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rust/bql: Ensure BQL locked early at BqlRefCell borrowing

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At present, BqlRefCell checks whether BQL is locked when it blocks BQL
unlock (in bql_block_unlock).

But the such check should be done earlier - at the beginning of
BqlRefCell borrowing.

So convert BqlRefCell::borrow field from Cell<> to BqlCell<>, to
guarantee BQL is locked from the beginning when someone is trying to
borrow BqlRefCell.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20251113051937.4017675-6-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Zhao Liu
2025-11-13 13:19:20 +08:00
committed by Paolo Bonzini
parent febdab3d5d
commit 0118c2d7e8
1 changed files with 9 additions and 7 deletions
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16
rust/bql/src/cell.rs
View File

@@ -142,8 +142,10 @@
//! Multiple immutable borrows are allowed via [`borrow`](BqlRefCell::borrow),
//! or a single mutable borrow via [`borrow_mut`](BqlRefCell::borrow_mut). The
//! thread will panic if these rules are violated or if the BQL is not held.
#[cfg(feature = "debug_cell")]
use std::cell::Cell;
use std::{
cell::{Cell, UnsafeCell},
cell::UnsafeCell,
cmp::Ordering,
fmt,
marker::PhantomData,
@@ -378,7 +380,7 @@ pub struct BqlRefCell<T> {
// for std::cell::BqlRefCell), so that we can use offset_of! on it.
// UnsafeCell and repr(C) both prevent usage of niches.
value: UnsafeCell<T>,
borrow: Cell<BorrowFlag>,
borrow: BqlCell<BorrowFlag>,
// Stores the location of the earliest currently active borrow.
// This gets updated whenever we go from having zero borrows
// to having a single borrow. When a borrow occurs, this gets included
@@ -427,7 +429,7 @@ impl<T> BqlRefCell<T> {
pub const fn new(value: T) -> BqlRefCell<T> {
BqlRefCell {
value: UnsafeCell::new(value),
borrow: Cell::new(UNUSED),
borrow: BqlCell::new(UNUSED),
#[cfg(feature = "debug_cell")]
borrowed_at: Cell::new(None),
}
@@ -689,12 +691,12 @@ impl<T> From<T> for BqlRefCell<T> {
}
struct BorrowRef<'b> {
borrow: &'b Cell<BorrowFlag>,
borrow: &'b BqlCell<BorrowFlag>,
}
impl<'b> BorrowRef<'b> {
#[inline]
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRef<'b>> {
fn new(borrow: &'b BqlCell<BorrowFlag>) -> Option<BorrowRef<'b>> {
let b = borrow.get().wrapping_add(1);
if !is_reading(b) {
// Incrementing borrow can result in a non-reading value (<= 0) in these cases:
@@ -790,12 +792,12 @@ impl<T: fmt::Display> fmt::Display for BqlRef<'_, T> {
}
struct BorrowRefMut<'b> {
borrow: &'b Cell<BorrowFlag>,
borrow: &'b BqlCell<BorrowFlag>,
}
impl<'b> BorrowRefMut<'b> {
#[inline]
fn new(borrow: &'b Cell<BorrowFlag>) -> Option<BorrowRefMut<'b>> {
fn new(borrow: &'b BqlCell<BorrowFlag>) -> Option<BorrowRefMut<'b>> {
// There must currently be no existing references when borrow_mut() is
// called, so we explicitly only allow going from UNUSED to UNUSED - 1.
match borrow.get() {