Fix session index lookup for activated leaf (#4850)

polkadot/node/network/availability-distribution/src/requester/mod.rs

@@ -33,7 +33,7 @@ use futures::{
 };
 
 use polkadot_node_subsystem_util::runtime::{get_occupied_cores, RuntimeInfo};
-use polkadot_primitives::v2::{CandidateHash, Hash, OccupiedCore};
+use polkadot_primitives::v2::{CandidateHash, Hash, OccupiedCore, SessionIndex};
 use polkadot_subsystem::{
 	messages::{AllMessages, ChainApiMessage},
 	ActivatedLeaf, ActiveLeavesUpdate, LeafStatus, SubsystemContext,
@@ -130,22 +130,13 @@ impl Requester {
 		Context: SubsystemContext,
 	{
 		let ActivatedLeaf { hash: leaf, .. } = new_head;
-		let ancestors_in_session = get_block_ancestors_in_same_session(
+		let (leaf_session_index, ancestors_in_session) = get_block_ancestors_in_same_session(
 			ctx,
 			runtime,
 			leaf,
 			Self::LEAF_ANCESTRY_LEN_WITHIN_SESSION,
 		)
-		.await
-		.unwrap_or_else(|err| {
-			tracing::debug!(
-				target: LOG_TARGET,
-				leaf = ?leaf,
-				"Failed to fetch leaf ancestors in the same session due to an error: {}",
-				err
-			);
-			Vec::new()
-		});
+		.await?;
 		// Also spawn or bump tasks for candidates in ancestry in the same session.
 		for hash in std::iter::once(leaf).chain(ancestors_in_session) {
 			let cores = get_occupied_cores(ctx, hash).await?;
@@ -161,7 +152,7 @@ impl Requester {
 			// The next time the subsystem receives leaf update, some of spawned task will be bumped
 			// to be live in fresh relay parent, while some might get dropped due to the current leaf
 			// being deactivated.
-			self.add_cores(ctx, runtime, leaf, cores).await?;
+			self.add_cores(ctx, runtime, leaf, leaf_session_index, cores).await?;
 		}
 
 		Ok(())
@@ -189,6 +180,7 @@ impl Requester {
 		ctx: &mut Context,
 		runtime: &mut RuntimeInfo,
 		leaf: Hash,
+		leaf_session_index: SessionIndex,
 		cores: impl IntoIterator<Item = OccupiedCore>,
 	) -> Result<()>
 	where
@@ -215,6 +207,7 @@ impl Requester {
 							// at session boundaries. At the same time, only leaves are guaranteed to
 							// be fetchable by the state trie.
 							leaf,
+							leaf_session_index,
 							|info| FetchTaskConfig::new(leaf, &core, tx, metrics, info),
 						)
 						.await
@@ -262,12 +255,14 @@ impl Stream for Requester {
 }
 
 /// Requests up to `limit` ancestor hashes of relay parent in the same session.
+///
+/// Also returns session index of the `head`.
 async fn get_block_ancestors_in_same_session<Context>(
 	ctx: &mut Context,
 	runtime: &mut RuntimeInfo,
 	head: Hash,
 	limit: usize,
-) -> Result<Vec<Hash>>
+) -> Result<(SessionIndex, Vec<Hash>)>
 where
 	Context: SubsystemContext,
 {
@@ -284,7 +279,7 @@ where
 		Some(parent) => runtime.get_session_index_for_child(ctx.sender(), *parent).await?,
 		None => {
 			// No first element, i.e. empty.
-			return Ok(ancestors)
+			return Ok((0, ancestors))
 		},
 	};
 
@@ -303,7 +298,7 @@ where
 	// Drop the rest.
 	ancestors.truncate(session_ancestry_len);
 
-	Ok(ancestors)
+	Ok((head_session_index, ancestors))
 }
 
 /// Request up to `limit` ancestor hashes of relay parent from the Chain API.

polkadot/node/network/availability-distribution/src/requester/session_cache.rs

@@ -99,14 +99,13 @@ impl SessionCache {
 		ctx: &mut Context,
 		runtime: &mut RuntimeInfo,
 		parent: Hash,
+		session_index: SessionIndex,
 		with_info: F,
 	) -> Result<Option<R>>
 	where
 		Context: SubsystemContext,
 		F: FnOnce(&SessionInfo) -> R,
 	{
-		let session_index = runtime.get_session_index_for_child(ctx.sender(), parent).await?;
-
 		if let Some(o_info) = self.session_info_cache.get(&session_index) {
 			tracing::trace!(target: LOG_TARGET, session_index, "Got session from lru");
 			return Ok(Some(with_info(o_info)))

polkadot/node/network/availability-distribution/src/tests/state.rs

@@ -45,7 +45,7 @@ use polkadot_primitives::v2::{
 };
 use polkadot_subsystem::{
 	messages::{
-		AllMessages, AvailabilityDistributionMessage, AvailabilityStoreMessage,
+		AllMessages, AvailabilityDistributionMessage, AvailabilityStoreMessage, ChainApiMessage,
 		NetworkBridgeMessage, RuntimeApiMessage, RuntimeApiRequest,
 	},
 	ActivatedLeaf, ActiveLeavesUpdate, FromOverseer, LeafStatus, OverseerSignal,
@@ -278,6 +278,14 @@ impl TestState {
 						},
 					}
 				},
+				AllMessages::ChainApi(ChainApiMessage::Ancestors { hash, k, response_channel }) => {
+					let chain = &self.relay_chain;
+					let maybe_block_position = chain.iter().position(|h| *h == hash);
+					let ancestors = maybe_block_position
+						.map(|idx| chain[..idx].iter().rev().take(k).copied().collect())
+						.unwrap_or_default();
+					response_channel.send(Ok(ancestors)).expect("Receiver is expected to be alive");
+				},
 				_ => {},
 			}
 		}