1 // SPDX-License-Identifier: GPL-2.0 2 3 //! A kernel spinlock. 4 //! 5 //! This module allows Rust code to use the kernel's `spinlock_t`. 6 7 use crate::bindings; 8 9 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class. 10 /// 11 /// It uses the name if one is given, otherwise it generates one based on the file name and line 12 /// number. 13 #[macro_export] 14 macro_rules! new_spinlock { 15 ($inner:expr $(, $name:literal)? $(,)?) => { 16 $crate::sync::SpinLock::new( 17 $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!()) 18 }; 19 } 20 21 /// A spinlock. 22 /// 23 /// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only 24 /// one at a time is allowed to progress, the others will block (spinning) until the spinlock is 25 /// unlocked, at which point another CPU will be allowed to make progress. 26 /// 27 /// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such 28 /// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros. 29 /// 30 /// # Examples 31 /// 32 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that 33 /// contains an inner struct (`Inner`) that is protected by a spinlock. 34 /// 35 /// ``` 36 /// use kernel::{init::InPlaceInit, init::PinInit, new_spinlock, pin_init, sync::SpinLock}; 37 /// 38 /// struct Inner { 39 /// a: u32, 40 /// b: u32, 41 /// } 42 /// 43 /// #[pin_data] 44 /// struct Example { 45 /// c: u32, 46 /// #[pin] 47 /// d: SpinLock<Inner>, 48 /// } 49 /// 50 /// impl Example { 51 /// fn new() -> impl PinInit<Self> { 52 /// pin_init!(Self { 53 /// c: 10, 54 /// d <- new_spinlock!(Inner { a: 20, b: 30 }), 55 /// }) 56 /// } 57 /// } 58 /// 59 /// // Allocate a boxed `Example`. 60 /// let e = Box::pin_init(Example::new())?; 61 /// assert_eq!(e.c, 10); 62 /// assert_eq!(e.d.lock().a, 20); 63 /// assert_eq!(e.d.lock().b, 30); 64 /// # Ok::<(), Error>(()) 65 /// ``` 66 /// 67 /// The following example shows how to use interior mutability to modify the contents of a struct 68 /// protected by a spinlock despite only having a shared reference: 69 /// 70 /// ``` 71 /// use kernel::sync::SpinLock; 72 /// 73 /// struct Example { 74 /// a: u32, 75 /// b: u32, 76 /// } 77 /// 78 /// fn example(m: &SpinLock<Example>) { 79 /// let mut guard = m.lock(); 80 /// guard.a += 10; 81 /// guard.b += 20; 82 /// } 83 /// ``` 84 /// 85 /// [`spinlock_t`]: ../../../../include/linux/spinlock.h 86 pub type SpinLock<T> = super::Lock<T, SpinLockBackend>; 87 88 /// A kernel `spinlock_t` lock backend. 89 pub struct SpinLockBackend; 90 91 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the 92 // default implementation that always calls the same locking method. 93 unsafe impl super::Backend for SpinLockBackend { 94 type State = bindings::spinlock_t; 95 type GuardState = (); 96 97 unsafe fn init( 98 ptr: *mut Self::State, 99 name: *const core::ffi::c_char, 100 key: *mut bindings::lock_class_key, 101 ) { 102 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and 103 // `key` are valid for read indefinitely. 104 unsafe { bindings::__spin_lock_init(ptr, name, key) } 105 } 106 107 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { 108 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid 109 // memory, and that it has been initialised before. 110 unsafe { bindings::spin_lock(ptr) } 111 } 112 113 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { 114 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the 115 // caller is the owner of the mutex. 116 unsafe { bindings::spin_unlock(ptr) } 117 } 118 } 119