1 // SPDX-License-Identifier: GPL-2.0 1 // SPDX-License-Identifier: GPL-2.0
2 2
3 //! A reference-counted pointer. 3 //! A reference-counted pointer.
4 //! 4 //!
5 //! This module implements a way for users to 5 //! This module implements a way for users to create reference-counted objects and pointers to
6 //! them. Such a pointer automatically increme 6 //! them. Such a pointer automatically increments and decrements the count, and drops the
7 //! underlying object when it reaches zero. It 7 //! underlying object when it reaches zero. It is also safe to use concurrently from multiple
8 //! threads. 8 //! threads.
9 //! 9 //!
10 //! It is different from the standard library' 10 //! It is different from the standard library's [`Arc`] in a few ways:
11 //! 1. It is backed by the kernel's `refcount_ 11 //! 1. It is backed by the kernel's `refcount_t` type.
12 //! 2. It does not support weak references, wh 12 //! 2. It does not support weak references, which allows it to be half the size.
13 //! 3. It saturates the reference count instea 13 //! 3. It saturates the reference count instead of aborting when it goes over a threshold.
14 //! 4. It does not provide a `get_mut` method, 14 //! 4. It does not provide a `get_mut` method, so the ref counted object is pinned.
15 //! 5. The object in [`Arc`] is pinned implici <<
16 //! 15 //!
17 //! [`Arc`]: https://doc.rust-lang.org/std/syn 16 //! [`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
18 17
19 use crate::{ 18 use crate::{
20 alloc::{box_ext::BoxExt, AllocError, Flags <<
21 bindings, 19 bindings,
22 init::{self, InPlaceInit, Init, PinInit}, !! 20 error::Result,
23 try_init, <<
24 types::{ForeignOwnable, Opaque}, 21 types::{ForeignOwnable, Opaque},
25 }; 22 };
26 use alloc::boxed::Box; 23 use alloc::boxed::Box;
27 use core::{ 24 use core::{
28 alloc::Layout, <<
29 fmt, <<
30 marker::{PhantomData, Unsize}, 25 marker::{PhantomData, Unsize},
31 mem::{ManuallyDrop, MaybeUninit}, 26 mem::{ManuallyDrop, MaybeUninit},
32 ops::{Deref, DerefMut}, 27 ops::{Deref, DerefMut},
33 pin::Pin, 28 pin::Pin,
34 ptr::NonNull, 29 ptr::NonNull,
35 }; 30 };
36 use macros::pin_data; <<
37 <<
38 mod std_vendor; <<
39 31
40 /// A reference-counted pointer to an instance 32 /// A reference-counted pointer to an instance of `T`.
41 /// 33 ///
42 /// The reference count is incremented when ne 34 /// The reference count is incremented when new instances of [`Arc`] are created, and decremented
43 /// when they are dropped. When the count reac 35 /// when they are dropped. When the count reaches zero, the underlying `T` is also dropped.
44 /// 36 ///
45 /// # Invariants 37 /// # Invariants
46 /// 38 ///
47 /// The reference count on an instance of [`Ar 39 /// The reference count on an instance of [`Arc`] is always non-zero.
48 /// The object pointed to by [`Arc`] is always 40 /// The object pointed to by [`Arc`] is always pinned.
49 /// 41 ///
50 /// # Examples 42 /// # Examples
51 /// 43 ///
52 /// ``` 44 /// ```
53 /// use kernel::sync::Arc; 45 /// use kernel::sync::Arc;
54 /// 46 ///
55 /// struct Example { 47 /// struct Example {
56 /// a: u32, 48 /// a: u32,
57 /// b: u32, 49 /// b: u32,
58 /// } 50 /// }
59 /// 51 ///
60 /// // Create a refcounted instance of `Exampl !! 52 /// // Create a ref-counted instance of `Example`.
61 /// let obj = Arc::new(Example { a: 10, b: 20 !! 53 /// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
62 /// 54 ///
63 /// // Get a new pointer to `obj` and incremen 55 /// // Get a new pointer to `obj` and increment the refcount.
64 /// let cloned = obj.clone(); 56 /// let cloned = obj.clone();
65 /// 57 ///
66 /// // Assert that both `obj` and `cloned` poi 58 /// // Assert that both `obj` and `cloned` point to the same underlying object.
67 /// assert!(core::ptr::eq(&*obj, &*cloned)); 59 /// assert!(core::ptr::eq(&*obj, &*cloned));
68 /// 60 ///
69 /// // Destroy `obj` and decrement its refcoun 61 /// // Destroy `obj` and decrement its refcount.
70 /// drop(obj); 62 /// drop(obj);
71 /// 63 ///
72 /// // Check that the values are still accessi 64 /// // Check that the values are still accessible through `cloned`.
73 /// assert_eq!(cloned.a, 10); 65 /// assert_eq!(cloned.a, 10);
74 /// assert_eq!(cloned.b, 20); 66 /// assert_eq!(cloned.b, 20);
75 /// 67 ///
76 /// // The refcount drops to zero when `cloned 68 /// // The refcount drops to zero when `cloned` goes out of scope, and the memory is freed.
77 /// # Ok::<(), Error>(()) <<
78 /// ``` 69 /// ```
79 /// 70 ///
80 /// Using `Arc<T>` as the type of `self`: 71 /// Using `Arc<T>` as the type of `self`:
81 /// 72 ///
82 /// ``` 73 /// ```
83 /// use kernel::sync::Arc; 74 /// use kernel::sync::Arc;
84 /// 75 ///
85 /// struct Example { 76 /// struct Example {
86 /// a: u32, 77 /// a: u32,
87 /// b: u32, 78 /// b: u32,
88 /// } 79 /// }
89 /// 80 ///
90 /// impl Example { 81 /// impl Example {
91 /// fn take_over(self: Arc<Self>) { 82 /// fn take_over(self: Arc<Self>) {
92 /// // ... 83 /// // ...
93 /// } 84 /// }
94 /// 85 ///
95 /// fn use_reference(self: &Arc<Self>) { 86 /// fn use_reference(self: &Arc<Self>) {
96 /// // ... 87 /// // ...
97 /// } 88 /// }
98 /// } 89 /// }
99 /// 90 ///
100 /// let obj = Arc::new(Example { a: 10, b: 20 !! 91 /// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
101 /// obj.use_reference(); 92 /// obj.use_reference();
102 /// obj.take_over(); 93 /// obj.take_over();
103 /// # Ok::<(), Error>(()) <<
104 /// ``` 94 /// ```
105 /// 95 ///
106 /// Coercion from `Arc<Example>` to `Arc<dyn M 96 /// Coercion from `Arc<Example>` to `Arc<dyn MyTrait>`:
107 /// 97 ///
108 /// ``` 98 /// ```
109 /// use kernel::sync::{Arc, ArcBorrow}; 99 /// use kernel::sync::{Arc, ArcBorrow};
110 /// 100 ///
111 /// trait MyTrait { 101 /// trait MyTrait {
112 /// // Trait has a function whose `self` t 102 /// // Trait has a function whose `self` type is `Arc<Self>`.
113 /// fn example1(self: Arc<Self>) {} 103 /// fn example1(self: Arc<Self>) {}
114 /// 104 ///
115 /// // Trait has a function whose `self` t 105 /// // Trait has a function whose `self` type is `ArcBorrow<'_, Self>`.
116 /// fn example2(self: ArcBorrow<'_, Self>) 106 /// fn example2(self: ArcBorrow<'_, Self>) {}
117 /// } 107 /// }
118 /// 108 ///
119 /// struct Example; 109 /// struct Example;
120 /// impl MyTrait for Example {} 110 /// impl MyTrait for Example {}
121 /// 111 ///
122 /// // `obj` has type `Arc<Example>`. 112 /// // `obj` has type `Arc<Example>`.
123 /// let obj: Arc<Example> = Arc::new(Example, !! 113 /// let obj: Arc<Example> = Arc::try_new(Example)?;
124 /// 114 ///
125 /// // `coerced` has type `Arc<dyn MyTrait>`. 115 /// // `coerced` has type `Arc<dyn MyTrait>`.
126 /// let coerced: Arc<dyn MyTrait> = obj; 116 /// let coerced: Arc<dyn MyTrait> = obj;
127 /// # Ok::<(), Error>(()) <<
128 /// ``` 117 /// ```
129 pub struct Arc<T: ?Sized> { 118 pub struct Arc<T: ?Sized> {
130 ptr: NonNull<ArcInner<T>>, 119 ptr: NonNull<ArcInner<T>>,
131 _p: PhantomData<ArcInner<T>>, 120 _p: PhantomData<ArcInner<T>>,
132 } 121 }
133 122
134 #[pin_data] <<
135 #[repr(C)] 123 #[repr(C)]
136 struct ArcInner<T: ?Sized> { 124 struct ArcInner<T: ?Sized> {
137 refcount: Opaque<bindings::refcount_t>, 125 refcount: Opaque<bindings::refcount_t>,
138 data: T, 126 data: T,
139 } 127 }
140 128
141 impl<T: ?Sized> ArcInner<T> { <<
142 /// Converts a pointer to the contents of <<
143 /// <<
144 /// # Safety <<
145 /// <<
146 /// `ptr` must have been returned by a pre <<
147 /// not yet have been destroyed. <<
148 unsafe fn container_of(ptr: *const T) -> N <<
149 let refcount_layout = Layout::new::<bi <<
150 // SAFETY: The caller guarantees that <<
151 let val_layout = Layout::for_value(uns <<
152 // SAFETY: We're computing the layout <<
153 // binary, so its layout is not so lar <<
154 let val_offset = unsafe { refcount_lay <<
155 <<
156 // Pointer casts leave the metadata un <<
157 // `ArcInner<T>` is the same since `Ar <<
158 // <<
159 // This is documented at: <<
160 // <https://doc.rust-lang.org/std/ptr/ <<
161 let ptr = ptr as *const ArcInner<T>; <<
162 <<
163 // SAFETY: The pointer is in-bounds of <<
164 // pointer, since it originates from a <<
165 // still valid. <<
166 let ptr = unsafe { ptr.byte_sub(val_of <<
167 <<
168 // SAFETY: The pointer can't be null s <<
169 // address. <<
170 unsafe { NonNull::new_unchecked(ptr.ca <<
171 } <<
172 } <<
173 <<
174 // This is to allow [`Arc`] (and variants) to 129 // This is to allow [`Arc`] (and variants) to be used as the type of `self`.
175 impl<T: ?Sized> core::ops::Receiver for Arc<T> 130 impl<T: ?Sized> core::ops::Receiver for Arc<T> {}
176 131
177 // This is to allow coercion from `Arc<T>` to 132 // This is to allow coercion from `Arc<T>` to `Arc<U>` if `T` can be converted to the
178 // dynamically-sized type (DST) `U`. 133 // dynamically-sized type (DST) `U`.
179 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::o 134 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::CoerceUnsized<Arc<U>> for Arc<T> {}
180 135
181 // This is to allow `Arc<U>` to be dispatched 136 // This is to allow `Arc<U>` to be dispatched on when `Arc<T>` can be coerced into `Arc<U>`.
182 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::o 137 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<Arc<U>> for Arc<T> {}
183 138
184 // SAFETY: It is safe to send `Arc<T>` to anot 139 // SAFETY: It is safe to send `Arc<T>` to another thread when the underlying `T` is `Sync` because
185 // it effectively means sharing `&T` (which is 140 // it effectively means sharing `&T` (which is safe because `T` is `Sync`); additionally, it needs
186 // `T` to be `Send` because any thread that ha !! 141 // `T` to be `Send` because any thread that has an `Arc<T>` may ultimately access `T` directly, for
187 // mutable reference when the reference count !! 142 // example, when the reference count reaches zero and `T` is dropped.
188 unsafe impl<T: ?Sized + Sync + Send> Send for 143 unsafe impl<T: ?Sized + Sync + Send> Send for Arc<T> {}
189 144
190 // SAFETY: It is safe to send `&Arc<T>` to ano !! 145 // SAFETY: It is safe to send `&Arc<T>` to another thread when the underlying `T` is `Sync` for the
191 // because it effectively means sharing `&T` ( !! 146 // same reason as above. `T` needs to be `Send` as well because a thread can clone an `&Arc<T>`
192 // it needs `T` to be `Send` because any threa !! 147 // into an `Arc<T>`, which may lead to `T` being accessed by the same reasoning as above.
193 // `Arc<T>` on that thread, so the thread may <<
194 // the reference count reaches zero and `T` is <<
195 unsafe impl<T: ?Sized + Sync + Send> Sync for 148 unsafe impl<T: ?Sized + Sync + Send> Sync for Arc<T> {}
196 149
197 impl<T> Arc<T> { 150 impl<T> Arc<T> {
198 /// Constructs a new reference counted ins 151 /// Constructs a new reference counted instance of `T`.
199 pub fn new(contents: T, flags: Flags) -> R !! 152 pub fn try_new(contents: T) -> Result<Self> {
200 // INVARIANT: The refcount is initiali 153 // INVARIANT: The refcount is initialised to a non-zero value.
201 let value = ArcInner { 154 let value = ArcInner {
202 // SAFETY: There are no safety req 155 // SAFETY: There are no safety requirements for this FFI call.
203 refcount: Opaque::new(unsafe { bin 156 refcount: Opaque::new(unsafe { bindings::REFCOUNT_INIT(1) }),
204 data: contents, 157 data: contents,
205 }; 158 };
206 159
207 let inner = <Box<_> as BoxExt<_>>::new !! 160 let inner = Box::try_new(value)?;
208 161
209 // SAFETY: We just created `inner` wit 162 // SAFETY: We just created `inner` with a reference count of 1, which is owned by the new
210 // `Arc` object. 163 // `Arc` object.
211 Ok(unsafe { Self::from_inner(Box::leak 164 Ok(unsafe { Self::from_inner(Box::leak(inner).into()) })
212 } 165 }
213 } 166 }
214 167
215 impl<T: ?Sized> Arc<T> { 168 impl<T: ?Sized> Arc<T> {
216 /// Constructs a new [`Arc`] from an exist 169 /// Constructs a new [`Arc`] from an existing [`ArcInner`].
217 /// 170 ///
218 /// # Safety 171 /// # Safety
219 /// 172 ///
220 /// The caller must ensure that `inner` po 173 /// The caller must ensure that `inner` points to a valid location and has a non-zero reference
221 /// count, one of which will be owned by t 174 /// count, one of which will be owned by the new [`Arc`] instance.
222 unsafe fn from_inner(inner: NonNull<ArcInn 175 unsafe fn from_inner(inner: NonNull<ArcInner<T>>) -> Self {
223 // INVARIANT: By the safety requiremen 176 // INVARIANT: By the safety requirements, the invariants hold.
224 Arc { 177 Arc {
225 ptr: inner, 178 ptr: inner,
226 _p: PhantomData, 179 _p: PhantomData,
227 } 180 }
228 } 181 }
229 182
230 /// Convert the [`Arc`] into a raw pointer <<
231 /// <<
232 /// The raw pointer has ownership of the r <<
233 pub fn into_raw(self) -> *const T { <<
234 let ptr = self.ptr.as_ptr(); <<
235 core::mem::forget(self); <<
236 // SAFETY: The pointer is valid. <<
237 unsafe { core::ptr::addr_of!((*ptr).da <<
238 } <<
239 <<
240 /// Recreates an [`Arc`] instance previous <<
241 /// <<
242 /// # Safety <<
243 /// <<
244 /// `ptr` must have been returned by a pre <<
245 /// must not be called more than once for <<
246 pub unsafe fn from_raw(ptr: *const T) -> S <<
247 // SAFETY: The caller promises that th <<
248 // `Arc` that is still valid. <<
249 let ptr = unsafe { ArcInner::container <<
250 <<
251 // SAFETY: By the safety requirements <<
252 // reference count held then will be o <<
253 unsafe { Self::from_inner(ptr) } <<
254 } <<
255 <<
256 /// Returns an [`ArcBorrow`] from the give 183 /// Returns an [`ArcBorrow`] from the given [`Arc`].
257 /// 184 ///
258 /// This is useful when the argument of a 185 /// This is useful when the argument of a function call is an [`ArcBorrow`] (e.g., in a method
259 /// receiver), but we have an [`Arc`] inst 186 /// receiver), but we have an [`Arc`] instead. Getting an [`ArcBorrow`] is free when optimised.
260 #[inline] 187 #[inline]
261 pub fn as_arc_borrow(&self) -> ArcBorrow<' 188 pub fn as_arc_borrow(&self) -> ArcBorrow<'_, T> {
262 // SAFETY: The constraint that the lif 189 // SAFETY: The constraint that the lifetime of the shared reference must outlive that of
263 // the returned `ArcBorrow` ensures th 190 // the returned `ArcBorrow` ensures that the object remains alive and that no mutable
264 // reference can be created. 191 // reference can be created.
265 unsafe { ArcBorrow::new(self.ptr) } 192 unsafe { ArcBorrow::new(self.ptr) }
266 } 193 }
267 <<
268 /// Compare whether two [`Arc`] pointers r <<
269 pub fn ptr_eq(this: &Self, other: &Self) - <<
270 core::ptr::eq(this.ptr.as_ptr(), other <<
271 } <<
272 <<
273 /// Converts this [`Arc`] into a [`UniqueA <<
274 /// <<
275 /// When this destroys the `Arc`, it does <<
276 /// this method will never call the destru <<
277 /// <<
278 /// # Examples <<
279 /// <<
280 /// ``` <<
281 /// use kernel::sync::{Arc, UniqueArc}; <<
282 /// <<
283 /// let arc = Arc::new(42, GFP_KERNEL)?; <<
284 /// let unique_arc = arc.into_unique_or_dr <<
285 /// <<
286 /// // The above conversion should succeed <<
287 /// assert!(unique_arc.is_some()); <<
288 /// <<
289 /// assert_eq!(*(unique_arc.unwrap()), 42) <<
290 /// <<
291 /// # Ok::<(), Error>(()) <<
292 /// ``` <<
293 /// <<
294 /// ``` <<
295 /// use kernel::sync::{Arc, UniqueArc}; <<
296 /// <<
297 /// let arc = Arc::new(42, GFP_KERNEL)?; <<
298 /// let another = arc.clone(); <<
299 /// <<
300 /// let unique_arc = arc.into_unique_or_dr <<
301 /// <<
302 /// // The above conversion should fail si <<
303 /// assert!(unique_arc.is_none()); <<
304 /// <<
305 /// # Ok::<(), Error>(()) <<
306 /// ``` <<
307 pub fn into_unique_or_drop(self) -> Option <<
308 // We will manually manage the refcoun <<
309 let me = ManuallyDrop::new(self); <<
310 // SAFETY: We own a refcount, so the p <<
311 let refcount = unsafe { me.ptr.as_ref( <<
312 <<
313 // If the refcount reaches a non-zero <<
314 // return without further touching the <<
315 // no other arcs, and we can create a <<
316 // <<
317 // SAFETY: We own a refcount, so the p <<
318 let is_zero = unsafe { bindings::refco <<
319 if is_zero { <<
320 // SAFETY: We have exclusive acces <<
321 // accesses to the refcount. <<
322 unsafe { core::ptr::write(refcount <<
323 <<
324 // INVARIANT: We own the only refc <<
325 // must pin the `UniqueArc` becaus <<
326 // their values. <<
327 Some(Pin::from(UniqueArc { <<
328 inner: ManuallyDrop::into_inne <<
329 })) <<
330 } else { <<
331 None <<
332 } <<
333 } <<
334 } 194 }
335 195
336 impl<T: 'static> ForeignOwnable for Arc<T> { 196 impl<T: 'static> ForeignOwnable for Arc<T> {
337 type Borrowed<'a> = ArcBorrow<'a, T>; 197 type Borrowed<'a> = ArcBorrow<'a, T>;
338 198
339 fn into_foreign(self) -> *const core::ffi: 199 fn into_foreign(self) -> *const core::ffi::c_void {
340 ManuallyDrop::new(self).ptr.as_ptr() a 200 ManuallyDrop::new(self).ptr.as_ptr() as _
341 } 201 }
342 202
343 unsafe fn borrow<'a>(ptr: *const core::ffi 203 unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
344 // SAFETY: By the safety requirement o 204 // SAFETY: By the safety requirement of this function, we know that `ptr` came from
345 // a previous call to `Arc::into_forei 205 // a previous call to `Arc::into_foreign`.
346 let inner = NonNull::new(ptr as *mut A 206 let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
347 207
348 // SAFETY: The safety requirements of 208 // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
349 // for the lifetime of the returned va !! 209 // for the lifetime of the returned value. Additionally, the safety requirements of
>> 210 // `ForeignOwnable::borrow_mut` ensure that no new mutable references are created.
350 unsafe { ArcBorrow::new(inner) } 211 unsafe { ArcBorrow::new(inner) }
351 } 212 }
352 213
353 unsafe fn from_foreign(ptr: *const core::f 214 unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self {
354 // SAFETY: By the safety requirement o 215 // SAFETY: By the safety requirement of this function, we know that `ptr` came from
355 // a previous call to `Arc::into_forei 216 // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
356 // holds a reference count increment t 217 // holds a reference count increment that is transferrable to us.
357 unsafe { Self::from_inner(NonNull::new 218 unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
358 } 219 }
359 } 220 }
360 221
361 impl<T: ?Sized> Deref for Arc<T> { 222 impl<T: ?Sized> Deref for Arc<T> {
362 type Target = T; 223 type Target = T;
363 224
364 fn deref(&self) -> &Self::Target { 225 fn deref(&self) -> &Self::Target {
365 // SAFETY: By the type invariant, ther 226 // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
366 // safe to dereference it. 227 // safe to dereference it.
367 unsafe { &self.ptr.as_ref().data } 228 unsafe { &self.ptr.as_ref().data }
368 } 229 }
369 } 230 }
370 231
371 impl<T: ?Sized> AsRef<T> for Arc<T> { <<
372 fn as_ref(&self) -> &T { <<
373 self.deref() <<
374 } <<
375 } <<
376 <<
377 impl<T: ?Sized> Clone for Arc<T> { 232 impl<T: ?Sized> Clone for Arc<T> {
378 fn clone(&self) -> Self { 233 fn clone(&self) -> Self {
379 // INVARIANT: C `refcount_inc` saturat 234 // INVARIANT: C `refcount_inc` saturates the refcount, so it cannot overflow to zero.
380 // SAFETY: By the type invariant, ther 235 // SAFETY: By the type invariant, there is necessarily a reference to the object, so it is
381 // safe to increment the refcount. 236 // safe to increment the refcount.
382 unsafe { bindings::refcount_inc(self.p 237 unsafe { bindings::refcount_inc(self.ptr.as_ref().refcount.get()) };
383 238
384 // SAFETY: We just incremented the ref 239 // SAFETY: We just incremented the refcount. This increment is now owned by the new `Arc`.
385 unsafe { Self::from_inner(self.ptr) } 240 unsafe { Self::from_inner(self.ptr) }
386 } 241 }
387 } 242 }
388 243
389 impl<T: ?Sized> Drop for Arc<T> { 244 impl<T: ?Sized> Drop for Arc<T> {
390 fn drop(&mut self) { 245 fn drop(&mut self) {
391 // SAFETY: By the type invariant, ther 246 // SAFETY: By the type invariant, there is necessarily a reference to the object. We cannot
392 // touch `refcount` after it's decreme 247 // touch `refcount` after it's decremented to a non-zero value because another thread/CPU
393 // may concurrently decrement it to ze 248 // may concurrently decrement it to zero and free it. It is ok to have a raw pointer to
394 // freed/invalid memory as long as it 249 // freed/invalid memory as long as it is never dereferenced.
395 let refcount = unsafe { self.ptr.as_re 250 let refcount = unsafe { self.ptr.as_ref() }.refcount.get();
396 251
397 // INVARIANT: If the refcount reaches 252 // INVARIANT: If the refcount reaches zero, there are no other instances of `Arc`, and
398 // this instance is being dropped, so 253 // this instance is being dropped, so the broken invariant is not observable.
399 // SAFETY: Also by the type invariant, 254 // SAFETY: Also by the type invariant, we are allowed to decrement the refcount.
400 let is_zero = unsafe { bindings::refco 255 let is_zero = unsafe { bindings::refcount_dec_and_test(refcount) };
401 if is_zero { 256 if is_zero {
402 // The count reached zero, we must 257 // The count reached zero, we must free the memory.
403 // 258 //
404 // SAFETY: The pointer was initial 259 // SAFETY: The pointer was initialised from the result of `Box::leak`.
405 unsafe { drop(Box::from_raw(self.p !! 260 unsafe { Box::from_raw(self.ptr.as_ptr()) };
406 } 261 }
407 } 262 }
408 } 263 }
409 264
410 impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> 265 impl<T: ?Sized> From<UniqueArc<T>> for Arc<T> {
411 fn from(item: UniqueArc<T>) -> Self { 266 fn from(item: UniqueArc<T>) -> Self {
412 item.inner 267 item.inner
413 } 268 }
414 } 269 }
415 270
416 impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Ar 271 impl<T: ?Sized> From<Pin<UniqueArc<T>>> for Arc<T> {
417 fn from(item: Pin<UniqueArc<T>>) -> Self { 272 fn from(item: Pin<UniqueArc<T>>) -> Self {
418 // SAFETY: The type invariants of `Arc 273 // SAFETY: The type invariants of `Arc` guarantee that the data is pinned.
419 unsafe { Pin::into_inner_unchecked(ite 274 unsafe { Pin::into_inner_unchecked(item).inner }
420 } 275 }
421 } 276 }
422 277
423 /// A borrowed reference to an [`Arc`] instanc 278 /// A borrowed reference to an [`Arc`] instance.
424 /// 279 ///
425 /// For cases when one doesn't ever need to in 280 /// For cases when one doesn't ever need to increment the refcount on the allocation, it is simpler
426 /// to use just `&T`, which we can trivially g !! 281 /// to use just `&T`, which we can trivially get from an `Arc<T>` instance.
427 /// 282 ///
428 /// However, when one may need to increment th 283 /// However, when one may need to increment the refcount, it is preferable to use an `ArcBorrow<T>`
429 /// over `&Arc<T>` because the latter results 284 /// over `&Arc<T>` because the latter results in a double-indirection: a pointer (shared reference)
430 /// to a pointer ([`Arc<T>`]) to the object (` !! 285 /// to a pointer (`Arc<T>`) to the object (`T`). An [`ArcBorrow`] eliminates this double
431 /// indirection while still allowing one to in !! 286 /// indirection while still allowing one to increment the refcount and getting an `Arc<T>` when/if
432 /// needed. 287 /// needed.
433 /// 288 ///
434 /// # Invariants 289 /// # Invariants
435 /// 290 ///
436 /// There are no mutable references to the und 291 /// There are no mutable references to the underlying [`Arc`], and it remains valid for the
437 /// lifetime of the [`ArcBorrow`] instance. 292 /// lifetime of the [`ArcBorrow`] instance.
438 /// 293 ///
439 /// # Example 294 /// # Example
440 /// 295 ///
441 /// ``` 296 /// ```
442 /// use kernel::sync::{Arc, ArcBorrow}; !! 297 /// use crate::sync::{Arc, ArcBorrow};
443 /// 298 ///
444 /// struct Example; 299 /// struct Example;
445 /// 300 ///
446 /// fn do_something(e: ArcBorrow<'_, Example>) 301 /// fn do_something(e: ArcBorrow<'_, Example>) -> Arc<Example> {
447 /// e.into() 302 /// e.into()
448 /// } 303 /// }
449 /// 304 ///
450 /// let obj = Arc::new(Example, GFP_KERNEL)?; !! 305 /// let obj = Arc::try_new(Example)?;
451 /// let cloned = do_something(obj.as_arc_borro 306 /// let cloned = do_something(obj.as_arc_borrow());
452 /// 307 ///
453 /// // Assert that both `obj` and `cloned` poi 308 /// // Assert that both `obj` and `cloned` point to the same underlying object.
454 /// assert!(core::ptr::eq(&*obj, &*cloned)); 309 /// assert!(core::ptr::eq(&*obj, &*cloned));
455 /// # Ok::<(), Error>(()) <<
456 /// ``` 310 /// ```
457 /// 311 ///
458 /// Using `ArcBorrow<T>` as the type of `self` 312 /// Using `ArcBorrow<T>` as the type of `self`:
459 /// 313 ///
460 /// ``` 314 /// ```
461 /// use kernel::sync::{Arc, ArcBorrow}; !! 315 /// use crate::sync::{Arc, ArcBorrow};
462 /// 316 ///
463 /// struct Example { 317 /// struct Example {
464 /// a: u32, 318 /// a: u32,
465 /// b: u32, 319 /// b: u32,
466 /// } 320 /// }
467 /// 321 ///
468 /// impl Example { 322 /// impl Example {
469 /// fn use_reference(self: ArcBorrow<'_, S 323 /// fn use_reference(self: ArcBorrow<'_, Self>) {
470 /// // ... 324 /// // ...
471 /// } 325 /// }
472 /// } 326 /// }
473 /// 327 ///
474 /// let obj = Arc::new(Example { a: 10, b: 20 !! 328 /// let obj = Arc::try_new(Example { a: 10, b: 20 })?;
475 /// obj.as_arc_borrow().use_reference(); 329 /// obj.as_arc_borrow().use_reference();
476 /// # Ok::<(), Error>(()) <<
477 /// ``` 330 /// ```
478 pub struct ArcBorrow<'a, T: ?Sized + 'a> { 331 pub struct ArcBorrow<'a, T: ?Sized + 'a> {
479 inner: NonNull<ArcInner<T>>, 332 inner: NonNull<ArcInner<T>>,
480 _p: PhantomData<&'a ()>, 333 _p: PhantomData<&'a ()>,
481 } 334 }
482 335
483 // This is to allow [`ArcBorrow`] (and variant 336 // This is to allow [`ArcBorrow`] (and variants) to be used as the type of `self`.
484 impl<T: ?Sized> core::ops::Receiver for ArcBor 337 impl<T: ?Sized> core::ops::Receiver for ArcBorrow<'_, T> {}
485 338
486 // This is to allow `ArcBorrow<U>` to be dispa 339 // This is to allow `ArcBorrow<U>` to be dispatched on when `ArcBorrow<T>` can be coerced into
487 // `ArcBorrow<U>`. 340 // `ArcBorrow<U>`.
488 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::o 341 impl<T: ?Sized + Unsize<U>, U: ?Sized> core::ops::DispatchFromDyn<ArcBorrow<'_, U>>
489 for ArcBorrow<'_, T> 342 for ArcBorrow<'_, T>
490 { 343 {
491 } 344 }
492 345
493 impl<T: ?Sized> Clone for ArcBorrow<'_, T> { 346 impl<T: ?Sized> Clone for ArcBorrow<'_, T> {
494 fn clone(&self) -> Self { 347 fn clone(&self) -> Self {
495 *self 348 *self
496 } 349 }
497 } 350 }
498 351
499 impl<T: ?Sized> Copy for ArcBorrow<'_, T> {} 352 impl<T: ?Sized> Copy for ArcBorrow<'_, T> {}
500 353
501 impl<T: ?Sized> ArcBorrow<'_, T> { 354 impl<T: ?Sized> ArcBorrow<'_, T> {
502 /// Creates a new [`ArcBorrow`] instance. 355 /// Creates a new [`ArcBorrow`] instance.
503 /// 356 ///
504 /// # Safety 357 /// # Safety
505 /// 358 ///
506 /// Callers must ensure the following for 359 /// Callers must ensure the following for the lifetime of the returned [`ArcBorrow`] instance:
507 /// 1. That `inner` remains valid; 360 /// 1. That `inner` remains valid;
508 /// 2. That no mutable references to `inne 361 /// 2. That no mutable references to `inner` are created.
509 unsafe fn new(inner: NonNull<ArcInner<T>>) 362 unsafe fn new(inner: NonNull<ArcInner<T>>) -> Self {
510 // INVARIANT: The safety requirements 363 // INVARIANT: The safety requirements guarantee the invariants.
511 Self { 364 Self {
512 inner, 365 inner,
513 _p: PhantomData, 366 _p: PhantomData,
514 } 367 }
515 } 368 }
516 <<
517 /// Creates an [`ArcBorrow`] to an [`Arc`] <<
518 /// [`Arc::into_raw`]. <<
519 /// <<
520 /// # Safety <<
521 /// <<
522 /// * The provided pointer must originate <<
523 /// * For the duration of the lifetime ann <<
524 /// not hit zero. <<
525 /// * For the duration of the lifetime ann <<
526 /// [`UniqueArc`] reference to this valu <<
527 pub unsafe fn from_raw(ptr: *const T) -> S <<
528 // SAFETY: The caller promises that th <<
529 // `Arc` that is still valid. <<
530 let ptr = unsafe { ArcInner::container <<
531 <<
532 // SAFETY: The caller promises that th <<
533 // not hit zero, and no mutable refere <<
534 // `UniqueArc`. <<
535 unsafe { Self::new(ptr) } <<
536 } <<
537 } 369 }
538 370
539 impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc 371 impl<T: ?Sized> From<ArcBorrow<'_, T>> for Arc<T> {
540 fn from(b: ArcBorrow<'_, T>) -> Self { 372 fn from(b: ArcBorrow<'_, T>) -> Self {
541 // SAFETY: The existence of `b` guaran 373 // SAFETY: The existence of `b` guarantees that the refcount is non-zero. `ManuallyDrop`
542 // guarantees that `drop` isn't called 374 // guarantees that `drop` isn't called, so it's ok that the temporary `Arc` doesn't own the
543 // increment. 375 // increment.
544 ManuallyDrop::new(unsafe { Arc::from_i 376 ManuallyDrop::new(unsafe { Arc::from_inner(b.inner) })
545 .deref() 377 .deref()
546 .clone() 378 .clone()
547 } 379 }
548 } 380 }
549 381
550 impl<T: ?Sized> Deref for ArcBorrow<'_, T> { 382 impl<T: ?Sized> Deref for ArcBorrow<'_, T> {
551 type Target = T; 383 type Target = T;
552 384
553 fn deref(&self) -> &Self::Target { 385 fn deref(&self) -> &Self::Target {
554 // SAFETY: By the type invariant, the 386 // SAFETY: By the type invariant, the underlying object is still alive with no mutable
555 // references to it, so it is safe to 387 // references to it, so it is safe to create a shared reference.
556 unsafe { &self.inner.as_ref().data } 388 unsafe { &self.inner.as_ref().data }
557 } 389 }
558 } 390 }
559 391
560 /// A refcounted object that is known to have 392 /// A refcounted object that is known to have a refcount of 1.
561 /// 393 ///
562 /// It is mutable and can be converted to an [ 394 /// It is mutable and can be converted to an [`Arc`] so that it can be shared.
563 /// 395 ///
564 /// # Invariants 396 /// # Invariants
565 /// 397 ///
566 /// `inner` always has a reference count of 1. 398 /// `inner` always has a reference count of 1.
567 /// 399 ///
568 /// # Examples 400 /// # Examples
569 /// 401 ///
570 /// In the following example, we make changes 402 /// In the following example, we make changes to the inner object before turning it into an
571 /// `Arc<Test>` object (after which point, it 403 /// `Arc<Test>` object (after which point, it cannot be mutated directly). Note that `x.into()`
572 /// cannot fail. 404 /// cannot fail.
573 /// 405 ///
574 /// ``` 406 /// ```
575 /// use kernel::sync::{Arc, UniqueArc}; 407 /// use kernel::sync::{Arc, UniqueArc};
576 /// 408 ///
577 /// struct Example { 409 /// struct Example {
578 /// a: u32, 410 /// a: u32,
579 /// b: u32, 411 /// b: u32,
580 /// } 412 /// }
581 /// 413 ///
582 /// fn test() -> Result<Arc<Example>> { 414 /// fn test() -> Result<Arc<Example>> {
583 /// let mut x = UniqueArc::new(Example { a !! 415 /// let mut x = UniqueArc::try_new(Example { a: 10, b: 20 })?;
584 /// x.a += 1; 416 /// x.a += 1;
585 /// x.b += 1; 417 /// x.b += 1;
586 /// Ok(x.into()) 418 /// Ok(x.into())
587 /// } 419 /// }
588 /// 420 ///
589 /// # test().unwrap(); 421 /// # test().unwrap();
590 /// ``` 422 /// ```
591 /// 423 ///
592 /// In the following example we first allocate !! 424 /// In the following example we first allocate memory for a ref-counted `Example` but we don't
593 /// initialise it on allocation. We do initial 425 /// initialise it on allocation. We do initialise it later with a call to [`UniqueArc::write`],
594 /// followed by a conversion to `Arc<Example>` 426 /// followed by a conversion to `Arc<Example>`. This is particularly useful when allocation happens
595 /// in one context (e.g., sleepable) and initi 427 /// in one context (e.g., sleepable) and initialisation in another (e.g., atomic):
596 /// 428 ///
597 /// ``` 429 /// ```
598 /// use kernel::sync::{Arc, UniqueArc}; 430 /// use kernel::sync::{Arc, UniqueArc};
599 /// 431 ///
600 /// struct Example { 432 /// struct Example {
601 /// a: u32, 433 /// a: u32,
602 /// b: u32, 434 /// b: u32,
603 /// } 435 /// }
604 /// 436 ///
605 /// fn test() -> Result<Arc<Example>> { 437 /// fn test() -> Result<Arc<Example>> {
606 /// let x = UniqueArc::new_uninit(GFP_KERN !! 438 /// let x = UniqueArc::try_new_uninit()?;
607 /// Ok(x.write(Example { a: 10, b: 20 }).i 439 /// Ok(x.write(Example { a: 10, b: 20 }).into())
608 /// } 440 /// }
609 /// 441 ///
610 /// # test().unwrap(); 442 /// # test().unwrap();
611 /// ``` 443 /// ```
612 /// 444 ///
613 /// In the last example below, the caller gets 445 /// In the last example below, the caller gets a pinned instance of `Example` while converting to
614 /// `Arc<Example>`; this is useful in scenario 446 /// `Arc<Example>`; this is useful in scenarios where one needs a pinned reference during
615 /// initialisation, for example, when initiali 447 /// initialisation, for example, when initialising fields that are wrapped in locks.
616 /// 448 ///
617 /// ``` 449 /// ```
618 /// use kernel::sync::{Arc, UniqueArc}; 450 /// use kernel::sync::{Arc, UniqueArc};
619 /// 451 ///
620 /// struct Example { 452 /// struct Example {
621 /// a: u32, 453 /// a: u32,
622 /// b: u32, 454 /// b: u32,
623 /// } 455 /// }
624 /// 456 ///
625 /// fn test() -> Result<Arc<Example>> { 457 /// fn test() -> Result<Arc<Example>> {
626 /// let mut pinned = Pin::from(UniqueArc:: !! 458 /// let mut pinned = Pin::from(UniqueArc::try_new(Example { a: 10, b: 20 })?);
627 /// // We can modify `pinned` because it i 459 /// // We can modify `pinned` because it is `Unpin`.
628 /// pinned.as_mut().a += 1; 460 /// pinned.as_mut().a += 1;
629 /// Ok(pinned.into()) 461 /// Ok(pinned.into())
630 /// } 462 /// }
631 /// 463 ///
632 /// # test().unwrap(); 464 /// # test().unwrap();
633 /// ``` 465 /// ```
634 pub struct UniqueArc<T: ?Sized> { 466 pub struct UniqueArc<T: ?Sized> {
635 inner: Arc<T>, 467 inner: Arc<T>,
636 } 468 }
637 469
638 impl<T> UniqueArc<T> { 470 impl<T> UniqueArc<T> {
639 /// Tries to allocate a new [`UniqueArc`] 471 /// Tries to allocate a new [`UniqueArc`] instance.
640 pub fn new(value: T, flags: Flags) -> Resu !! 472 pub fn try_new(value: T) -> Result<Self> {
641 Ok(Self { 473 Ok(Self {
642 // INVARIANT: The newly-created ob !! 474 // INVARIANT: The newly-created object has a ref-count of 1.
643 inner: Arc::new(value, flags)?, !! 475 inner: Arc::try_new(value)?,
644 }) 476 })
645 } 477 }
646 478
647 /// Tries to allocate a new [`UniqueArc`] 479 /// Tries to allocate a new [`UniqueArc`] instance whose contents are not initialised yet.
648 pub fn new_uninit(flags: Flags) -> Result< !! 480 pub fn try_new_uninit() -> Result<UniqueArc<MaybeUninit<T>>> {
649 // INVARIANT: The refcount is initiali !! 481 Ok(UniqueArc::<MaybeUninit<T>> {
650 let inner = Box::try_init::<AllocError !! 482 // INVARIANT: The newly-created object has a ref-count of 1.
651 try_init!(ArcInner { !! 483 inner: Arc::try_new(MaybeUninit::uninit())?,
652 // SAFETY: There are no safety <<
653 refcount: Opaque::new(unsafe { <<
654 data <- init::uninit::<T, Allo <<
655 }? AllocError), <<
656 flags, <<
657 )?; <<
658 Ok(UniqueArc { <<
659 // INVARIANT: The newly-created ob <<
660 // SAFETY: The pointer from the `B <<
661 inner: unsafe { Arc::from_inner(Bo <<
662 }) 484 })
663 } 485 }
664 } 486 }
665 487
666 impl<T> UniqueArc<MaybeUninit<T>> { 488 impl<T> UniqueArc<MaybeUninit<T>> {
667 /// Converts a `UniqueArc<MaybeUninit<T>>` 489 /// Converts a `UniqueArc<MaybeUninit<T>>` into a `UniqueArc<T>` by writing a value into it.
668 pub fn write(mut self, value: T) -> Unique 490 pub fn write(mut self, value: T) -> UniqueArc<T> {
669 self.deref_mut().write(value); 491 self.deref_mut().write(value);
670 // SAFETY: We just wrote the value to <<
671 unsafe { self.assume_init() } <<
672 } <<
673 <<
674 /// Unsafely assume that `self` is initial <<
675 /// <<
676 /// # Safety <<
677 /// <<
678 /// The caller guarantees that the value b <<
679 /// *immediate* UB to call this when the v <<
680 pub unsafe fn assume_init(self) -> UniqueA <<
681 let inner = ManuallyDrop::new(self).in 492 let inner = ManuallyDrop::new(self).inner.ptr;
682 UniqueArc { 493 UniqueArc {
683 // SAFETY: The new `Arc` is taking 494 // SAFETY: The new `Arc` is taking over `ptr` from `self.inner` (which won't be
684 // dropped). The types are compati 495 // dropped). The types are compatible because `MaybeUninit<T>` is compatible with `T`.
685 inner: unsafe { Arc::from_inner(in 496 inner: unsafe { Arc::from_inner(inner.cast()) },
686 } 497 }
687 } 498 }
688 <<
689 /// Initialize `self` using the given init <<
690 pub fn init_with<E>(mut self, init: impl I <<
691 // SAFETY: The supplied pointer is val <<
692 match unsafe { init.__init(self.as_mut <<
693 // SAFETY: Initialization complete <<
694 Ok(()) => Ok(unsafe { self.assume_ <<
695 Err(err) => Err(err), <<
696 } <<
697 } <<
698 <<
699 /// Pin-initialize `self` using the given <<
700 pub fn pin_init_with<E>( <<
701 mut self, <<
702 init: impl PinInit<T, E>, <<
703 ) -> core::result::Result<Pin<UniqueArc<T> <<
704 // SAFETY: The supplied pointer is val <<
705 // to ensure it does not move. <<
706 match unsafe { init.__pinned_init(self <<
707 // SAFETY: Initialization complete <<
708 Ok(()) => Ok(unsafe { self.assume_ <<
709 Err(err) => Err(err), <<
710 } <<
711 } <<
712 } 499 }
713 500
714 impl<T: ?Sized> From<UniqueArc<T>> for Pin<Uni 501 impl<T: ?Sized> From<UniqueArc<T>> for Pin<UniqueArc<T>> {
715 fn from(obj: UniqueArc<T>) -> Self { 502 fn from(obj: UniqueArc<T>) -> Self {
716 // SAFETY: It is not possible to move/ 503 // SAFETY: It is not possible to move/replace `T` inside a `Pin<UniqueArc<T>>` (unless `T`
717 // is `Unpin`), so it is ok to convert 504 // is `Unpin`), so it is ok to convert it to `Pin<UniqueArc<T>>`.
718 unsafe { Pin::new_unchecked(obj) } 505 unsafe { Pin::new_unchecked(obj) }
719 } 506 }
720 } 507 }
721 508
722 impl<T: ?Sized> Deref for UniqueArc<T> { 509 impl<T: ?Sized> Deref for UniqueArc<T> {
723 type Target = T; 510 type Target = T;
724 511
725 fn deref(&self) -> &Self::Target { 512 fn deref(&self) -> &Self::Target {
726 self.inner.deref() 513 self.inner.deref()
727 } 514 }
728 } 515 }
729 516
730 impl<T: ?Sized> DerefMut for UniqueArc<T> { 517 impl<T: ?Sized> DerefMut for UniqueArc<T> {
731 fn deref_mut(&mut self) -> &mut Self::Targ 518 fn deref_mut(&mut self) -> &mut Self::Target {
732 // SAFETY: By the `Arc` type invariant 519 // SAFETY: By the `Arc` type invariant, there is necessarily a reference to the object, so
733 // it is safe to dereference it. Addit 520 // it is safe to dereference it. Additionally, we know there is only one reference when
734 // it's inside a `UniqueArc`, so it is 521 // it's inside a `UniqueArc`, so it is safe to get a mutable reference.
735 unsafe { &mut self.inner.ptr.as_mut(). 522 unsafe { &mut self.inner.ptr.as_mut().data }
736 } <<
737 } <<
738 <<
739 impl<T: fmt::Display + ?Sized> fmt::Display fo <<
740 fn fmt(&self, f: &mut fmt::Formatter<'_>) <<
741 fmt::Display::fmt(self.deref(), f) <<
742 } <<
743 } <<
744 <<
745 impl<T: fmt::Display + ?Sized> fmt::Display fo <<
746 fn fmt(&self, f: &mut fmt::Formatter<'_>) <<
747 fmt::Display::fmt(self.deref(), f) <<
748 } <<
749 } <<
750 <<
751 impl<T: fmt::Debug + ?Sized> fmt::Debug for Un <<
752 fn fmt(&self, f: &mut fmt::Formatter<'_>) <<
753 fmt::Debug::fmt(self.deref(), f) <<
754 } <<
755 } <<
756 <<
757 impl<T: fmt::Debug + ?Sized> fmt::Debug for Ar <<
758 fn fmt(&self, f: &mut fmt::Formatter<'_>) <<
759 fmt::Debug::fmt(self.deref(), f) <<
760 } 523 }
761 } 524 }
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