1 // SPDX-License-Identifier: GPL-2.0 1 // SPDX-License-Identifier: GPL-2.0
2 2
3 //! A kernel mutex. 3 //! A kernel mutex.
4 //! 4 //!
5 //! This module allows Rust code to use the ke 5 //! This module allows Rust code to use the kernel's `struct mutex`.
6 6
7 /// Creates a [`Mutex`] initialiser with the g 7 /// Creates a [`Mutex`] initialiser with the given name and a newly-created lock class.
8 /// 8 ///
9 /// It uses the name if one is given, otherwis 9 /// It uses the name if one is given, otherwise it generates one based on the file name and line
10 /// number. 10 /// number.
11 #[macro_export] 11 #[macro_export]
12 macro_rules! new_mutex { 12 macro_rules! new_mutex {
13 ($inner:expr $(, $name:literal)? $(,)?) => 13 ($inner:expr $(, $name:literal)? $(,)?) => {
14 $crate::sync::Mutex::new( 14 $crate::sync::Mutex::new(
15 $inner, $crate::optional_name!($($ 15 $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
16 }; 16 };
17 } 17 }
18 pub use new_mutex; 18 pub use new_mutex;
19 19
20 /// A mutual exclusion primitive. 20 /// A mutual exclusion primitive.
21 /// 21 ///
22 /// Exposes the kernel's [`struct mutex`]. Whe 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, 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 wi 24 /// unlocked, at which point another thread will be allowed to wake up and make progress.
25 /// 25 ///
26 /// Since it may block, [`Mutex`] needs to be 26 /// Since it may block, [`Mutex`] needs to be used with care in atomic contexts.
27 /// 27 ///
28 /// Instances of [`Mutex`] need a lock class a 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:: 29 /// instances is with the [`pin_init`](crate::pin_init) and [`new_mutex`] macros.
30 /// 30 ///
31 /// # Examples 31 /// # Examples
32 /// 32 ///
33 /// The following example shows how to declare 33 /// The following example shows how to declare, allocate and initialise a struct (`Example`) that
34 /// contains an inner struct (`Inner`) that is 34 /// contains an inner struct (`Inner`) that is protected by a mutex.
35 /// 35 ///
36 /// ``` 36 /// ```
37 /// use kernel::sync::{new_mutex, Mutex}; 37 /// use kernel::sync::{new_mutex, Mutex};
38 /// 38 ///
39 /// struct Inner { 39 /// struct Inner {
40 /// a: u32, 40 /// a: u32,
41 /// b: u32, 41 /// b: u32,
42 /// } 42 /// }
43 /// 43 ///
44 /// #[pin_data] 44 /// #[pin_data]
45 /// struct Example { 45 /// struct Example {
46 /// c: u32, 46 /// c: u32,
47 /// #[pin] 47 /// #[pin]
48 /// d: Mutex<Inner>, 48 /// d: Mutex<Inner>,
49 /// } 49 /// }
50 /// 50 ///
51 /// impl Example { 51 /// impl Example {
52 /// fn new() -> impl PinInit<Self> { 52 /// fn new() -> impl PinInit<Self> {
53 /// pin_init!(Self { 53 /// pin_init!(Self {
54 /// c: 10, 54 /// c: 10,
55 /// d <- new_mutex!(Inner { a: 20, 55 /// d <- new_mutex!(Inner { a: 20, b: 30 }),
56 /// }) 56 /// })
57 /// } 57 /// }
58 /// } 58 /// }
59 /// 59 ///
60 /// // Allocate a boxed `Example`. 60 /// // Allocate a boxed `Example`.
61 /// let e = Box::pin_init(Example::new(), GFP_ 61 /// let e = Box::pin_init(Example::new(), GFP_KERNEL)?;
62 /// assert_eq!(e.c, 10); 62 /// assert_eq!(e.c, 10);
63 /// assert_eq!(e.d.lock().a, 20); 63 /// assert_eq!(e.d.lock().a, 20);
64 /// assert_eq!(e.d.lock().b, 30); 64 /// assert_eq!(e.d.lock().b, 30);
65 /// # Ok::<(), Error>(()) 65 /// # Ok::<(), Error>(())
66 /// ``` 66 /// ```
67 /// 67 ///
68 /// The following example shows how to use int 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 69 /// protected by a mutex despite only having a shared reference:
70 /// 70 ///
71 /// ``` 71 /// ```
72 /// use kernel::sync::Mutex; 72 /// use kernel::sync::Mutex;
73 /// 73 ///
74 /// struct Example { 74 /// struct Example {
75 /// a: u32, 75 /// a: u32,
76 /// b: u32, 76 /// b: u32,
77 /// } 77 /// }
78 /// 78 ///
79 /// fn example(m: &Mutex<Example>) { 79 /// fn example(m: &Mutex<Example>) {
80 /// let mut guard = m.lock(); 80 /// let mut guard = m.lock();
81 /// guard.a += 10; 81 /// guard.a += 10;
82 /// guard.b += 20; 82 /// guard.b += 20;
83 /// } 83 /// }
84 /// ``` 84 /// ```
85 /// 85 ///
86 /// [`struct mutex`]: srctree/include/linux/mu 86 /// [`struct mutex`]: srctree/include/linux/mutex.h
87 pub type Mutex<T> = super::Lock<T, MutexBacken 87 pub type Mutex<T> = super::Lock<T, MutexBackend>;
88 88
89 /// A kernel `struct mutex` lock backend. 89 /// A kernel `struct mutex` lock backend.
90 pub struct MutexBackend; 90 pub struct MutexBackend;
91 91
92 // SAFETY: The underlying kernel `struct mutex 92 // SAFETY: The underlying kernel `struct mutex` object ensures mutual exclusion.
93 unsafe impl super::Backend for MutexBackend { 93 unsafe impl super::Backend for MutexBackend {
94 type State = bindings::mutex; 94 type State = bindings::mutex;
95 type GuardState = (); 95 type GuardState = ();
96 96
97 unsafe fn init( 97 unsafe fn init(
98 ptr: *mut Self::State, 98 ptr: *mut Self::State,
99 name: *const core::ffi::c_char, 99 name: *const core::ffi::c_char,
100 key: *mut bindings::lock_class_key, 100 key: *mut bindings::lock_class_key,
101 ) { 101 ) {
102 // SAFETY: The safety requirements ens 102 // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
103 // `key` are valid for read indefinite 103 // `key` are valid for read indefinitely.
104 unsafe { bindings::__mutex_init(ptr, n 104 unsafe { bindings::__mutex_init(ptr, name, key) }
105 } 105 }
106 106
107 unsafe fn lock(ptr: *mut Self::State) -> S 107 unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
108 // SAFETY: The safety requirements of 108 // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
109 // memory, and that it has been initia 109 // memory, and that it has been initialised before.
110 unsafe { bindings::mutex_lock(ptr) }; 110 unsafe { bindings::mutex_lock(ptr) };
111 } 111 }
112 112
113 unsafe fn unlock(ptr: *mut Self::State, _g 113 unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
114 // SAFETY: The safety requirements of 114 // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
115 // caller is the owner of the mutex. 115 // caller is the owner of the mutex.
116 unsafe { bindings::mutex_unlock(ptr) } 116 unsafe { bindings::mutex_unlock(ptr) };
117 } 117 }
118 } 118 }
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