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Prefer ManuallyDrop than mem::forget

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This commit is contained in:
Ruihan Li
2024-06-06 09:35:32 +08:00
committed by Tate, Hongliang Tian
parent 7966719e6a
commit e9330eea7d
2 changed files with 45 additions and 24 deletions
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22
ostd/src/mm/page/mod.rs
View File

@ -116,6 +116,17 @@ impl<M: PageMeta> Page<M> {
}
}
/// Increase the reference count of the page by one.
///
/// # Safety
///
/// The physical address must represent a valid page and the caller must already hold one
/// reference count.
pub(in crate::mm) unsafe fn inc_ref(paddr: Paddr) {
let page = unsafe { ManuallyDrop::new(Self::from_raw(paddr)) };
let _page = page.clone();
}
/// Get the physical address.
pub fn paddr(&self) -> Paddr {
mapping::meta_to_page::<PagingConsts>(self.ptr as Vaddr)
@ -211,6 +222,17 @@ impl DynPage {
Self { ptr }
}
/// Increase the reference count of the page by one.
///
/// # Safety
///
/// The physical address must represent a valid page and the caller must already hold one
/// reference count.
pub(in crate::mm) unsafe fn inc_ref(paddr: Paddr) {
let page = unsafe { ManuallyDrop::new(Self::from_raw(paddr)) };
let _page = page.clone();
}
/// Get the physical address of the start of the page
pub fn paddr(&self) -> Paddr {
mapping::meta_to_page::<PagingConsts>(self.ptr as Vaddr)

47
ostd/src/mm/page_table/node.rs
View File

@ -69,10 +69,13 @@ where
/// Converts a raw handle to an accessible handle by pertaining the lock.
pub(super) fn lock(self) -> PageTableNode<E, C> {
// Prevent dropping the handle.
let this = ManuallyDrop::new(self);
// SAFETY: The physical address in the raw handle is valid and we are
// transferring the ownership to a new handle. No increment of the reference
// count is needed.
let page = unsafe { Page::<PageTablePageMeta<E, C>>::from_raw(self.paddr()) };
let page = unsafe { Page::<PageTablePageMeta<E, C>>::from_raw(this.paddr()) };
// Acquire the lock.
while page
@ -84,9 +87,6 @@ where
core::hint::spin_loop();
}
// Prevent dropping the handle.
let _ = ManuallyDrop::new(self);
PageTableNode::<E, C> { page }
}
@ -149,11 +149,11 @@ where
}
fn inc_ref(&self) {
// SAFETY: The physical address in the raw handle is valid and we are
// incrementing the reference count by cloning and forgetting.
let page = unsafe { Page::<PageTablePageMeta<E, C>>::from_raw(self.paddr()) };
core::mem::forget(page.clone());
core::mem::forget(page);
// SAFETY: We have a reference count to the page and can safely increase the reference
// count by one more.
unsafe {
Page::<PageTablePageMeta<E, C>>::inc_ref(self.paddr());
}
}
}
@ -264,24 +264,22 @@ where
} else {
let paddr = pte.paddr();
if !pte.is_last(self.level()) {
// SAFETY: The physical address is recorded in a valid PTE
// which would be casted from a handle. We are incrementing
// the reference count so we restore, clone, and forget both.
let node = unsafe { Page::<PageTablePageMeta<E, C>>::from_raw(paddr) };
let inc_ref = node.clone();
core::mem::forget(node);
core::mem::forget(inc_ref);
// SAFETY: We have a reference count to the page and can safely increase the reference
// count by one more.
unsafe {
Page::<PageTablePageMeta<E, C>>::inc_ref(paddr);
}
Child::PageTable(RawPageTableNode {
raw: paddr,
_phantom: PhantomData,
})
} else if in_tracked_range {
// SAFETY: The physical address is recorded in a valid PTE
// which would be casted from a handle. We are incrementing
// the reference count so we restore and forget a cloned one.
let page = unsafe { DynPage::from_raw(paddr) };
core::mem::forget(page.clone());
Child::Page(page)
// SAFETY: We have a reference count to the page and can safely increase the reference
// count by one more.
unsafe {
DynPage::inc_ref(paddr);
}
Child::Page(unsafe { DynPage::from_raw(paddr) })
} else {
Child::Untracked(paddr)
}
@ -358,10 +356,11 @@ where
// They should be ensured by the cursor.
debug_assert!(idx < nr_subpage_per_huge::<C>());
// The ownership is transferred to a raw PTE. Don't drop the handle.
let pt = ManuallyDrop::new(pt);
let pte = Some(E::new_pt(pt.paddr()));
self.overwrite_pte(idx, pte, in_tracked_range);
// The ownership is transferred to a raw PTE. Don't drop the handle.
let _ = ManuallyDrop::new(pt);
}
/// Map a page at a given index.