1 // SPDX-License-Identifier: GPL-2.0 2 3 //! A kernel mutex. 4 //! 5 //! This module allows Rust code to use the kernel's `struct mutex`. 6 7 use crate::bindings; 8 9 /// Creates a [`Mutex`] 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_mutex { 15 ($inner:expr $(, $name:literal)? $(,)?) => { 16 $crate::sync::Mutex::new( 17 $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!()) 18 }; 19 } 20 pub use new_mutex; 21 22 /// A mutual exclusion primitive. 23 /// 24 /// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex, 25 /// only one at a time is allowed to progress, the others will block (sleep) until the mutex is 26 /// unlocked, at which point another thread will be allowed to wake up and make progress. 27 /// 28 /// Since it may block, [`Mutex`] needs to be used with care in atomic contexts. 29 /// 30 /// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such 31 /// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros. 32 /// 33 /// # Examples 34 /// 35 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that 36 /// contains an inner struct (`Inner`) that is protected by a mutex. 37 /// 38 /// ``` 39 /// use kernel::sync::{new_mutex, Mutex}; 40 /// 41 /// struct Inner { 42 /// a: u32, 43 /// b: u32, 44 /// } 45 /// 46 /// #[pin_data] 47 /// struct Example { 48 /// c: u32, 49 /// #[pin] 50 /// d: Mutex<Inner>, 51 /// } 52 /// 53 /// impl Example { 54 /// fn new() -> impl PinInit<Self> { 55 /// pin_init!(Self { 56 /// c: 10, 57 /// d <- new_mutex!(Inner { a: 20, b: 30 }), 58 /// }) 59 /// } 60 /// } 61 /// 62 /// // Allocate a boxed `Example`. 63 /// let e = Box::pin_init(Example::new())?; 64 /// assert_eq!(e.c, 10); 65 /// assert_eq!(e.d.lock().a, 20); 66 /// assert_eq!(e.d.lock().b, 30); 67 /// # Ok::<(), Error>(()) 68 /// ``` 69 /// 70 /// The following example shows how to use interior mutability to modify the contents of a struct 71 /// protected by a mutex despite only having a shared reference: 72 /// 73 /// ``` 74 /// use kernel::sync::Mutex; 75 /// 76 /// struct Example { 77 /// a: u32, 78 /// b: u32, 79 /// } 80 /// 81 /// fn example(m: &Mutex<Example>) { 82 /// let mut guard = m.lock(); 83 /// guard.a += 10; 84 /// guard.b += 20; 85 /// } 86 /// ``` 87 /// 88 /// [`struct mutex`]: srctree/include/linux/mutex.h 89 pub type Mutex<T> = super::Lock<T, MutexBackend>; 90 91 /// A kernel `struct mutex` lock backend. 92 pub struct MutexBackend; 93 94 // SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion. 95 unsafe impl super::Backend for MutexBackend { 96 type State = bindings::mutex; 97 type GuardState = (); 98 99 unsafe fn init( 100 ptr: *mut Self::State, 101 name: *const core::ffi::c_char, 102 key: *mut bindings::lock_class_key, 103 ) { 104 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and 105 // `key` are valid for read indefinitely. 106 unsafe { bindings::__mutex_init(ptr, name, key) } 107 } 108 109 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { 110 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid 111 // memory, and that it has been initialised before. 112 unsafe { bindings::mutex_lock(ptr) }; 113 } 114 115 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { 116 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the 117 // caller is the owner of the mutex. 118 unsafe { bindings::mutex_unlock(ptr) }; 119 } 120 } 121