From: Oliver Mangold <[email protected]> There are types where it may both be reference counted in some cases and owned in others. In such cases, obtaining `ARef<T>` from `&T` would be unsound as it allows creation of `ARef<T>` copy from `&Owned<T>`.
Therefore, we split `AlwaysRefCounted` into `RefCounted` (which `ARef<T>` would require) and a marker trait to indicate that the type is always reference counted (and not `Ownable`) so the `&T` -> `ARef<T>` conversion is possible. - Rename `AlwaysRefCounted` to `RefCounted`. - Add a new unsafe trait `AlwaysRefCounted`. - Implement the new trait `AlwaysRefCounted` for the newly renamed `RefCounted` implementations. This leaves functionality of existing implementers of `AlwaysRefCounted` intact. Original patch by Oliver Mangold <[email protected]> [1]. Link: https://lore.kernel.org/r/[email protected] [1] Suggested-by: Alice Ryhl <[email protected]> Reviewed-by: Daniel Almeida <[email protected]> Signed-off-by: Andreas Hindborg <[email protected]> --- rust/kernel/auxiliary.rs | 7 +++++- rust/kernel/block/mq/request.rs | 15 +++++++------ rust/kernel/cred.rs | 13 ++++++++++-- rust/kernel/device.rs | 10 ++++++--- rust/kernel/device/property.rs | 7 +++++- rust/kernel/drm/device.rs | 10 ++++++--- rust/kernel/drm/gem/mod.rs | 8 ++++--- rust/kernel/fs/file.rs | 16 ++++++++++---- rust/kernel/i2c.rs | 16 +++++++++----- rust/kernel/mm.rs | 15 +++++++++---- rust/kernel/mm/mmput_async.rs | 9 ++++++-- rust/kernel/opp.rs | 10 ++++++--- rust/kernel/owned.rs | 2 +- rust/kernel/pci.rs | 10 ++++++++- rust/kernel/pid_namespace.rs | 12 +++++++++-- rust/kernel/platform.rs | 7 +++++- rust/kernel/sync/aref.rs | 47 ++++++++++++++++++++++++++--------------- rust/kernel/task.rs | 10 ++++++--- rust/kernel/types.rs | 3 ++- 19 files changed, 164 insertions(+), 63 deletions(-) diff --git a/rust/kernel/auxiliary.rs b/rust/kernel/auxiliary.rs index be76f11aecb7e..c410dcfc7b6f7 100644 --- a/rust/kernel/auxiliary.rs +++ b/rust/kernel/auxiliary.rs @@ -11,6 +11,7 @@ driver, error::{from_result, to_result, Result}, prelude::*, + sync::aref::{AlwaysRefCounted, RefCounted}, types::Opaque, ThisModule, }; @@ -283,7 +284,7 @@ unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx> kernel::impl_device_context_into_aref!(Device); // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::get_device(self.as_ref().as_raw()) }; @@ -302,6 +303,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> { fn as_ref(&self) -> &device::Device<Ctx> { // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid diff --git a/rust/kernel/block/mq/request.rs b/rust/kernel/block/mq/request.rs index ce3e30c81cb5e..cf013b9e2cacf 100644 --- a/rust/kernel/block/mq/request.rs +++ b/rust/kernel/block/mq/request.rs @@ -9,7 +9,7 @@ block::mq::Operations, error::Result, sync::{ - aref::{ARef, AlwaysRefCounted}, + aref::{ARef, AlwaysRefCounted, RefCounted}, atomic::Relaxed, Refcount, }, @@ -229,11 +229,10 @@ unsafe impl<T: Operations> Send for Request<T> {} // mutate `self` are internally synchronized` unsafe impl<T: Operations> Sync for Request<T> {} -// SAFETY: All instances of `Request<T>` are reference counted. This -// implementation of `AlwaysRefCounted` ensure that increments to the ref count -// keeps the object alive in memory at least until a matching reference count -// decrement is executed. -unsafe impl<T: Operations> AlwaysRefCounted for Request<T> { +// SAFETY: All instances of `Request<T>` are reference counted. This implementation of `RefCounted` +// ensure that increments to the ref count keeps the object alive in memory at least until a +// matching reference count decrement is executed. +unsafe impl<T: Operations> RefCounted for Request<T> { fn inc_ref(&self) { self.wrapper_ref().refcount().inc(); } @@ -255,3 +254,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull<Self>) { } } } + +// SAFETY: We currently do not implement `Ownable`, thus it is okay to obtain an `ARef<Request>` +// from a `&Request` (but this will change in the future). +unsafe impl<T: Operations> AlwaysRefCounted for Request<T> {} diff --git a/rust/kernel/cred.rs b/rust/kernel/cred.rs index ffa156b9df377..20ef0144094be 100644 --- a/rust/kernel/cred.rs +++ b/rust/kernel/cred.rs @@ -8,7 +8,12 @@ //! //! Reference: <https://www.kernel.org/doc/html/latest/security/credentials.html> -use crate::{bindings, sync::aref::AlwaysRefCounted, task::Kuid, types::Opaque}; +use crate::{ + bindings, + sync::aref::RefCounted, + task::Kuid, + types::{AlwaysRefCounted, Opaque}, +}; /// Wraps the kernel's `struct cred`. /// @@ -76,7 +81,7 @@ pub fn euid(&self) -> Kuid { } // SAFETY: The type invariants guarantee that `Credential` is always ref-counted. -unsafe impl AlwaysRefCounted for Credential { +unsafe impl RefCounted for Credential { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. @@ -90,3 +95,7 @@ unsafe fn dec_ref(obj: core::ptr::NonNull<Credential>) { unsafe { bindings::put_cred(obj.cast().as_ptr()) }; } } + +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Credential>` from a +// `&Credential`. +unsafe impl AlwaysRefCounted for Credential {} diff --git a/rust/kernel/device.rs b/rust/kernel/device.rs index 031720bf5d8ca..e09dad5f9afea 100644 --- a/rust/kernel/device.rs +++ b/rust/kernel/device.rs @@ -7,8 +7,8 @@ use crate::{ bindings, fmt, prelude::*, - sync::aref::ARef, - types::{ForeignOwnable, Opaque}, + sync::aref::{ARef, RefCounted}, + types::{AlwaysRefCounted, ForeignOwnable, Opaque}, }; use core::{any::TypeId, marker::PhantomData, ptr}; @@ -492,7 +492,7 @@ pub fn fwnode(&self) -> Option<&property::FwNode> { kernel::impl_device_context_into_aref!(Device); // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::get_device(self.as_raw()) }; @@ -504,6 +504,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + // SAFETY: As by the type invariant `Device` can be sent to any thread. unsafe impl Send for Device {} diff --git a/rust/kernel/device/property.rs b/rust/kernel/device/property.rs index 3a332a8c53a9e..a8bb824ad0ec1 100644 --- a/rust/kernel/device/property.rs +++ b/rust/kernel/device/property.rs @@ -14,6 +14,7 @@ fmt, prelude::*, str::{CStr, CString}, + sync::aref::{AlwaysRefCounted, RefCounted}, types::{ARef, Opaque}, }; @@ -359,7 +360,7 @@ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { } // SAFETY: Instances of `FwNode` are always reference-counted. -unsafe impl crate::types::AlwaysRefCounted for FwNode { +unsafe impl RefCounted for FwNode { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the // refcount is non-zero. @@ -373,6 +374,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<FwNode>` from a +// `&FwNode`. +unsafe impl AlwaysRefCounted for FwNode {} + enum Node<'a> { Borrowed(&'a FwNode), Owned(ARef<FwNode>), diff --git a/rust/kernel/drm/device.rs b/rust/kernel/drm/device.rs index 3ce8f62a00569..38ce7f389ed00 100644 --- a/rust/kernel/drm/device.rs +++ b/rust/kernel/drm/device.rs @@ -11,8 +11,8 @@ error::from_err_ptr, error::Result, prelude::*, - sync::aref::{ARef, AlwaysRefCounted}, - types::Opaque, + sync::aref::{AlwaysRefCounted, RefCounted}, + types::{ARef, Opaque}, }; use core::{alloc::Layout, mem, ops::Deref, ptr, ptr::NonNull}; @@ -198,7 +198,7 @@ fn deref(&self) -> &Self::Target { // SAFETY: DRM device objects are always reference counted and the get/put functions // satisfy the requirements. -unsafe impl<T: drm::Driver> AlwaysRefCounted for Device<T> { +unsafe impl<T: drm::Driver> RefCounted for Device<T> { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::drm_dev_get(self.as_raw()) }; @@ -213,6 +213,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Device`. +unsafe impl<T: drm::Driver> AlwaysRefCounted for Device<T> {} + impl<T: drm::Driver> AsRef<device::Device> for Device<T> { fn as_ref(&self) -> &device::Device { // SAFETY: `bindings::drm_device::dev` is valid as long as the DRM device itself is valid, diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs index a7f682e95c018..ad6840a440165 100644 --- a/rust/kernel/drm/gem/mod.rs +++ b/rust/kernel/drm/gem/mod.rs @@ -10,8 +10,7 @@ drm::driver::{AllocImpl, AllocOps}, error::{to_result, Result}, prelude::*, - sync::aref::{ARef, AlwaysRefCounted}, - types::Opaque, + types::{ARef, AlwaysRefCounted, Opaque}, }; use core::{ops::Deref, ptr::NonNull}; @@ -253,7 +252,7 @@ extern "C" fn free_callback(obj: *mut bindings::drm_gem_object) { } // SAFETY: Instances of `Object<T>` are always reference-counted. -unsafe impl<T: DriverObject> crate::types::AlwaysRefCounted for Object<T> { +unsafe impl<T: DriverObject> crate::types::RefCounted for Object<T> { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::drm_gem_object_get(self.as_raw()) }; @@ -267,6 +266,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) { unsafe { bindings::drm_gem_object_put(obj.as_raw()) } } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Object`. +unsafe impl<T: DriverObject> crate::types::AlwaysRefCounted for Object<T> {} impl<T: DriverObject> super::private::Sealed for Object<T> {} diff --git a/rust/kernel/fs/file.rs b/rust/kernel/fs/file.rs index 23ee689bd2400..06e457d62a939 100644 --- a/rust/kernel/fs/file.rs +++ b/rust/kernel/fs/file.rs @@ -12,8 +12,8 @@ cred::Credential, error::{code::*, to_result, Error, Result}, fmt, - sync::aref::{ARef, AlwaysRefCounted}, - types::{NotThreadSafe, Opaque}, + sync::aref::RefCounted, + types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque}, }; use core::ptr; @@ -197,7 +197,7 @@ unsafe impl Sync for File {} // SAFETY: The type invariants guarantee that `File` is always ref-counted. This implementation // makes `ARef<File>` own a normal refcount. -unsafe impl AlwaysRefCounted for File { +unsafe impl RefCounted for File { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. @@ -212,6 +212,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<File>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<File>` from a +// `&File`. +unsafe impl AlwaysRefCounted for File {} + /// Wraps the kernel's `struct file`. Not thread safe. /// /// This type represents a file that is not known to be safe to transfer across thread boundaries. @@ -233,7 +237,7 @@ pub struct LocalFile { // SAFETY: The type invariants guarantee that `LocalFile` is always ref-counted. This implementation // makes `ARef<LocalFile>` own a normal refcount. -unsafe impl AlwaysRefCounted for LocalFile { +unsafe impl RefCounted for LocalFile { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. @@ -249,6 +253,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<LocalFile>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<LocalFile>` from a +// `&LocalFile`. +unsafe impl AlwaysRefCounted for LocalFile {} + impl LocalFile { /// Constructs a new `struct file` wrapper from a file descriptor. /// diff --git a/rust/kernel/i2c.rs b/rust/kernel/i2c.rs index 39b0a9a207fda..b5e3c236a5c16 100644 --- a/rust/kernel/i2c.rs +++ b/rust/kernel/i2c.rs @@ -17,8 +17,10 @@ of, prelude::*, types::{ + ARef, AlwaysRefCounted, - Opaque, // + Opaque, + RefCounted, // }, // }; @@ -31,8 +33,6 @@ }, // }; -use kernel::types::ARef; - /// An I2C device id table. #[repr(transparent)] #[derive(Clone, Copy)] @@ -416,7 +416,7 @@ pub fn get(index: i32) -> Result<ARef<Self>> { kernel::impl_device_context_into_aref!(I2cAdapter); // SAFETY: Instances of `I2cAdapter` are always reference-counted. -unsafe impl crate::types::AlwaysRefCounted for I2cAdapter { +unsafe impl crate::types::RefCounted for I2cAdapter { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::i2c_get_adapter(self.index()) }; @@ -427,6 +427,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) { unsafe { bindings::i2c_put_adapter(obj.as_ref().as_raw()) } } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from an +// `&I2cAdapter`. +unsafe impl AlwaysRefCounted for I2cAdapter {} /// The i2c board info representation /// @@ -492,7 +495,7 @@ unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for I2cClient<C kernel::impl_device_context_into_aref!(I2cClient); // SAFETY: Instances of `I2cClient` are always reference-counted. -unsafe impl AlwaysRefCounted for I2cClient { +unsafe impl RefCounted for I2cClient { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::get_device(self.as_ref().as_raw()) }; @@ -503,6 +506,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) { unsafe { bindings::put_device(&raw mut (*obj.as_ref().as_raw()).dev) } } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from an +// `&I2cClient`. +unsafe impl AlwaysRefCounted for I2cClient {} impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for I2cClient<Ctx> { fn as_ref(&self) -> &device::Device<Ctx> { diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs index 4764d7b68f2a7..dd9e3969e7206 100644 --- a/rust/kernel/mm.rs +++ b/rust/kernel/mm.rs @@ -13,8 +13,8 @@ use crate::{ bindings, - sync::aref::{ARef, AlwaysRefCounted}, - types::{NotThreadSafe, Opaque}, + sync::aref::RefCounted, + types::{ARef, AlwaysRefCounted, NotThreadSafe, Opaque}, }; use core::{ops::Deref, ptr::NonNull}; @@ -55,7 +55,7 @@ unsafe impl Send for Mm {} unsafe impl Sync for Mm {} // SAFETY: By the type invariants, this type is always refcounted. -unsafe impl AlwaysRefCounted for Mm { +unsafe impl RefCounted for Mm { #[inline] fn inc_ref(&self) { // SAFETY: The pointer is valid since self is a reference. @@ -69,6 +69,9 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Mm>` from a `&Mm`. +unsafe impl AlwaysRefCounted for Mm {} + /// A wrapper for the kernel's `struct mm_struct`. /// /// This type is like [`Mm`], but with non-zero `mm_users`. It can only be used when `mm_users` can @@ -91,7 +94,7 @@ unsafe impl Send for MmWithUser {} unsafe impl Sync for MmWithUser {} // SAFETY: By the type invariants, this type is always refcounted. -unsafe impl AlwaysRefCounted for MmWithUser { +unsafe impl RefCounted for MmWithUser { #[inline] fn inc_ref(&self) { // SAFETY: The pointer is valid since self is a reference. @@ -105,6 +108,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<MmWithUser>` from a +// `&MmWithUser`. +unsafe impl AlwaysRefCounted for MmWithUser {} + // Make all `Mm` methods available on `MmWithUser`. impl Deref for MmWithUser { type Target = Mm; diff --git a/rust/kernel/mm/mmput_async.rs b/rust/kernel/mm/mmput_async.rs index b8d2f051225c7..aba4ce675c860 100644 --- a/rust/kernel/mm/mmput_async.rs +++ b/rust/kernel/mm/mmput_async.rs @@ -10,7 +10,8 @@ use crate::{ bindings, mm::MmWithUser, - sync::aref::{ARef, AlwaysRefCounted}, + sync::aref::RefCounted, + types::{ARef, AlwaysRefCounted}, }; use core::{ops::Deref, ptr::NonNull}; @@ -34,7 +35,7 @@ unsafe impl Send for MmWithUserAsync {} unsafe impl Sync for MmWithUserAsync {} // SAFETY: By the type invariants, this type is always refcounted. -unsafe impl AlwaysRefCounted for MmWithUserAsync { +unsafe impl RefCounted for MmWithUserAsync { #[inline] fn inc_ref(&self) { // SAFETY: The pointer is valid since self is a reference. @@ -48,6 +49,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<MmWithUserAsync>` +// from a `&MmWithUserAsync`. +unsafe impl AlwaysRefCounted for MmWithUserAsync {} + // Make all `MmWithUser` methods available on `MmWithUserAsync`. impl Deref for MmWithUserAsync { type Target = MmWithUser; diff --git a/rust/kernel/opp.rs b/rust/kernel/opp.rs index a760fac287655..06fe2ca776a4f 100644 --- a/rust/kernel/opp.rs +++ b/rust/kernel/opp.rs @@ -16,8 +16,8 @@ ffi::{c_char, c_ulong}, prelude::*, str::CString, - sync::aref::{ARef, AlwaysRefCounted}, - types::Opaque, + sync::aref::RefCounted, + types::{ARef, AlwaysRefCounted, Opaque}, }; #[cfg(CONFIG_CPU_FREQ)] @@ -1041,7 +1041,7 @@ unsafe impl Send for OPP {} unsafe impl Sync for OPP {} /// SAFETY: The type invariants guarantee that [`OPP`] is always refcounted. -unsafe impl AlwaysRefCounted for OPP { +unsafe impl RefCounted for OPP { fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. unsafe { bindings::dev_pm_opp_get(self.0.get()) }; @@ -1053,6 +1053,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<OPP>` from an +// `&OPP`. +unsafe impl AlwaysRefCounted for OPP {} + impl OPP { /// Creates an owned reference to a [`OPP`] from a valid pointer. /// diff --git a/rust/kernel/owned.rs b/rust/kernel/owned.rs index fe30580331df9..b02edda11fcf6 100644 --- a/rust/kernel/owned.rs +++ b/rust/kernel/owned.rs @@ -25,7 +25,7 @@ /// /// Note: The underlying object is not required to provide internal reference counting, because it /// represents a unique, owned reference. If reference counting (on the Rust side) is required, -/// [`AlwaysRefCounted`](crate::types::AlwaysRefCounted) should be implemented. +/// [`RefCounted`](crate::types::RefCounted) should be implemented. /// /// # Safety /// diff --git a/rust/kernel/pci.rs b/rust/kernel/pci.rs index bea76ca9c3da5..9ee8f2bc6db9e 100644 --- a/rust/kernel/pci.rs +++ b/rust/kernel/pci.rs @@ -19,6 +19,10 @@ }, prelude::*, str::CStr, + sync::aref::{ + AlwaysRefCounted, + RefCounted, // + }, types::Opaque, ThisModule, // }; @@ -467,7 +471,7 @@ unsafe impl<Ctx: device::DeviceContext> device::AsBusDevice<Ctx> for Device<Ctx> impl crate::dma::Device for Device<device::Core> {} // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::pci_dev_get(self.as_raw()) }; @@ -479,6 +483,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> { fn as_ref(&self) -> &device::Device<Ctx> { // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs index 979a9718f153d..4f6a94540e33d 100644 --- a/rust/kernel/pid_namespace.rs +++ b/rust/kernel/pid_namespace.rs @@ -7,7 +7,11 @@ //! C header: [`include/linux/pid_namespace.h`](srctree/include/linux/pid_namespace.h) and //! [`include/linux/pid.h`](srctree/include/linux/pid.h) -use crate::{bindings, sync::aref::AlwaysRefCounted, types::Opaque}; +use crate::{ + bindings, + sync::aref::RefCounted, + types::{AlwaysRefCounted, Opaque}, +}; use core::ptr; /// Wraps the kernel's `struct pid_namespace`. Thread safe. @@ -41,7 +45,7 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_namespace) -> &'a Self { } // SAFETY: Instances of `PidNamespace` are always reference-counted. -unsafe impl AlwaysRefCounted for PidNamespace { +unsafe impl RefCounted for PidNamespace { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. @@ -55,6 +59,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<PidNamespace>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<PidNamespace>` from +// a `&PidNamespace`. +unsafe impl AlwaysRefCounted for PidNamespace {} + // SAFETY: // - `PidNamespace::dec_ref` can be called from any thread. // - It is okay to send ownership of `PidNamespace` across thread boundaries. diff --git a/rust/kernel/platform.rs b/rust/kernel/platform.rs index 35a5813ffb33f..139517c21961e 100644 --- a/rust/kernel/platform.rs +++ b/rust/kernel/platform.rs @@ -13,6 +13,7 @@ irq::{self, IrqRequest}, of, prelude::*, + sync::aref::{AlwaysRefCounted, RefCounted}, types::Opaque, ThisModule, }; @@ -490,7 +491,7 @@ pub fn optional_irq_by_name(&self, name: &CStr) -> Result<IrqRequest<'_>> { impl crate::dma::Device for Device<device::Core> {} // SAFETY: Instances of `Device` are always reference-counted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Device { +unsafe impl RefCounted for Device { fn inc_ref(&self) { // SAFETY: The existence of a shared reference guarantees that the refcount is non-zero. unsafe { bindings::get_device(self.as_ref().as_raw()) }; @@ -502,6 +503,10 @@ unsafe fn dec_ref(obj: NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Device>` from a +// `&Device`. +unsafe impl AlwaysRefCounted for Device {} + impl<Ctx: device::DeviceContext> AsRef<device::Device<Ctx>> for Device<Ctx> { fn as_ref(&self) -> &device::Device<Ctx> { // SAFETY: By the type invariant of `Self`, `self.as_raw()` is a pointer to a valid diff --git a/rust/kernel/sync/aref.rs b/rust/kernel/sync/aref.rs index e175aefe86151..61caddfd89619 100644 --- a/rust/kernel/sync/aref.rs +++ b/rust/kernel/sync/aref.rs @@ -19,11 +19,9 @@ use core::{marker::PhantomData, mem::ManuallyDrop, ops::Deref, ptr::NonNull}; -/// Types that are _always_ reference counted. +/// Types that are internally reference counted. /// /// It allows such types to define their own custom ref increment and decrement functions. -/// Additionally, it allows users to convert from a shared reference `&T` to an owned reference -/// [`ARef<T>`]. /// /// This is usually implemented by wrappers to existing structures on the C side of the code. For /// Rust code, the recommendation is to use [`Arc`](crate::sync::Arc) to create reference-counted @@ -40,9 +38,8 @@ /// at least until matching decrements are performed. /// /// Implementers must also ensure that all instances are reference-counted. (Otherwise they -/// won't be able to honour the requirement that [`AlwaysRefCounted::inc_ref`] keep the object -/// alive.) -pub unsafe trait AlwaysRefCounted { +/// won't be able to honour the requirement that [`RefCounted::inc_ref`] keep the object alive.) +pub unsafe trait RefCounted { /// Increments the reference count on the object. fn inc_ref(&self); @@ -55,11 +52,27 @@ pub unsafe trait AlwaysRefCounted { /// Callers must ensure that there was a previous matching increment to the reference count, /// and that the object is no longer used after its reference count is decremented (as it may /// result in the object being freed), unless the caller owns another increment on the refcount - /// (e.g., it calls [`AlwaysRefCounted::inc_ref`] twice, then calls - /// [`AlwaysRefCounted::dec_ref`] once). + /// (e.g., it calls [`RefCounted::inc_ref`] twice, then calls [`RefCounted::dec_ref`] once). unsafe fn dec_ref(obj: NonNull<Self>); } +/// Always reference-counted type. +/// +/// It allows deriving a counted reference [`ARef<T>`] from a `&T`. +/// +/// This provides some convenience, but it allows "escaping" borrow checks on `&T`. As it +/// complicates attempts to ensure that a reference to T is unique, it is optional to provide for +/// [`RefCounted`] types. See *Safety* below. +/// +/// # Safety +/// +/// Implementers must ensure that no safety invariants are violated by upgrading an `&T` to an +/// [`ARef<T>`]. In particular that implies [`AlwaysRefCounted`] and [`crate::types::Ownable`] +/// cannot be implemented for the same type, as this would allow violating the uniqueness guarantee +/// of [`crate::types::Owned<T>`] by dereferencing it into an `&T` and obtaining an [`ARef`] from +/// that. +pub unsafe trait AlwaysRefCounted: RefCounted {} + /// An owned reference to an always-reference-counted object. /// /// The object's reference count is automatically decremented when an instance of [`ARef`] is @@ -70,7 +83,7 @@ pub unsafe trait AlwaysRefCounted { /// /// The pointer stored in `ptr` is non-null and valid for the lifetime of the [`ARef`] instance. In /// particular, the [`ARef`] instance owns an increment on the underlying object's reference count. -pub struct ARef<T: AlwaysRefCounted> { +pub struct ARef<T: RefCounted> { ptr: NonNull<T>, _p: PhantomData<T>, } @@ -79,16 +92,16 @@ pub struct ARef<T: AlwaysRefCounted> { // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs // `T` to be `Send` because any thread that has an `ARef<T>` may ultimately access `T` using a // mutable reference, for example, when the reference count reaches zero and `T` is dropped. -unsafe impl<T: AlwaysRefCounted + Sync + Send> Send for ARef<T> {} +unsafe impl<T: RefCounted + Sync + Send> Send for ARef<T> {} // SAFETY: It is safe to send `&ARef<T>` to another thread when the underlying `T` is `Sync` // because it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, // it needs `T` to be `Send` because any thread that has a `&ARef<T>` may clone it and get an // `ARef<T>` on that thread, so the thread may ultimately access `T` using a mutable reference, for // example, when the reference count reaches zero and `T` is dropped. -unsafe impl<T: AlwaysRefCounted + Sync + Send> Sync for ARef<T> {} +unsafe impl<T: RefCounted + Sync + Send> Sync for ARef<T> {} -impl<T: AlwaysRefCounted> ARef<T> { +impl<T: RefCounted> ARef<T> { /// Creates a new instance of [`ARef`]. /// /// It takes over an increment of the reference count on the underlying object. @@ -117,12 +130,12 @@ pub unsafe fn from_raw(ptr: NonNull<T>) -> Self { /// /// ``` /// use core::ptr::NonNull; - /// use kernel::sync::aref::{ARef, AlwaysRefCounted}; + /// use kernel::sync::aref::{ARef, RefCounted}; /// /// struct Empty {} /// /// # // SAFETY: TODO. - /// unsafe impl AlwaysRefCounted for Empty { + /// unsafe impl RefCounted for Empty { /// fn inc_ref(&self) {} /// unsafe fn dec_ref(_obj: NonNull<Self>) {} /// } @@ -140,7 +153,7 @@ pub fn into_raw(me: Self) -> NonNull<T> { } } -impl<T: AlwaysRefCounted> Clone for ARef<T> { +impl<T: RefCounted> Clone for ARef<T> { fn clone(&self) -> Self { self.inc_ref(); // SAFETY: We just incremented the refcount above. @@ -148,7 +161,7 @@ fn clone(&self) -> Self { } } -impl<T: AlwaysRefCounted> Deref for ARef<T> { +impl<T: RefCounted> Deref for ARef<T> { type Target = T; fn deref(&self) -> &Self::Target { @@ -165,7 +178,7 @@ fn from(b: &T) -> Self { } } -impl<T: AlwaysRefCounted> Drop for ARef<T> { +impl<T: RefCounted> Drop for ARef<T> { fn drop(&mut self) { // SAFETY: The type invariants guarantee that the `ARef` owns the reference we're about to // decrement. diff --git a/rust/kernel/task.rs b/rust/kernel/task.rs index 49fad6de06740..0a6e38d984560 100644 --- a/rust/kernel/task.rs +++ b/rust/kernel/task.rs @@ -9,8 +9,8 @@ ffi::{c_int, c_long, c_uint}, mm::MmWithUser, pid_namespace::PidNamespace, - sync::aref::ARef, - types::{NotThreadSafe, Opaque}, + sync::aref::{AlwaysRefCounted, RefCounted}, + types::{ARef, NotThreadSafe, Opaque}, }; use core::{ cmp::{Eq, PartialEq}, @@ -348,7 +348,7 @@ pub fn active_pid_ns(&self) -> Option<&PidNamespace> { } // SAFETY: The type invariants guarantee that `Task` is always refcounted. -unsafe impl crate::sync::aref::AlwaysRefCounted for Task { +unsafe impl RefCounted for Task { #[inline] fn inc_ref(&self) { // SAFETY: The existence of a shared reference means that the refcount is nonzero. @@ -362,6 +362,10 @@ unsafe fn dec_ref(obj: ptr::NonNull<Self>) { } } +// SAFETY: We do not implement `Ownable`, thus it is okay to obtain an `ARef<Task>` from a +// `&Task`. +unsafe impl AlwaysRefCounted for Task {} + impl Kuid { /// Get the current euid. #[inline] diff --git a/rust/kernel/types.rs b/rust/kernel/types.rs index 4aec7b699269a..9b96aa2ebdb7e 100644 --- a/rust/kernel/types.rs +++ b/rust/kernel/types.rs @@ -18,7 +18,8 @@ }, sync::aref::{ ARef, - AlwaysRefCounted, // + AlwaysRefCounted, + RefCounted, // }, // }; -- 2.51.2
