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 21 /// A mutual exclusion primitive. 22 /// 23 /// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex, 24 /// only one at a time is allowed to progress, the others will block (sleep) until the mutex is 25 /// unlocked, at which point another thread will be allowed to wake up and make progress. 26 /// 27 /// Since it may block, [`Mutex`] needs to be used with care in atomic contexts. 28 /// 29 /// Instances of [`Mutex`] need a lock class and to be pinned. The recommended way to create such 30 /// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros. 31 /// 32 /// # Examples 33 /// 34 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that 35 /// contains an inner struct (`Inner`) that is protected by a mutex. 36 /// 37 /// ``` 38 /// use kernel::{init::InPlaceInit, init::PinInit, new_mutex, pin_init, sync::Mutex}; 39 /// 40 /// struct Inner { 41 /// a: u32, 42 /// b: u32, 43 /// } 44 /// 45 /// #[pin_data] 46 /// struct Example { 47 /// c: u32, 48 /// #[pin] 49 /// d: Mutex<Inner>, 50 /// } 51 /// 52 /// impl Example { 53 /// fn new() -> impl PinInit<Self> { 54 /// pin_init!(Self { 55 /// c: 10, 56 /// d <- new_mutex!(Inner { a: 20, b: 30 }), 57 /// }) 58 /// } 59 /// } 60 /// 61 /// // Allocate a boxed `Example`. 62 /// let e = Box::pin_init(Example::new())?; 63 /// assert_eq!(e.c, 10); 64 /// assert_eq!(e.d.lock().a, 20); 65 /// assert_eq!(e.d.lock().b, 30); 66 /// # Ok::<(), Error>(()) 67 /// ``` 68 /// 69 /// The following example shows how to use interior mutability to modify the contents of a struct 70 /// protected by a mutex despite only having a shared reference: 71 /// 72 /// ``` 73 /// use kernel::sync::Mutex; 74 /// 75 /// struct Example { 76 /// a: u32, 77 /// b: u32, 78 /// } 79 /// 80 /// fn example(m: &Mutex<Example>) { 81 /// let mut guard = m.lock(); 82 /// guard.a += 10; 83 /// guard.b += 20; 84 /// } 85 /// ``` 86 /// 87 /// [`struct mutex`]: ../../../../include/linux/mutex.h 88 pub type Mutex<T> = super::Lock<T, MutexBackend>; 89 90 /// A kernel `struct mutex` lock backend. 91 pub struct MutexBackend; 92 93 // SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion. 94 unsafe impl super::Backend for MutexBackend { 95 type State = bindings::mutex; 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::__mutex_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::mutex_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 mutex. 117 unsafe { bindings::mutex_unlock(ptr) }; 118 } 119 } 120