Handling of disabled validators in backing subsystem (#1259)

Handles validator disabling in the backing subsystem. The PR introduces
two changes:
1. Don't import statements from disabled validators.
2. Don't validate and second if the local validator is disabled.

The purpose of this change is first to ignore statements from disabled
validators on the node side. This is an optimisation as these statements
are supposed to be cleared in the runtime too (still not implemented at
the moment). Additionally if the local node is a validator which is
disabled - don't process any new candidates.

---------

Co-authored-by: ordian <noreply@reusable.software>
Co-authored-by: ordian <write@reusable.software>

polkadot/node/core/backing/src/lib.rs

@@ -118,6 +118,7 @@ use statement_table::{
 	},
 	Config as TableConfig, Context as TableContextTrait, Table,
 };
+use util::vstaging::get_disabled_validators_with_fallback;
 
 mod error;
 
@@ -383,6 +384,21 @@ struct TableContext {
 	validator: Option<Validator>,
 	groups: HashMap<ParaId, Vec<ValidatorIndex>>,
 	validators: Vec<ValidatorId>,
+	disabled_validators: Vec<ValidatorIndex>,
+}
+
+impl TableContext {
+	// Returns `true` if the provided `ValidatorIndex` is in the disabled validators list
+	pub fn validator_is_disabled(&self, validator_idx: &ValidatorIndex) -> bool {
+		self.disabled_validators
+			.iter()
+			.any(|disabled_val_idx| *disabled_val_idx == *validator_idx)
+	}
+
+	// Returns `true` if the local validator is in the disabled validators list
+	pub fn local_validator_is_disabled(&self) -> Option<bool> {
+		self.validator.as_ref().map(|v| v.disabled())
+	}
 }
 
 impl TableContextTrait for TableContext {
@@ -1010,21 +1026,33 @@ async fn construct_per_relay_parent_state<Context>(
 	let minimum_backing_votes =
 		try_runtime_api!(request_min_backing_votes(parent, session_index, ctx.sender()).await);
 
+	// TODO: https://github.com/paritytech/polkadot-sdk/issues/1940
+	// Once runtime ver `DISABLED_VALIDATORS_RUNTIME_REQUIREMENT` is released remove this call to
+	// `get_disabled_validators_with_fallback`, add `request_disabled_validators` call to the
+	// `try_join!` above and use `try_runtime_api!` to get `disabled_validators`
+	let disabled_validators = get_disabled_validators_with_fallback(ctx.sender(), parent)
+		.await
+		.map_err(Error::UtilError)?;
+
 	let signing_context = SigningContext { parent_hash: parent, session_index };
-	let validator =
-		match Validator::construct(&validators, signing_context.clone(), keystore.clone()) {
-			Ok(v) => Some(v),
-			Err(util::Error::NotAValidator) => None,
-			Err(e) => {
-				gum::warn!(
-					target: LOG_TARGET,
-					err = ?e,
-					"Cannot participate in candidate backing",
-				);
+	let validator = match Validator::construct(
+		&validators,
+		&disabled_validators,
+		signing_context.clone(),
+		keystore.clone(),
+	) {
+		Ok(v) => Some(v),
+		Err(util::Error::NotAValidator) => None,
+		Err(e) => {
+			gum::warn!(
+				target: LOG_TARGET,
+				err = ?e,
+				"Cannot participate in candidate backing",
+			);
 
-				return Ok(None)
-			},
-		};
+			return Ok(None)
+		},
+	};
 
 	let mut groups = HashMap::new();
 	let n_cores = cores.len();
@@ -1054,7 +1082,7 @@ async fn construct_per_relay_parent_state<Context>(
 		}
 	}
 
-	let table_context = TableContext { groups, validators, validator };
+	let table_context = TableContext { validator, groups, validators, disabled_validators };
 	let table_config = TableConfig {
 		allow_multiple_seconded: match mode {
 			ProspectiveParachainsMode::Enabled { .. } => true,
@@ -1728,6 +1756,19 @@ async fn kick_off_validation_work<Context>(
 	background_validation_tx: &mpsc::Sender<(Hash, ValidatedCandidateCommand)>,
 	attesting: AttestingData,
 ) -> Result<(), Error> {
+	// Do nothing if the local validator is disabled or not a validator at all
+	match rp_state.table_context.local_validator_is_disabled() {
+		Some(true) => {
+			gum::info!(target: LOG_TARGET, "We are disabled - don't kick off validation");
+			return Ok(())
+		},
+		Some(false) => {}, // we are not disabled - move on
+		None => {
+			gum::debug!(target: LOG_TARGET, "We are not a validator - don't kick off validation");
+			return Ok(())
+		},
+	}
+
 	let candidate_hash = attesting.candidate.hash();
 	if rp_state.issued_statements.contains(&candidate_hash) {
 		return Ok(())
@@ -1785,6 +1826,16 @@ async fn maybe_validate_and_import<Context>(
 		},
 	};
 
+	// Don't import statement if the sender is disabled
+	if rp_state.table_context.validator_is_disabled(&statement.validator_index()) {
+		gum::debug!(
+			target: LOG_TARGET,
+			sender_validator_idx = ?statement.validator_index(),
+			"Not importing statement because the sender is disabled"
+		);
+		return Ok(())
+	}
+
 	let res = import_statement(ctx, rp_state, &mut state.per_candidate, &statement).await;
 
 	// if we get an Error::RejectedByProspectiveParachains,
@@ -1946,6 +1997,13 @@ async fn handle_second_message<Context>(
 		Some(r) => r,
 	};
 
+	// Just return if the local validator is disabled. If we are here the local node should be a
+	// validator but defensively use `unwrap_or(false)` to continue processing in this case.
+	if rp_state.table_context.local_validator_is_disabled().unwrap_or(false) {
+		gum::warn!(target: LOG_TARGET, "Local validator is disabled. Don't validate and second");
+		return Ok(())
+	}
+
 	// Sanity check that candidate is from our assignment.
 	if Some(candidate.descriptor().para_id) != rp_state.assignment {
 		gum::debug!(
@@ -1992,6 +2050,7 @@ async fn handle_statement_message<Context>(
 ) -> Result<(), Error> {
 	let _timer = metrics.time_process_statement();
 
+	// Validator disabling is handled in `maybe_validate_and_import`
 	match maybe_validate_and_import(ctx, state, relay_parent, statement).await {
 		Err(Error::ValidationFailed(_)) => Ok(()),
 		Err(e) => Err(e),