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 /// Creates a [`Mutex`] 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_mutex { 13 ($inner:expr $(, $name:literal)? $(,)?) => { 14 $crate::sync::Mutex::new( 15 $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!()) 16 }; 17 } 18 pub use new_mutex; 19 20 /// A mutual exclusion primitive. 21 /// 22 /// Exposes the kernel's [`struct mutex`]. When multiple threads attempt to lock the same mutex, 23 /// only one at a time is allowed to progress, the others will block (sleep) until the mutex is 24 /// unlocked, at which point another thread will be allowed to wake up and make progress. 25 /// 26 /// Since it may block, [`Mutex`] needs to be used with care in atomic contexts. 27 /// 28 /// Instances of [`Mutex`] 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_mutex`] 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 mutex. 35 /// 36 /// ``` 37 /// use kernel::sync::{new_mutex, Mutex}; 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: Mutex<Inner>, 49 /// } 50 /// 51 /// impl Example { 52 /// fn new() -> impl PinInit<Self> { 53 /// pin_init!(Self { 54 /// c: 10, 55 /// d <- new_mutex!(Inner { a: 20, b: 30 }), 56 /// }) 57 /// } 58 /// } 59 /// 60 /// // Allocate a boxed `Example`. 61 /// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?; 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 mutex despite only having a shared reference: 70 /// 71 /// ``` 72 /// use kernel::sync::Mutex; 73 /// 74 /// struct Example { 75 /// a: u32, 76 /// b: u32, 77 /// } 78 /// 79 /// fn example(m: &Mutex<Example>) { 80 /// let mut guard = m.lock(); 81 /// guard.a += 10; 82 /// guard.b += 20; 83 /// } 84 /// ``` 85 /// 86 /// [`struct mutex`]: srctree/include/linux/mutex.h 87 pub type Mutex<T> = super::Lock<T, MutexBackend>; 88 89 /// A [`Guard`] acquired from locking a [`Mutex`]. 90 /// 91 /// This is simply a type alias for a [`Guard`] returned from locking a [`Mutex`]. It will unlock 92 /// the [`Mutex`] upon being dropped. 93 /// 94 /// [`Guard`]: super::Guard 95 pub type MutexGuard<'a, T> = super::Guard<'a, T, MutexBackend>; 96 97 /// A kernel `struct mutex` lock backend. 98 pub struct MutexBackend; 99 100 // SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion. 101 unsafe impl super::Backend for MutexBackend { 102 type State = bindings::mutex; 103 type GuardState = (); 104 105 unsafe fn init( 106 ptr: *mut Self::State, 107 name: *const crate::ffi::c_char, 108 key: *mut bindings::lock_class_key, 109 ) { 110 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and 111 // `key` are valid for read indefinitely. 112 unsafe { bindings::__mutex_init(ptr, name, key) } 113 } 114 115 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState { 116 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid 117 // memory, and that it has been initialised before. 118 unsafe { bindings::mutex_lock(ptr) }; 119 } 120 121 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) { 122 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the 123 // caller is the owner of the mutex. 124 unsafe { bindings::mutex_unlock(ptr) }; 125 } 126 127 unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> { 128 // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use. 129 let result = unsafe { bindings::mutex_trylock(ptr) }; 130 131 if result != 0 { 132 Some(()) 133 } else { 134 None 135 } 136 } 137 138 unsafe fn assert_is_held(ptr: *mut Self::State) { 139 // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use. 140 unsafe { bindings::mutex_assert_is_held(ptr) } 141 } 142 } 143