Messages in this thread | | | Date | Thu, 13 Apr 2023 08:56:18 +0000 | From | Benno Lossin <> | Subject | Re: [PATCH v4 03/13] rust: lock: introduce `Mutex` |
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On 11.04.23 07:45, Wedson Almeida Filho wrote: > From: Wedson Almeida Filho <walmeida@microsoft.com> > > This is the `struct mutex` lock backend and allows Rust code to use the > kernel mutex idiomatically. > > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Will Deacon <will@kernel.org> > Cc: Waiman Long <longman@redhat.com> > Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> > Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com> > --- > v1 -> v2: No changes > v2 -> v3: No changes > v4 -> v4: No changes > > rust/helpers.c | 7 ++ > rust/kernel/sync.rs | 1 + > rust/kernel/sync/lock.rs | 2 + > rust/kernel/sync/lock/mutex.rs | 118 +++++++++++++++++++++++++++++++++ > 4 files changed, 128 insertions(+) > create mode 100644 rust/kernel/sync/lock/mutex.rs > > diff --git a/rust/helpers.c b/rust/helpers.c > index 04b9be46e887..86af099d2d66 100644 > --- a/rust/helpers.c > +++ b/rust/helpers.c > @@ -22,6 +22,7 @@ > #include <linux/build_bug.h> > #include <linux/err.h> > #include <linux/refcount.h> > +#include <linux/mutex.h> > > __noreturn void rust_helper_BUG(void) > { > @@ -29,6 +30,12 @@ __noreturn void rust_helper_BUG(void) > } > EXPORT_SYMBOL_GPL(rust_helper_BUG); > > +void rust_helper_mutex_lock(struct mutex *lock) > +{ > + mutex_lock(lock); > +} > +EXPORT_SYMBOL_GPL(rust_helper_mutex_lock); > + > refcount_t rust_helper_REFCOUNT_INIT(int n) > { > return (refcount_t)REFCOUNT_INIT(n); > diff --git a/rust/kernel/sync.rs b/rust/kernel/sync.rs > index 81b0998eaa18..693f0b7f4e4f 100644 > --- a/rust/kernel/sync.rs > +++ b/rust/kernel/sync.rs > @@ -11,6 +11,7 @@ mod arc; > pub mod lock; > > pub use arc::{Arc, ArcBorrow, UniqueArc}; > +pub use lock::mutex::Mutex; > > /// Represents a lockdep class. It's a wrapper around C's `lock_class_key`. > #[repr(transparent)] > diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs > index 1a8ecccf4f24..98de109d9e40 100644 > --- a/rust/kernel/sync/lock.rs > +++ b/rust/kernel/sync/lock.rs > @@ -10,6 +10,8 @@ use crate::{bindings, init::PinInit, pin_init, str::CStr, types::Opaque}; > use core::{cell::UnsafeCell, marker::PhantomData, marker::PhantomPinned}; > use macros::pin_data; > > +pub mod mutex; > + > /// The "backend" of a lock. > /// > /// It is the actual implementation of the lock, without the need to repeat patterns used in all > diff --git a/rust/kernel/sync/lock/mutex.rs b/rust/kernel/sync/lock/mutex.rs > new file mode 100644 > index 000000000000..923472f04af4 > --- /dev/null > +++ b/rust/kernel/sync/lock/mutex.rs > @@ -0,0 +1,118 @@ > +// SPDX-License-Identifier: GPL-2.0 > + > +//! A kernel mutex. > +//! > +//! This module allows Rust code to use the kernel's `struct mutex`. > + > +use crate::bindings; > + > +/// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class. > +/// > +/// It uses the name if one is given, otherwise it generates one based on the file name and line > +/// number. > +#[macro_export] > +macro_rules! new_mutex { > + ($inner:expr $(, $name:literal)? $(,)?) => { > + $crate::sync::Mutex::new( > + $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!()) > + }; > +} > + > +/// A mutual exclusion primitive. > +/// > +/// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex, > +/// only one at a time is allowed to progress, the others will block (sleep) until the mutex is > +/// unlocked, at which point another thread will be allowed to wake up and make progress. > +/// > +/// Since it may block, [`Mutex`] needs to be used with care in atomic contexts. > +/// > +/// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such
The first sentence reads weird, missing another 'need'?
> +/// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros. > +/// > +/// # Examples > +/// > +/// The following example shows how to declare, allocate and initialise a struct (`Example`) that > +/// contains an inner struct (`Inner`) that is protected by a mutex. > +/// > +/// ``` > +/// use kernel::{init::InPlaceInit, init::PinInit, new_mutex, pin_init, sync::Mutex}; > +/// > +/// struct Inner { > +/// a: u32, > +/// b: u32, > +/// } > +/// > +/// #[pin_data] > +/// struct Example { > +/// c: u32, > +/// #[pin] > +/// d: Mutex<Inner>, > +/// } > +/// > +/// impl Example { > +/// fn new() -> impl PinInit<Self> { > +/// pin_init!(Self { > +/// c: 10, > +/// d <- new_mutex!(Inner { a: 20, b: 30 }), > +/// }) > +/// } > +/// } > +/// > +/// // Allocate a boxed `Example`. > +/// let e = Box::pin_init(Example::new())?; > +/// assert_eq!(e.c, 10); > +/// assert_eq!(e.d.lock().a, 20); > +/// assert_eq!(e.d.lock().b, 30); > +/// ``` > +/// > +/// The following example shows how to use interior mutability to modify the contents of a struct > +/// protected by a mutex despite only having a shared reference:
I would not bring up interior mutability here, the `Mutex` uses it, but not the user of the `Mutex`. I would just say:
To access the data behind a `Mutex`, simply take a shared reference to the `Mutex` and call `lock()` on it. This function returns a guard object that dereferences to the protected data. The `Mutex` is unlocked when the guard object goes out of scope.
> +/// > +/// ``` > +/// use kernel::sync::Mutex; > +/// > +/// struct Example { > +/// a: u32, > +/// b: u32, > +/// } > +/// > +/// fn example(m: &Mutex<Example>) { > +/// let mut guard = m.lock(); > +/// guard.a += 10; > +/// guard.b += 20; > +/// } > +/// ``` > +/// > +/// [`struct mutex`]: ../../../../include/linux/mutex.h > +pub type Mutex<T> = super::Lock<T, MutexBackend>; > + > +/// A kernel `struct mutex` lock backend. > +pub struct MutexBackend; > + > +// SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion. > +unsafe impl super::Backend for MutexBackend { > + type State = bindings::mutex; > + type GuardState = (); > + > + unsafe fn init( > + ptr: *mut Self::State, > + name: *const core::ffi::c_char, > + key: *mut bindings::lock_class_key, > + ) { > + // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and > + // `key` are valid for read indefinitely. > + unsafe { bindings::__mutex_init(ptr, name, key) } > + } > + > + unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { > + // SAFETY: The safety requirements of this function ensure that `ptr` points to valid > + // memory, and that it has been initialised before. > + unsafe { bindings::mutex_lock(ptr) }; > + } > + > + unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { > + // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the > + // caller is the owner of the mutex. > + unsafe { bindings::mutex_unlock(ptr) }; > + } > +} > -- > 2.34.1 >
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