// SPDX-License-Identifier: GPL-2.0 // Copyright (C) 2024 Google LLC. //! Version of `MmWithUser` using `mmput_async`. //! //! This is a separate file from `mm.rs` due to the dependency on `CONFIG_MMU=y`. #![cfg(CONFIG_MMU)] use crate::{ bindings, mm::MmWithUser, types::{ARef, AlwaysRefCounted}, }; use core::{ops::Deref, ptr::NonNull}; /// A wrapper for the kernel's `struct mm_struct`. /// /// This type is identical to `MmWithUser` except that it uses `mmput_async` when dropping a /// refcount. This means that the destructor of `ARef<MmWithUserAsync>` is safe to call in atomic /// context. /// /// # Invariants /// /// Values of this type are always refcounted using `mmget`. The value of `mm_users` is non-zero. #[repr(transparent)] pub struct MmWithUserAsync { mm: MmWithUser, } // SAFETY: It is safe to call `mmput_async` on another thread than where `mmget` was called. unsafe impl Send for MmWithUserAsync {} // SAFETY: All methods on `MmWithUserAsync` can be called in parallel from several threads. unsafe impl Sync for MmWithUserAsync {} // SAFETY: By the type invariants, this type is always refcounted. unsafe impl AlwaysRefCounted for MmWithUserAsync { #[inline] fn inc_ref(&self) { // SAFETY: The pointer is valid since self is a reference. unsafe { bindings::mmget(self.as_raw()) }; } #[inline] unsafe fn dec_ref(obj: NonNull<Self>) { // SAFETY: The caller is giving up their refcount. unsafe { bindings::mmput_async(obj.cast().as_ptr()) }; } } // Make all `MmWithUser` methods available on `MmWithUserAsync`. impl Deref for MmWithUserAsync { type Target = MmWithUser; #[inline] fn deref(&self) -> &MmWithUser { &self.mm } } impl MmWithUser { /// Use `mmput_async` when dropping this refcount. #[inline] pub fn into_mmput_async(me: ARef<MmWithUser>) -> ARef<MmWithUserAsync> { // SAFETY: The layouts and invariants are compatible. unsafe { ARef::from_raw(ARef::into_raw(me).cast()) } } }