lock.rs | 14 ++++++++++---- rust/kernel/task.rs | 10 ++++++---- rust/kernel/types.rs | 18 ++++++++++++++++++ 3 files changed, 34 insertions(+), 8 deletions(-) diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs index 149a5259d431..090b9ad63dc6 100644 --- a/rust/kernel/sync/lock.rs +++ b/rust/kernel/sync/lock.rs @@ -6,8 +6,14 @@ //! 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::{NotThreadSafe, ScopeGuard, Opaque}, +}; +use core::{cell::UnsafeCell, marker::PhantomPinned}; use macros::pin_data; pub mod mutex; @@ -132,7 +138,7 @@ 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 +190,7 @@ 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..ee1375d47df0 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -387,3 +387,21 @@ 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 to include in types that store or reference task-local information. A file +/// descriptor is an example of such task-local information. +pub type NotThreadSafe = PhantomData<*mut ()>; + +/// Used to construct instances of type [`NotThreadSafe`] similar to how `PhantomData` is +/// constructed. +/// +/// [`NotThreadSafe`]: type@NotThreadSafe +#[allow(non_upper_case_globals)] +pub const NotThreadSafe: NotThreadSafe = PhantomData;