| Message ID | 20240202-alice-file-v4-1-fc9c2080663b@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | File abstractions needed by Rust Binder | expand |
On Fri, Feb 2, 2024 at 5:56 AM Alice Ryhl <aliceryhl@google.com> wrote: > > 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 s/introducion/introduction > 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 <benno.lossin@proton.me> > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > 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}, Formatting nit: ScopeGuard could probably be placed in the same group as NotThreadSafe & Opaque > [...] > + > +/// 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. I initially read this thinking it meant to include this type if your struct also had a FD rather than being part of the FD. Maybe This is useful to include in types that store or reference task-local information. A file descriptor is an example of one such type. > +pub type NotThreadSafe = PhantomData<*mut ()>; > + > +/// Used to construct instances of type [`NotThreadSafe`] similar to how we construct > +/// `PhantomData`. I think it sounds slightly better reworded from personal to passive, i.e. ... similar to how `PhantomData` is constructed. > +/// [`NotThreadSafe`]: type@NotThreadSafe > +#[allow(non_upper_case_globals)] > +pub const NotThreadSafe: NotThreadSafe = PhantomData; > -- > 2.43.0.594.gd9cf4e227d-goog This looks good, sounds nice to make the intent more clear. Nothing that isn't optional, so Reviewed-by: Trevor Gross <tmgross@umich.edu>
On 2/2/24 07:55, Alice Ryhl wrote: > 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 <benno.lossin@proton.me> > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > [...] Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
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<T, B>, 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<T, B>, 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<Target = Task> { 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<L, R> { /// 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;