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switch Rcu to the arcu crate

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The arcu crate is a more general implementation of the Rcu I implemented in here in scryer. It contains some bug-fixes regarding race-conditions in the Rcu update function, which could cause leaks and uses after free.

Source of the problem was the Relaxed load/strore/update of the reference count in side the Arc not being properly ordered with other load/stores.
This commit is contained in:
Bennet Bleßmann
2024-07-06 14:49:19 +02:00
parent fcb41542c3
commit d87400afa0
6 changed files with 41 additions and 249 deletions
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44
src/atom_table.rs
View File

@@ -2,7 +2,6 @@
use crate::parser::ast::MAX_ARITY;
use crate::raw_block::*;
use crate::rcu::{Rcu, RcuRef};
use crate::types::*;
use std::cmp::Ordering;
@@ -16,6 +15,10 @@ use std::sync::Mutex;
use std::sync::RwLock;
use std::sync::Weak;
use arcu::atomic::Arcu;
use arcu::epoch_counters::GlobalEpochCounterPool;
use arcu::rcu_ref::RcuRef;
use arcu::Rcu;
use indexmap::IndexSet;
use scryer_modular_bitfield::prelude::*;
@@ -180,7 +183,7 @@ impl Atom {
let atom_table =
arc_atom_table().expect("We should only have an Atom while there is an AtomTable");
AtomTableRef::try_map(atom_table.inner.active_epoch(), |buf| unsafe {
AtomTableRef::try_map(atom_table.inner.read(), |buf| unsafe {
let ptr = buf
.block
.base
@@ -278,17 +281,17 @@ impl Ord for Atom {
#[derive(Debug)]
pub struct InnerAtomTable {
block: RawBlock<AtomTable>,
pub table: Rcu<IndexSet<Atom>>,
pub table: Arcu<IndexSet<Atom>, GlobalEpochCounterPool>,
}
#[derive(Debug)]
pub struct AtomTable {
inner: Rcu<InnerAtomTable>,
inner: Arcu<InnerAtomTable, GlobalEpochCounterPool>,
// this lock is taking during resizing
update: Mutex<()>,
}
pub type AtomTableRef<M> = RcuRef<InnerAtomTable, M>;
pub type AtomTableRef<M> = arcu::rcu_ref::RcuRef<InnerAtomTable, M>;
impl InnerAtomTable {
#[inline(always)]
@@ -296,7 +299,7 @@ impl InnerAtomTable {
STATIC_ATOMS_MAP
.get(string)
.cloned()
.or_else(|| self.table.active_epoch().get(string).cloned())
.or_else(|| self.table.read().get(string).cloned())
}
}
@@ -314,10 +317,13 @@ impl AtomTable {
atom_table
} else {
let atom_table = Arc::new(Self {
inner: Rcu::new(InnerAtomTable {
block: RawBlock::new(),
table: Rcu::new(IndexSet::new()),
}),
inner: Arcu::new(
InnerAtomTable {
block: RawBlock::new(),
table: Arcu::new(IndexSet::new(), GlobalEpochCounterPool),
},
GlobalEpochCounterPool,
),
update: Mutex::new(()),
});
*guard = Arc::downgrade(&atom_table);
@@ -327,13 +333,13 @@ impl AtomTable {
}
pub fn active_table(&self) -> RcuRef<IndexSet<Atom>, IndexSet<Atom>> {
self.inner.active_epoch().table.active_epoch()
self.inner.read().table.read()
}
pub fn build_with(atom_table: &AtomTable, string: &str) -> Atom {
loop {
let mut block_epoch = atom_table.inner.active_epoch();
let mut table_epoch = block_epoch.table.active_epoch();
let mut block_epoch = atom_table.inner.read();
let mut table_epoch = block_epoch.table.read();
if let Some(atom) = block_epoch.lookup_str(string) {
return atom;
@@ -342,10 +348,8 @@ impl AtomTable {
// take a lock to prevent concurrent updates
let update_guard = atom_table.update.lock().unwrap();
let is_same_allocation =
RcuRef::same_epoch(&block_epoch, &atom_table.inner.active_epoch());
let is_same_atom_list =
RcuRef::same_epoch(&table_epoch, &block_epoch.table.active_epoch());
let is_same_allocation = RcuRef::same_epoch(&block_epoch, &atom_table.inner.read());
let is_same_atom_list = RcuRef::same_epoch(&table_epoch, &block_epoch.table.read());
if !(is_same_allocation && is_same_atom_list) {
// some other thread raced us between our lookup and
@@ -364,14 +368,14 @@ impl AtomTable {
if ptr.is_null() {
// garbage collection would go here
let new_block = block_epoch.block.grow_new().unwrap();
let new_table = Rcu::new(table_epoch.clone());
let new_table = Arcu::new(table_epoch.clone(), GlobalEpochCounterPool);
let new_alloc = InnerAtomTable {
block: new_block,
table: new_table,
};
atom_table.inner.replace(new_alloc);
block_epoch = atom_table.inner.active_epoch();
table_epoch = block_epoch.table.active_epoch();
block_epoch = atom_table.inner.read();
table_epoch = block_epoch.table.read();
} else {
break ptr;
}