Issue RevertBlocks as soon as a dispute has `byzantine threshold + …

…1` invalid votes.

node/core/dispute-coordinator/src/import.rs

@@ -477,6 +477,35 @@ impl ImportResult {
 		self.is_freshly_concluded_against() || self.is_freshly_concluded_for()
 	}
 
+	// Returns the number of invalid own votes from the state provided. This function is a helper for
+	// `has_fresh_byzantine_threshold_against`
+	fn get_own_invalid_votes<T>(state: &CandidateVoteState<T>) -> usize {
+		state
+			.own_votes()
+			.map(|votes| {
+				votes.iter().fold(0, |acc, (_, (vote, _))| match vote {
+					DisputeStatement::Invalid(_) => acc + 1,
+					_ => acc,
+				})
+			})
+			.unwrap_or(0)
+	}
+
+	/// Whether or not the invalid vote count for the dispute went beyond the byzantine threshold
+	/// after the last import
+	pub fn has_fresh_byzantine_threshold_against(&self, byzantine_threshold: usize) -> bool {
+		// Total number of imported invalid votes + our own invalid votes
+		let imported_invalid_votes =
+			self.imported_invalid_votes() as usize + Self::get_own_invalid_votes(self.new_state());
+		// The number of invalid votes + our own invalid votes before the import
+		let old_invalid_votes = (self.imported_invalid_votes() as usize)
+			.saturating_sub(self.new_invalid_voters().len()) +
+			Self::get_own_invalid_votes(self.old_state());
+
+		old_invalid_votes as usize <= byzantine_threshold &&
+			imported_invalid_votes as usize > byzantine_threshold
+	}
+
 	/// Modify this `ImportResult`s, by importing additional approval votes.
 	///
 	/// Both results and `new_state` will be changed as if those approval votes had been in the

node/core/dispute-coordinator/src/initialized.rs

@@ -41,9 +41,9 @@ use polkadot_node_subsystem::{
 };
 use polkadot_node_subsystem_util::runtime::RuntimeInfo;
 use polkadot_primitives::{
-	BlockNumber, CandidateHash, CandidateReceipt, CompactStatement, DisputeStatement,
-	DisputeStatementSet, Hash, ScrapedOnChainVotes, SessionIndex, ValidDisputeStatementKind,
-	ValidatorId, ValidatorIndex,
+	byzantine_threshold, BlockNumber, CandidateHash, CandidateReceipt, CompactStatement,
+	DisputeStatement, DisputeStatementSet, Hash, ScrapedOnChainVotes, SessionIndex,
+	ValidDisputeStatementKind, ValidatorId, ValidatorIndex,
 };
 
 use crate::{
@@ -1094,7 +1094,9 @@ impl Initialized {
 
 		// Notify ChainSelection if a dispute has concluded against a candidate. ChainSelection
 		// will need to mark the candidate's relay parent as reverted.
-		if import_result.is_freshly_concluded_against() {
+		if import_result
+			.has_fresh_byzantine_threshold_against(byzantine_threshold(env.validators().len()))
+		{
 			let blocks_including = self.scraper.get_blocks_including_candidate(&candidate_hash);
 			for (parent_block_number, parent_block_hash) in &blocks_including {
 				gum::trace!(

node/core/dispute-coordinator/src/tests.rs

@@ -3284,8 +3284,8 @@ fn informs_chain_selection_when_dispute_concluded_against() {
 				)
 				.await;
 
-			let supermajority_threshold =
-				polkadot_primitives::supermajority_threshold(test_state.validators.len());
+			let byzantine_threshold =
+				polkadot_primitives::byzantine_threshold(test_state.validators.len());
 
 			let (valid_vote, invalid_vote) = generate_opposing_votes_pair(
 				&test_state,
@@ -3326,8 +3326,8 @@ fn informs_chain_selection_when_dispute_concluded_against() {
 			.await;
 
 			let mut statements = Vec::new();
-			// minus 2, because of local vote and one previously imported invalid vote.
-			for i in (0_u32..supermajority_threshold as u32 - 2).map(|i| i + 3) {
+			// own vote + `byzantine_threshold` more votes should be enough to issue `RevertBlocks`
+			for i in (0_u32..byzantine_threshold as u32).map(|i| i + 3) {
 				let vote = test_state.issue_explicit_statement_with_index(
 					ValidatorIndex(i),
 					candidate_hash,
@@ -3348,8 +3348,6 @@ fn informs_chain_selection_when_dispute_concluded_against() {
 					},
 				})
 				.await;
-			handle_approval_vote_request(&mut virtual_overseer, &candidate_hash, HashMap::new())
-				.await;
 
 			// Checking that concluded dispute has signaled the reversion of all parent blocks.
 			assert_matches!(
@@ -3363,6 +3361,9 @@ fn informs_chain_selection_when_dispute_concluded_against() {
 				"Overseer did not receive `ChainSelectionMessage::RevertBlocks` message"
 			);
 
+			// handle_approval_vote_request(&mut virtual_overseer, &candidate_hash, HashMap::new())
+			// 	.await;
+
 			// Wrap up
 			virtual_overseer.send(FromOrchestra::Signal(OverseerSignal::Conclude)).await;
 			assert_matches!(