| Message ID | 20240725-alice-file-v8-1-55a2e80deaa8@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | File abstractions needed by Rust Binder | expand |
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@proton.me> > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > Reviewed-by: Trevor Gross <tmgross@umich.edu> > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > --- > 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.
On Thu, Jul 25, 2024 at 4:37 PM Peter Zijlstra <peterz@infradead.org> 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@proton.me> > > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > > Reviewed-by: Trevor Gross <tmgross@umich.edu> > > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > > Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com> > > Signed-off-by: Alice Ryhl <aliceryhl@google.com> > > --- > > 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
On Thu, Jul 25, 2024 at 05:09:14PM +0200, Alice Ryhl wrote: > > 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. Ignoring comments, there isn't a single mention of ARef there. Where does it come from?
On Thu, Jul 25, 2024 at 5:30 PM Peter Zijlstra <peterz@infradead.org> wrote: > > On Thu, Jul 25, 2024 at 05:09:14PM +0200, Alice Ryhl wrote: > > > > 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. > > Ignoring comments, there isn't a single mention of ARef there. Where > does it come from? That's because the conversion to ARef<Task> is a two-step process. The TaskRef type just provides a conversion from &TaskRef to &Task via the `impl Deref` block. There is a conversion from &Task to ARef<Task> elsewhere, and this conversion is where the call to get_task_struct() happens. Alice
On Thu, 25 Jul 2024 14:27:34 +0000 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 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@proton.me> > Reviewed-by: Benno Lossin <benno.lossin@proton.me> > Reviewed-by: Trevor Gross <tmgross@umich.edu> > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > Reviewed-by: Björn Roy Baron <bjorn3_gh@protonmail.com> > Signed-off-by: Alice Ryhl <aliceryhl@google.com> Reviewed-by: Gary Guo <gary@garyguo.net> > --- > 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, } } diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index bd189d646adb..bb115d730ebb 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -473,3 +473,24 @@ unsafe impl AsBytes for str {} // does not have any uninitialized portions either. unsafe impl<T: AsBytes> AsBytes for [T] {} unsafe impl<T: AsBytes, const N: usize> AsBytes for [T; N] {} + +/// 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. +/// +/// This type also makes the type `!Sync`, which prevents immutable access to the value from +/// several threads in parallel. +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;