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Fork choice bug fixes (#449)

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* Change reduced tree for adding weightless node

* Add more comments for reduced tree fork choice

* Small refactor on reduced tree for readability

* Move test_harness forking logic into itself

* Add new `AncestorIter` trait to store

* Add unfinished tests to fork choice

* Make `beacon_state.genesis_block_root` public

* Add failing lmd_ghost fork choice tests

* Extend fork_choice tests, create failing test

* Implement Debug for generic ReducedTree

* Add lazy_static to fork choice tests

* Add verify_integrity fn to reduced tree

* Fix bugs in reduced tree

* Ensure all reduced tree tests verify integrity

* Slightly alter reduce tree test params

* Add (failing) reduced tree test

* Fix bug in fork choice

Iter ancestors was not working well with skip slots

* Put maximum depth for common ancestor search

Ensures that we don't search back past the finalized root.

* Add basic finalization tests for reduced tree

* Change fork choice to use beacon_block_root

Previously it was using target_root, which was wrong

* Make ancestor iter return option

* Disable fork choice test when !debug_assertions

* Fix type, removed code fragment

* Tidy some borrow-checker evading

* Lower reduced tree random test iterations
This commit is contained in:
Paul Hauner
2019-07-29 12:08:52 +10:00
committed by GitHub
parent 6de9e5bd6f
commit 7458022fcf
8 changed files with 673 additions and 141 deletions
Download Patch File Download Diff File Expand all files Collapse all files

358
eth2/lmd_ghost/src/reduced_tree.rs
View File

@@ -6,9 +6,10 @@
use super::{LmdGhost, Result as SuperResult};
use parking_lot::RwLock;
use std::collections::HashMap;
use std::fmt;
use std::marker::PhantomData;
use std::sync::Arc;
use store::{iter::BestBlockRootsIterator, Error as StoreError, Store};
use store::{iter::BlockRootsIterator, Error as StoreError, Store};
use types::{BeaconBlock, BeaconState, EthSpec, Hash256, Slot};
type Result<T> = std::result::Result<T, Error>;
@@ -35,6 +36,23 @@ pub struct ThreadSafeReducedTree<T, E> {
core: RwLock<ReducedTree<T, E>>,
}
impl<T, E> fmt::Debug for ThreadSafeReducedTree<T, E> {
/// `Debug` just defers to the implementation of `self.core`.
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.core.fmt(f)
}
}
impl<T, E> ThreadSafeReducedTree<T, E>
where
T: Store,
E: EthSpec,
{
pub fn verify_integrity(&self) -> std::result::Result<(), String> {
self.core.read().verify_integrity()
}
}
impl<T, E> LmdGhost<T, E> for ThreadSafeReducedTree<T, E>
where
T: Store,
@@ -100,6 +118,12 @@ struct ReducedTree<T, E> {
_phantom: PhantomData<E>,
}
impl<T, E> fmt::Debug for ReducedTree<T, E> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
self.nodes.fmt(f)
}
}
impl<T, E> ReducedTree<T, E>
where
T: Store,
@@ -126,6 +150,10 @@ where
}
}
/// Set the root node (the node without any parents) to the given `new_slot` and `new_root`.
///
/// The given `new_root` must be in the block tree (but not necessarily in the reduced tree).
/// Any nodes which are not a descendant of `new_root` will be removed from the store.
pub fn update_root(&mut self, new_slot: Slot, new_root: Hash256) -> Result<()> {
if !self.nodes.contains_key(&new_root) {
let node = Node {
@@ -276,55 +304,54 @@ where
Ok(weight)
}
/// Removes the vote from `validator_index` from the reduced tree.
///
/// If the validator had a vote in the tree, the removal of that vote may cause a node to
/// become redundant and removed from the reduced tree.
fn remove_latest_message(&mut self, validator_index: usize) -> Result<()> {
if self.latest_votes.get(validator_index).is_some() {
// Unwrap is safe as prior `if` statements ensures the result is `Some`.
let vote = self.latest_votes.get(validator_index).unwrap();
if let Some(vote) = self.latest_votes.get(validator_index).clone() {
self.get_mut_node(vote.hash)?.remove_voter(validator_index);
let node = self.get_node(vote.hash)?.clone();
let should_delete = {
self.get_mut_node(vote.hash)?.remove_voter(validator_index);
let node = self.get_node(vote.hash)?.clone();
if let Some(parent_hash) = node.parent_hash {
if node.has_votes() || node.children.len() > 1 {
// A node with votes or more than one child is never removed.
} else if node.children.len() == 1 {
// A node which has only one child may be removed.
//
// Load the child of the node and set it's parent to be the parent of this
// node (viz., graft the node's child to the node's parent)
let child = self.get_mut_node(node.children[0])?;
child.parent_hash = node.parent_hash;
if let Some(parent_hash) = node.parent_hash {
if node.has_votes() || node.children.len() > 1 {
// A node with votes or more than one child is never removed.
false
} else if node.children.len() == 1 {
// A node which has only one child may be removed.
//
// Load the child of the node and set it's parent to be the parent of this
// node (viz., graft the node's child to the node's parent)
let child = self.get_mut_node(node.children[0])?;
child.parent_hash = node.parent_hash;
// Graft the parent of this node to it's child.
if let Some(parent_hash) = node.parent_hash {
let parent = self.get_mut_node(parent_hash)?;
parent.replace_child(node.block_hash, node.children[0])?;
}
true
} else if node.children.is_empty() {
// A node which has no children may be deleted and potentially it's parent
// too.
self.maybe_delete_node(parent_hash)?;
true
} else {
// It is impossible for a node to have a number of children that is not 0, 1 or
// greater than one.
//
// This code is strictly unnecessary, however we keep it for readability.
unreachable!();
// Graft the parent of this node to it's child.
if let Some(parent_hash) = node.parent_hash {
let parent = self.get_mut_node(parent_hash)?;
parent.replace_child(node.block_hash, node.children[0])?;
}
} else {
// A node without a parent is the genesis/finalized node and should never be removed.
false
}
};
if should_delete {
self.nodes.remove(&vote.hash);
self.nodes.remove(&vote.hash);
} else if node.children.is_empty() {
// Remove the to-be-deleted node from it's parent.
if let Some(parent_hash) = node.parent_hash {
self.get_mut_node(parent_hash)?
.remove_child(node.block_hash)?;
}
self.nodes.remove(&vote.hash);
// A node which has no children may be deleted and potentially it's parent
// too.
self.maybe_delete_node(parent_hash)?;
} else {
// It is impossible for a node to have a number of children that is not 0, 1 or
// greater than one.
//
// This code is strictly unnecessary, however we keep it for readability.
unreachable!();
}
} else {
// A node without a parent is the genesis/finalized node and should never be removed.
}
self.latest_votes.insert(validator_index, Some(vote));
@@ -333,23 +360,27 @@ where
Ok(())
}
/// Deletes a node if it is unnecessary.
///
/// Any node is unnecessary if all of the following are true:
///
/// - it is not the root node.
/// - it only has one child.
/// - it does not have any votes.
fn maybe_delete_node(&mut self, hash: Hash256) -> Result<()> {
let should_delete = {
let node = self.get_node(hash)?.clone();
if let Some(parent_hash) = node.parent_hash {
if (node.children.len() == 1) && !node.has_votes() {
// Graft the child to it's grandparent.
let child_hash = {
let child_node = self.get_mut_node(node.children[0])?;
child_node.parent_hash = node.parent_hash;
let child_hash = node.children[0];
child_node.block_hash
};
// Graft the single descendant `node` to the `parent` of node.
self.get_mut_node(child_hash)?.parent_hash = Some(parent_hash);
// Graft the grandparent to it's grandchild.
let parent_node = self.get_mut_node(parent_hash)?;
parent_node.replace_child(node.block_hash, child_hash)?;
// Detach `node` from `parent`, replacing it with `child`.
self.get_mut_node(parent_hash)?
.replace_child(hash, child_hash)?;
true
} else {
@@ -385,7 +416,7 @@ where
}
fn add_weightless_node(&mut self, slot: Slot, hash: Hash256) -> Result<()> {
if slot >= self.root_slot() && !self.nodes.contains_key(&hash) {
if slot > self.root_slot() && !self.nodes.contains_key(&hash) {
let node = Node {
block_hash: hash,
..Node::default()
@@ -393,6 +424,8 @@ where
self.add_node(node)?;
// Read the `parent_hash` from the newly created node. If it has a parent (i.e., it's
// not the root), see if it is superfluous.
if let Some(parent_hash) = self.get_node(hash)?.parent_hash {
self.maybe_delete_node(parent_hash)?;
}
@@ -401,75 +434,108 @@ where
Ok(())
}
/// Add `node` to the reduced tree, returning an error if `node` is not rooted in the tree.
fn add_node(&mut self, mut node: Node) -> Result<()> {
// Find the highest (by slot) ancestor of the given hash/block that is in the reduced tree.
let mut prev_in_tree = {
let hash = self
.find_prev_in_tree(node.block_hash)
.ok_or_else(|| Error::NotInTree(node.block_hash))?;
self.get_mut_node(hash)?.clone()
};
let mut added = false;
// Find the highest (by slot) ancestor of the given node in the reduced tree.
//
// If this node has no ancestor in the tree, exit early.
let mut prev_in_tree = self
.find_prev_in_tree(node.block_hash)
.ok_or_else(|| Error::NotInTree(node.block_hash))
.and_then(|hash| self.get_node(hash))?
.clone();
// If the ancestor of `node` has children, there are three possible operations:
//
// 1. Graft the `node` between two existing nodes.
// 2. Create another node that will be grafted between two existing nodes, then graft
// `node` to it.
// 3. Graft `node` to an existing node.
if !prev_in_tree.children.is_empty() {
for &child_hash in &prev_in_tree.children {
// 1. Graft the new node between two existing nodes.
//
// If `node` is a descendant of `prev_in_tree` but an ancestor of a child connected to
// `prev_in_tree`.
//
// This means that `node` can be grafted between `prev_in_tree` and the child that is a
// descendant of both `node` and `prev_in_tree`.
if self
.iter_ancestors(child_hash)?
.any(|(ancestor, _slot)| ancestor == node.block_hash)
{
let child = self.get_mut_node(child_hash)?;
// Graft `child` to `node`.
child.parent_hash = Some(node.block_hash);
// Graft `node` to `child`.
node.children.push(child_hash);
// Detach `child` from `prev_in_tree`, replacing it with `node`.
prev_in_tree.replace_child(child_hash, node.block_hash)?;
// Graft `node` to `prev_in_tree`.
node.parent_hash = Some(prev_in_tree.block_hash);
added = true;
break;
}
}
if !added {
// 2. Create another node that will be grafted between two existing nodes, then graft
// `node` to it.
//
// Note: given that `prev_in_tree` has children and that `node` is not an ancestor of
// any of the children of `prev_in_tree`, we know that `node` is on a different fork to
// all of the children of `prev_in_tree`.
if node.parent_hash.is_none() {
for &child_hash in &prev_in_tree.children {
// Find the highest (by slot) common ancestor between `node` and `child`.
//
// The common ancestor is the last block before `node` and `child` forked.
let ancestor_hash =
self.find_least_common_ancestor(node.block_hash, child_hash)?;
self.find_highest_common_ancestor(node.block_hash, child_hash)?;
// If the block before `node` and `child` forked is _not_ `prev_in_tree` we
// must add this new block into the tree (because it is a decision node
// between two forks).
if ancestor_hash != prev_in_tree.block_hash {
let child = self.get_mut_node(child_hash)?;
// Create a new `common_ancestor` node which represents the `ancestor_hash`
// block, has `prev_in_tree` as the parent and has both `node` and `child`
// as children.
let common_ancestor = Node {
block_hash: ancestor_hash,
parent_hash: Some(prev_in_tree.block_hash),
children: vec![node.block_hash, child_hash],
..Node::default()
};
// Graft `child` and `node` to `common_ancestor`.
child.parent_hash = Some(common_ancestor.block_hash);
node.parent_hash = Some(common_ancestor.block_hash);
prev_in_tree.replace_child(child_hash, ancestor_hash)?;
// Detach `child` from `prev_in_tree`, replacing it with `common_ancestor`.
prev_in_tree.replace_child(child_hash, common_ancestor.block_hash)?;
// Store the new `common_ancestor` node.
self.nodes
.insert(common_ancestor.block_hash, common_ancestor);
added = true;
break;
}
}
}
}
if !added {
if node.parent_hash.is_none() {
// 3. Graft `node` to an existing node.
//
// Graft `node` to `prev_in_tree` and `prev_in_tree` to `node`
node.parent_hash = Some(prev_in_tree.block_hash);
prev_in_tree.children.push(node.block_hash);
}
// Update `prev_in_tree`. A mutable reference was not maintained to satisfy the borrow
// checker.
//
// This is not an ideal solution and results in unnecessary memory copies -- a better
// solution is certainly possible.
// checker. Perhaps there's a better way?
self.nodes.insert(prev_in_tree.block_hash, prev_in_tree);
self.nodes.insert(node.block_hash, node);
@@ -485,62 +551,112 @@ where
.and_then(|(root, _slot)| Some(root))
}
/// For the given `child` block hash, return the block's ancestor at the given `target` slot.
fn find_ancestor_at_slot(&self, child: Hash256, target: Slot) -> Result<Hash256> {
let (root, slot) = self
.iter_ancestors(child)?
.find(|(_block, slot)| *slot <= target)
.ok_or_else(|| Error::NotInTree(child))?;
// Explicitly check that the slot is the target in the case that the given child has a slot
// above target.
if slot == target {
Ok(root)
} else {
Err(Error::NotInTree(child))
}
}
/// For the two given block roots (`a_root` and `b_root`), find the first block they share in
/// the tree. Viz, find the block that these two distinct blocks forked from.
fn find_least_common_ancestor(&self, a_root: Hash256, b_root: Hash256) -> Result<Hash256> {
// If the blocks behind `a_root` and `b_root` are not at the same slot, take the highest
// block (by slot) down to be equal with the lower slot.
//
// The result is two roots which identify two blocks at the same height.
let (a_root, b_root) = {
let a = self.get_block(a_root)?;
let b = self.get_block(b_root)?;
fn find_highest_common_ancestor(&self, a_root: Hash256, b_root: Hash256) -> Result<Hash256> {
let mut a_iter = self.iter_ancestors(a_root)?;
let mut b_iter = self.iter_ancestors(b_root)?;
if a.slot > b.slot {
(self.find_ancestor_at_slot(a_root, b.slot)?, b_root)
} else if b.slot > a.slot {
(a_root, self.find_ancestor_at_slot(b_root, a.slot)?)
} else {
(a_root, b_root)
// Combines the `next()` fns on the `a_iter` and `b_iter` and returns the roots of two
// blocks at the same slot, or `None` if we have gone past genesis or the root of this tree.
let mut iter_blocks_at_same_height = || -> Option<(Hash256, Hash256)> {
match (a_iter.next(), b_iter.next()) {
(Some((mut a_root, a_slot)), Some((mut b_root, b_slot))) => {
// If either of the slots are lower than the root of this tree, exit early.
if a_slot < self.root.1 || b_slot < self.root.1 {
None
} else {
if a_slot < b_slot {
for _ in a_slot.as_u64()..b_slot.as_u64() {
b_root = b_iter.next()?.0;
}
} else if a_slot > b_slot {
for _ in b_slot.as_u64()..a_slot.as_u64() {
a_root = a_iter.next()?.0;
}
}
Some((a_root, b_root))
}
}
_ => None,
}
};
let ((a_root, _a_slot), (_b_root, _b_slot)) = self
.iter_ancestors(a_root)?
.zip(self.iter_ancestors(b_root)?)
.find(|((a_root, _), (b_root, _))| a_root == b_root)
.ok_or_else(|| Error::NoCommonAncestor((a_root, b_root)))?;
Ok(a_root)
loop {
match iter_blocks_at_same_height() {
Some((a_root, b_root)) if a_root == b_root => break Ok(a_root),
Some(_) => (),
None => break Err(Error::NoCommonAncestor((a_root, b_root))),
}
}
}
fn iter_ancestors(&self, child: Hash256) -> Result<BestBlockRootsIterator<E, T>> {
fn iter_ancestors(&self, child: Hash256) -> Result<BlockRootsIterator<E, T>> {
let block = self.get_block(child)?;
let state = self.get_state(block.state_root)?;
Ok(BestBlockRootsIterator::owned(
Ok(BlockRootsIterator::owned(
self.store.clone(),
state,
block.slot - 1,
))
}
/// Verify the integrity of `self`. Returns `Ok(())` if the tree has integrity, otherwise returns `Err(description)`.
///
/// Tries to detect the following erroneous conditions:
///
/// - Dangling references inside the tree.
/// - Any scenario where there's not exactly one root node.
///
/// ## Notes
///
/// Computationally intensive, likely only useful during testing.
pub fn verify_integrity(&self) -> std::result::Result<(), String> {
let num_root_nodes = self
.nodes
.iter()
.filter(|(_key, node)| node.parent_hash.is_none())
.count();
if num_root_nodes != 1 {
return Err(format!(
"Tree has {} roots, should have exactly one.",
num_root_nodes
));
}
let verify_node_exists = |key: Hash256, msg: String| -> std::result::Result<(), String> {
if self.nodes.contains_key(&key) {
Ok(())
} else {
Err(msg)
}
};
// Iterate through all the nodes and ensure all references they store are valid.
self.nodes
.iter()
.map(|(_key, node)| {
if let Some(parent_hash) = node.parent_hash {
verify_node_exists(parent_hash, "parent must exist".to_string())?;
}
node.children
.iter()
.map(|child| verify_node_exists(*child, "child_must_exist".to_string()))
.collect::<std::result::Result<(), String>>()?;
verify_node_exists(node.block_hash, "block hash must exist".to_string())?;
Ok(())
})
.collect::<std::result::Result<(), String>>()?;
Ok(())
}
fn get_node(&self, hash: Hash256) -> Result<&Node> {
self.nodes
.get(&hash)
@@ -595,6 +711,18 @@ impl Node {
Ok(())
}
pub fn remove_child(&mut self, child: Hash256) -> Result<()> {
let i = self
.children
.iter()
.position(|&c| c == child)
.ok_or_else(|| Error::MissingChild(child))?;
self.children.remove(i);
Ok(())
}
pub fn remove_voter(&mut self, voter: usize) -> Option<usize> {
let i = self.voters.iter().position(|&v| v == voter)?;
Some(self.voters.remove(i))