On Thu, Jul 25, 2024 at 4:37 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Thu, Jul 25, 2024 at 02:27:34PM +0000, 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 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 <benno.lossin@xxxxxxxxx> > > Reviewed-by: Benno Lossin <benno.lossin@xxxxxxxxx> > > Reviewed-by: Trevor Gross <tmgross@xxxxxxxxx> > > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@xxxxxxxxx> > > Reviewed-by: Björn Roy Baron <bjorn3_gh@xxxxxxxxxxxxxx> > > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx> > > --- > > rust/kernel/sync/lock.rs | 13 +++++++++---- > > rust/kernel/task.rs | 10 ++++++---- > > rust/kernel/types.rs | 21 +++++++++++++++++++++ > > 3 files changed, 36 insertions(+), 8 deletions(-) > > > > diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs > > index f6c34ca4d819..d6e9bab114b8 100644 > > --- a/rust/kernel/sync/lock.rs > > +++ b/rust/kernel/sync/lock.rs > > @@ -6,8 +6,13 @@ > > //! spinlocks, raw spinlocks) to be provided with minimal effort. > > > > use super::LockClassKey; > > -use crate::{init::PinInit, pin_init, str::CStr, types::Opaque, types::ScopeGuard}; > > -use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned}; > > +use crate::{ > > + init::PinInit, > > + pin_init, > > + str::CStr, > > + types::{NotThreadSafe, Opaque, ScopeGuard}, > > +}; > > +use core::{cell::UnsafeCell, marker::PhantomPinned}; > > use macros::pin_data; > > > > pub mod mutex; > > @@ -139,7 +144,7 @@ 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. > > @@ -191,7 +196,7 @@ 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 55dff7e088bf..278c623de0c6 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::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, > > } > > } > > As per always for not being able to read rust; how does this extend to > get_task_struct()? Once you've taken a reference on current, you should > be free to pass it along to whomever. Once you take a reference on current, it becomes thread-safe. This is because taking a reference creates a value of type ARef<Task> rather than TaskRef, and ARef<Task> is considered thread-safe. Alice
