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879f437248
The existing `CondVar` abstraction is a wrapper around `wait_queue_head`, but it does not support all use-cases of the C `wait_queue_head` type. To be specific, a `CondVar` cannot be registered with a `struct poll_table`. This limitation has the advantage that you do not need to call `synchronize_rcu` when destroying a `CondVar`. However, we need the ability to register a `poll_table` with a `wait_queue_head` in Rust Binder. To enable this, introduce a type called `PollCondVar`, which is like `CondVar` except that you can register a `poll_table`. We also introduce `PollTable`, which is a safe wrapper around `poll_table` that is intended to be used with `PollCondVar`. The destructor of `PollCondVar` unconditionally calls `synchronize_rcu` to ensure that the removal of epoll waiters has fully completed before the `wait_queue_head` is destroyed. That said, `synchronize_rcu` is rather expensive and is not needed in all cases: If we have never registered a `poll_table` with the `wait_queue_head`, then we don't need to call `synchronize_rcu`. (And this is a common case in Binder - not all processes use Binder with epoll.) The current implementation does not account for this, but if we find that it is necessary to improve this, a future patch could store a boolean next to the `wait_queue_head` to keep track of whether a `poll_table` has ever been registered. Reviewed-by: Benno Lossin <benno.lossin@proton.me> Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com> Signed-off-by: Alice Ryhl <aliceryhl@google.com> Bug: 324206405 Link: https://lore.kernel.org/all/20240209-alice-file-v5-9-a37886783025@google.com/ Change-Id: Ib6d2d7d2d62758b54351e94bf568fead6c3ed51c Signed-off-by: Alice Ryhl <aliceryhl@google.com>
62 lines
1.6 KiB
Rust
62 lines
1.6 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Synchronisation primitives.
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//!
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//! This module contains the kernel APIs related to synchronisation that have been ported or
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//! wrapped for usage by Rust code in the kernel.
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use crate::types::Opaque;
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mod arc;
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mod condvar;
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pub mod lock;
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mod locked_by;
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pub mod poll;
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pub use arc::{Arc, ArcBorrow, UniqueArc};
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pub use condvar::{CondVar, CondVarTimeoutResult};
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pub use lock::{mutex::Mutex, spinlock::SpinLock};
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pub use locked_by::LockedBy;
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/// Represents a lockdep class. It's a wrapper around C's `lock_class_key`.
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#[repr(transparent)]
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pub struct LockClassKey(Opaque<bindings::lock_class_key>);
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// SAFETY: `bindings::lock_class_key` is designed to be used concurrently from multiple threads and
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// provides its own synchronization.
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unsafe impl Sync for LockClassKey {}
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impl LockClassKey {
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/// Creates a new lock class key.
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pub const fn new() -> Self {
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Self(Opaque::uninit())
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}
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pub(crate) fn as_ptr(&self) -> *mut bindings::lock_class_key {
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self.0.get()
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}
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}
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/// Defines a new static lock class and returns a pointer to it.
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#[doc(hidden)]
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#[macro_export]
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macro_rules! static_lock_class {
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() => {{
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static CLASS: $crate::sync::LockClassKey = $crate::sync::LockClassKey::new();
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&CLASS
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}};
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}
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/// Returns the given string, if one is provided, otherwise generates one based on the source code
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/// location.
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#[doc(hidden)]
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#[macro_export]
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macro_rules! optional_name {
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() => {
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$crate::c_str!(::core::concat!(::core::file!(), ":", ::core::line!()))
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};
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($name:literal) => {
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$crate::c_str!($name)
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};
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}
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