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//! Version of `MmWithUser` using `mmput_async`.
6//!
7//! This is a separate file from `mm.rs` due to the dependency on `CONFIG_MMU=y`.
8#![cfg(CONFIG_MMU)]
9
10use crate::{
11 bindings,
12 mm::MmWithUser,
13 sync::aref::{ARef, AlwaysRefCounted},
14};
15use core::{ops::Deref, ptr::NonNull};
16
17/// A wrapper for the kernel's `struct mm_struct`.
18///
19/// This type is identical to `MmWithUser` except that it uses `mmput_async` when dropping a
20/// refcount. This means that the destructor of `ARef<MmWithUserAsync>` is safe to call in atomic
21/// context.
22///
23/// # Invariants
24///
25/// Values of this type are always refcounted using `mmget`. The value of `mm_users` is non-zero.
26#[repr(transparent)]
27pub struct MmWithUserAsync {
28 mm: MmWithUser,
29}
30
31// SAFETY: It is safe to call `mmput_async` on another thread than where `mmget` was called.
32unsafe impl Send for MmWithUserAsync {}
33// SAFETY: All methods on `MmWithUserAsync` can be called in parallel from several threads.
34unsafe impl Sync for MmWithUserAsync {}
35
36// SAFETY: By the type invariants, this type is always refcounted.
37unsafe impl AlwaysRefCounted for MmWithUserAsync {
38 #[inline]
39 fn inc_ref(&self) {
40 // SAFETY: The pointer is valid since self is a reference.
41 unsafe { bindings::mmget(self.as_raw()) };
42 }
43
44 #[inline]
45 unsafe fn dec_ref(obj: NonNull<Self>) {
46 // SAFETY: The caller is giving up their refcount.
47 unsafe { bindings::mmput_async(obj.cast().as_ptr()) };
48 }
49}
50
51// Make all `MmWithUser` methods available on `MmWithUserAsync`.
52impl Deref for MmWithUserAsync {
53 type Target = MmWithUser;
54
55 #[inline]
56 fn deref(&self) -> &MmWithUser {
57 &self.mm
58 }
59}
60
61impl MmWithUser {
62 /// Use `mmput_async` when dropping this refcount.
63 #[inline]
64 pub fn into_mmput_async(me: ARef<MmWithUser>) -> ARef<MmWithUserAsync> {
65 // SAFETY: The layouts and invariants are compatible.
66 unsafe { ARef::from_raw(ARef::into_raw(me).cast()) }
67 }
68}