projects/linux·blob master · refs

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1// SPDX-License-Identifier: GPL-2.0
2
3// Copyright (C) 2024 Google LLC.
4
5//! Utilities for working with `struct poll_table`.
6
7use crate::{
8 alloc::AllocError,
9 bindings,
10 fs::File,
11 prelude::*,
12 sync::{
13 rcu::synchronize_rcu,
14 CondVar,
15 LockClassKey, //
16 }, //
17 types::Opaque, //
18};
19use core::{
20 marker::PhantomData,
21 mem::ManuallyDrop,
22 ops::Deref, //
23};
24
25/// Creates a [`PollCondVar`] initialiser with the given name and a newly-created lock class.
26#[macro_export]
27macro_rules! new_poll_condvar {
28 ($($name:literal)?) => {
29 $crate::sync::poll::PollCondVar::new(
30 $crate::optional_name!($($name)?), $crate::static_lock_class!()
31 )
32 };
33}
34
35/// Wraps the kernel's `poll_table`.
36///
37/// # Invariants
38///
39/// The pointer must be null or reference a valid `poll_table`.
40#[repr(transparent)]
41pub struct PollTable<'a> {
42 table: *mut bindings::poll_table,
43 _lifetime: PhantomData<&'a bindings::poll_table>,
44}
45
46impl<'a> PollTable<'a> {
47 /// Creates a [`PollTable`] from a valid pointer.
48 ///
49 /// # Safety
50 ///
51 /// The pointer must be null or reference a valid `poll_table` for the duration of `'a`.
52 pub unsafe fn from_raw(table: *mut bindings::poll_table) -> Self {
53 // INVARIANTS: The safety requirements are the same as the struct invariants.
54 PollTable {
55 table,
56 _lifetime: PhantomData,
57 }
58 }
59
60 /// Register this [`PollTable`] with the provided [`PollCondVar`], so that it can be notified
61 /// using the condition variable.
62 pub fn register_wait(&self, file: &File, cv: &PollCondVar) {
63 // SAFETY:
64 // * `file.as_ptr()` references a valid file for the duration of this call.
65 // * `self.table` is null or references a valid poll_table for the duration of this call.
66 // * Since `PollCondVar` is pinned, its destructor is guaranteed to run before the memory
67 // containing `cv.wait_queue_head` is invalidated. Since the destructor clears all
68 // waiters and then waits for an rcu grace period, it's guaranteed that
69 // `cv.wait_queue_head` remains valid for at least an rcu grace period after the removal
70 // of the last waiter.
71 unsafe { bindings::poll_wait(file.as_ptr(), cv.wait_queue_head.get(), self.table) }
72 }
73}
74
75/// A wrapper around [`CondVar`] that makes it usable with [`PollTable`].
76///
77/// [`CondVar`]: crate::sync::CondVar
78#[pin_data(PinnedDrop)]
79#[repr(transparent)]
80pub struct PollCondVar {
81 #[pin]
82 inner: CondVar,
83}
84
85impl PollCondVar {
86 /// Constructs a new condvar initialiser.
87 pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> impl PinInit<Self> {
88 pin_init!(Self {
89 inner <- CondVar::new(name, key),
90 })
91 }
92}
93
94// Make the `CondVar` methods callable on `PollCondVar`.
95impl Deref for PollCondVar {
96 type Target = CondVar;
97
98 fn deref(&self) -> &CondVar {
99 &self.inner
100 }
101}
102
103#[pinned_drop]
104impl PinnedDrop for PollCondVar {
105 #[inline]
106 fn drop(self: Pin<&mut Self>) {
107 // Clear anything registered using `register_wait`.
108 //
109 // SAFETY: The pointer points at a valid `wait_queue_head`.
110 unsafe { bindings::__wake_up_pollfree(self.inner.wait_queue_head.get()) };
111
112 // Wait for epoll items to be properly removed.
113 synchronize_rcu();
114 }
115}
116
117/// A [`KBox<PollCondVar>`] that uses `kfree_rcu`.
118///
119/// [`KBox<PollCondVar>`]: PollCondVar
120pub struct PollCondVarBox {
121 inner: ManuallyDrop<Pin<KBox<PollCondVarBoxInner>>>,
122}
123
124#[pin_data]
125#[repr(C)]
126struct PollCondVarBoxInner {
127 #[pin]
128 inner: PollCondVar,
129 rcu: Opaque<bindings::kvfree_rcu_head>,
130}
131
132// SAFETY: PollCondVar is Send
133unsafe impl Send for PollCondVarBoxInner {}
134// SAFETY: PollCondVar is Sync
135unsafe impl Sync for PollCondVarBoxInner {}
136
137impl PollCondVarBox {
138 /// Constructs a new boxed [`PollCondVar`].
139 pub fn new(name: &'static CStr, key: Pin<&'static LockClassKey>) -> Result<Self, AllocError> {
140 let b = KBox::pin_init(
141 pin_init!(PollCondVarBoxInner {
142 inner <- PollCondVar::new(name, key),
143 rcu: Opaque::uninit(),
144 }),
145 GFP_KERNEL,
146 )
147 .map_err(|_| AllocError)?;
148
149 Ok(PollCondVarBox {
150 inner: ManuallyDrop::new(b),
151 })
152 }
153}
154
155impl Deref for PollCondVarBox {
156 type Target = PollCondVar;
157 fn deref(&self) -> &PollCondVar {
158 &self.inner.inner
159 }
160}
161
162impl Drop for PollCondVarBox {
163 #[inline]
164 fn drop(&mut self) {
165 // SAFETY: ManuallyDrop::take ok because not already taken.
166 let boxed = unsafe { ManuallyDrop::take(&mut self.inner) };
167
168 // SAFETY: The code below frees the box without calling the actual destructor of the type,
169 // but it's okay because it re-implements the destructor using `kfree_rcu()` in place of
170 // `synchronize_rcu()`.
171 let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(boxed) });
172
173 // SAFETY: The pointer points at a valid `wait_queue_head`.
174 unsafe { bindings::__wake_up_pollfree((*ptr).inner.inner.wait_queue_head.get()) };
175
176 // SAFETY: This was allocated using `KBox::pin_init`, so it can be freed with `kvfree`.
177 unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
178 }
179}