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 pub use new_spinlock; 21 22 /// A spinlock. 23 /// 24 /// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only 25 /// one at a time is allowed to progress, the others will block (spinning) until the spinlock is 26 /// unlocked, at which point another CPU will be allowed to make progress. 27 /// 28 /// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such 29 /// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros. 30 /// 31 /// # Examples 32 /// 33 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that 34 /// contains an inner struct (`Inner`) that is protected by a spinlock. 35 /// 36 /// ``` 37 /// use kernel::sync::{new_spinlock, SpinLock}; 38 /// 39 /// struct Inner { 40 /// a: u32, 41 /// b: u32, 42 /// } 43 /// 44 /// #[pin_data] 45 /// struct Example { 46 /// c: u32, 47 /// #[pin] 48 /// d: SpinLock<Inner>, 49 /// } 50 /// 51 /// impl Example { 52 /// fn new() -> impl PinInit<Self> { 53 /// pin_init!(Self { 54 /// c: 10, 55 /// d <- new_spinlock!(Inner { a: 20, b: 30 }), 56 /// }) 57 /// } 58 /// } 59 /// 60 /// // Allocate a boxed `Example`. 61 /// let e = Box::pin_init(Example::new())?; 62 /// assert_eq!(e.c, 10); 63 /// assert_eq!(e.d.lock().a, 20); 64 /// assert_eq!(e.d.lock().b, 30); 65 /// # Ok::<(), Error>(()) 66 /// ``` 67 /// 68 /// The following example shows how to use interior mutability to modify the contents of a struct 69 /// protected by a spinlock despite only having a shared reference: 70 /// 71 /// ``` 72 /// use kernel::sync::SpinLock; 73 /// 74 /// struct Example { 75 /// a: u32, 76 /// b: u32, 77 /// } 78 /// 79 /// fn example(m: &SpinLock<Example>) { 80 /// let mut guard = m.lock(); 81 /// guard.a += 10; 82 /// guard.b += 20; 83 /// } 84 /// ``` 85 /// 86 /// [`spinlock_t`]: srctree/include/linux/spinlock.h 87 pub type SpinLock<T> = super::Lock<T, SpinLockBackend>; 88 89 /// A kernel `spinlock_t` lock backend. 90 pub struct SpinLockBackend; 91 92 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the 93 // default implementation that always calls the same locking method. 94 unsafe impl super::Backend for SpinLockBackend { 95 type State = bindings::spinlock_t; 96 type GuardState = (); 97 98 unsafe fn init( 99 ptr: *mut Self::State, 100 name: *const core::ffi::c_char, 101 key: *mut bindings::lock_class_key, 102 ) { 103 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and 104 // `key` are valid for read indefinitely. 105 unsafe { bindings::__spin_lock_init(ptr, name, key) } 106 } 107 108 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { 109 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid 110 // memory, and that it has been initialised before. 111 unsafe { bindings::spin_lock(ptr) } 112 } 113 114 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { 115 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the 116 // caller is the owner of the spinlock. 117 unsafe { bindings::spin_unlock(ptr) } 118 } 119 } 120