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 /// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class. 8 /// 9 /// It uses the name if one is given, otherwise it generates one based on the file name and line 10 /// number. 11 #[macro_export] 12 macro_rules! new_spinlock { 13 ($inner:expr $(, $name:literal)? $(,)?) => { 14 $crate::sync::SpinLock::new( 15 $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!()) 16 }; 17 } 18 pub use new_spinlock; 19 20 /// A spinlock. 21 /// 22 /// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only 23 /// one at a time is allowed to progress, the others will block (spinning) until the spinlock is 24 /// unlocked, at which point another CPU will be allowed to make progress. 25 /// 26 /// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such 27 /// instances is with the [`pin_init`](crate::pin_init) and [`new_spinlock`] macros. 28 /// 29 /// # Examples 30 /// 31 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that 32 /// contains an inner struct (`Inner`) that is protected by a spinlock. 33 /// 34 /// ``` 35 /// use kernel::sync::{new_spinlock, SpinLock}; 36 /// 37 /// struct Inner { 38 /// a: u32, 39 /// b: u32, 40 /// } 41 /// 42 /// #[pin_data] 43 /// struct Example { 44 /// c: u32, 45 /// #[pin] 46 /// d: SpinLock<Inner>, 47 /// } 48 /// 49 /// impl Example { 50 /// fn new() -> impl PinInit<Self> { 51 /// pin_init!(Self { 52 /// c: 10, 53 /// d <- new_spinlock!(Inner { a: 20, b: 30 }), 54 /// }) 55 /// } 56 /// } 57 /// 58 /// // Allocate a boxed `Example`. 59 /// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?; 60 /// assert_eq!(e.c, 10); 61 /// assert_eq!(e.d.lock().a, 20); 62 /// assert_eq!(e.d.lock().b, 30); 63 /// # Ok::<(), Error>(()) 64 /// ``` 65 /// 66 /// The following example shows how to use interior mutability to modify the contents of a struct 67 /// protected by a spinlock despite only having a shared reference: 68 /// 69 /// ``` 70 /// use kernel::sync::SpinLock; 71 /// 72 /// struct Example { 73 /// a: u32, 74 /// b: u32, 75 /// } 76 /// 77 /// fn example(m: &SpinLock<Example>) { 78 /// let mut guard = m.lock(); 79 /// guard.a += 10; 80 /// guard.b += 20; 81 /// } 82 /// ``` 83 /// 84 /// [`spinlock_t`]: srctree/include/linux/spinlock.h 85 pub type SpinLock<T> = super::Lock<T, SpinLockBackend>; 86 87 /// A kernel `spinlock_t` lock backend. 88 pub struct SpinLockBackend; 89 90 // SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the 91 // default implementation that always calls the same locking method. 92 unsafe impl super::Backend for SpinLockBackend { 93 type State = bindings::spinlock_t; 94 type GuardState = (); 95 96 unsafe fn init( 97 ptr: *mut Self::State, 98 name: *const crate::ffi::c_char, 99 key: *mut bindings::lock_class_key, 100 ) { 101 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and 102 // `key` are valid for read indefinitely. 103 unsafe { bindings::__spin_lock_init(ptr, name, key) } 104 } 105 106 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { 107 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid 108 // memory, and that it has been initialised before. 109 unsafe { bindings::spin_lock(ptr) } 110 } 111 112 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { 113 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the 114 // caller is the owner of the spinlock. 115 unsafe { bindings::spin_unlock(ptr) } 116 } 117 118 unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> { 119 // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use. 120 let result = unsafe { bindings::spin_trylock(ptr) }; 121 122 if result != 0 { 123 Some(()) 124 } else { 125 None 126 } 127 } 128 } 129