[Runtime] Bound XCMP queue (#2302)

Remove `without_storage_info` from the XCMP queue pallet. Part of
#323

Changes:
- Limit the number of channels that can be suspended at the same time.
- Limit the number of channels that can have messages or signals pending
at the same time.

A No-OP migration is put in place to ensure that all `BoundedVec`s still
decode and not truncate after upgrade. The storage version is thereby
bumped to 4 to have our tooling remind us to deploy that migration.

---------

Signed-off-by: Oliver Tale-Yazdi <[email protected]>
Co-authored-by: Francisco Aguirre <[email protected]>

cumulus/pallets/parachain-system/src/lib.rs

@@ -30,7 +30,7 @@
 use codec::{Decode, Encode};
 use cumulus_primitives_core::{
 	relay_chain, AbridgedHostConfiguration, ChannelInfo, ChannelStatus, CollationInfo,
-	GetChannelInfo, InboundDownwardMessage, InboundHrmpMessage, MessageSendError,
+	GetChannelInfo, InboundDownwardMessage, InboundHrmpMessage, ListChannelInfos, MessageSendError,
 	OutboundHrmpMessage, ParaId, PersistedValidationData, UpwardMessage, UpwardMessageSender,
 	XcmpMessageHandler, XcmpMessageSource,
 };
@@ -1023,6 +1023,13 @@ impl<T: Config> FeeTracker for Pallet<T> {
 	}
 }
 
+impl<T: Config> ListChannelInfos for Pallet<T> {
+	fn outgoing_channels() -> Vec<ParaId> {
+		let Some(state) = Self::relevant_messaging_state() else { return Vec::new() };
+		state.egress_channels.into_iter().map(|(id, _)| id).collect()
+	}
+}
+
 impl<T: Config> GetChannelInfo for Pallet<T> {
 	fn get_channel_status(id: ParaId) -> ChannelStatus {
 		// Note, that we are using `relevant_messaging_state` which may be from the previous

cumulus/pallets/xcmp-queue/src/lib.rs

@@ -51,7 +51,7 @@ pub mod weights;
 pub use weights::WeightInfo;
 
 use bounded_collections::BoundedBTreeSet;
-use codec::{Decode, DecodeLimit, Encode};
+use codec::{Decode, DecodeLimit, Encode, MaxEncodedLen};
 use cumulus_primitives_core::{
 	relay_chain::BlockNumber as RelayBlockNumber, ChannelStatus, GetChannelInfo, MessageSendError,
 	ParaId, XcmpMessageFormat, XcmpMessageHandler, XcmpMessageSource,
@@ -105,7 +105,6 @@ pub mod pallet {
 
 	#[pallet::pallet]
 	#[pallet::storage_version(migration::STORAGE_VERSION)]
-	#[pallet::without_storage_info]
 	pub struct Pallet<T>(_);
 
 	#[pallet::config]
@@ -132,6 +131,25 @@ pub mod pallet {
 		#[pallet::constant]
 		type MaxInboundSuspended: Get<u32>;
 
+		/// Maximal number of outbound XCMP channels that can have messages queued at the same time.
+		///
+		/// If this is reached, then no further messages can be sent to channels that do not yet
+		/// have a message queued. This should be set to the expected maximum of outbound channels
+		/// which is determined by [`Self::ChannelInfo`]. It is important to set this correctly,
+		/// since otherwise the congestion control protocol will not work as intended and messages
+		/// may be dropped. This value increases the PoV and should therefore not be picked too
+		/// high.
+		#[pallet::constant]
+		type MaxActiveOutboundChannels: Get<u32>;
+
+		/// The maximal page size for HRMP message pages.
+		///
+		/// A lower limit can be set dynamically, but this is the hard-limit for the PoV worst case
+		/// benchmarking. The limit for the size of a message is slightly below this, since some
+		/// overhead is incurred for encoding the format.
+		#[pallet::constant]
+		type MaxPageSize: Get<u32>;
+
 		/// The origin that is allowed to resume or suspend the XCMP queue.
 		type ControllerOrigin: EnsureOrigin<Self::RuntimeOrigin>;
 
@@ -276,6 +294,10 @@ pub mod pallet {
 		AlreadySuspended,
 		/// The execution is already resumed.
 		AlreadyResumed,
+		/// There are too many active outbound channels.
+		TooManyOutboundChannels,
+		/// The message is too big.
+		TooBig,
 	}
 
 	/// The suspended inbound XCMP channels. All others are not suspended.
@@ -297,19 +319,28 @@ pub mod pallet {
 	/// case of the need to send a high-priority signal message this block.
 	/// The bool is true if there is a signal message waiting to be sent.
 	#[pallet::storage]
-	pub(super) type OutboundXcmpStatus<T: Config> =
-		StorageValue<_, Vec<OutboundChannelDetails>, ValueQuery>;
+	pub(super) type OutboundXcmpStatus<T: Config> = StorageValue<
+		_,
+		BoundedVec<OutboundChannelDetails, T::MaxActiveOutboundChannels>,
+		ValueQuery,
+	>;
 
-	// The new way of doing it:
 	/// The messages outbound in a given XCMP channel.
 	#[pallet::storage]
-	pub(super) type OutboundXcmpMessages<T: Config> =
-		StorageDoubleMap<_, Blake2_128Concat, ParaId, Twox64Concat, u16, Vec<u8>, ValueQuery>;
+	pub(super) type OutboundXcmpMessages<T: Config> = StorageDoubleMap<
+		_,
+		Blake2_128Concat,
+		ParaId,
+		Twox64Concat,
+		u16,
+		BoundedVec<u8, T::MaxPageSize>,
+		ValueQuery,
+	>;
 
 	/// Any signal messages waiting to be sent.
 	#[pallet::storage]
 	pub(super) type SignalMessages<T: Config> =
-		StorageMap<_, Blake2_128Concat, ParaId, Vec<u8>, ValueQuery>;
+		StorageMap<_, Blake2_128Concat, ParaId, BoundedVec<u8, T::MaxPageSize>, ValueQuery>;
 
 	/// The configuration which controls the dynamics of the outbound queue.
 	#[pallet::storage]
@@ -331,15 +362,14 @@ pub mod pallet {
 		StorageMap<_, Twox64Concat, ParaId, FixedU128, ValueQuery, InitialFactor>;
 }
 
-#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, RuntimeDebug, TypeInfo)]
+#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, RuntimeDebug, TypeInfo, MaxEncodedLen)]
 pub enum OutboundState {
 	Ok,
 	Suspended,
 }
 
 /// Struct containing detailed information about the outbound channel.
-#[derive(Clone, Eq, PartialEq, Encode, Decode, TypeInfo)]
-#[cfg_attr(feature = "std", derive(Debug))]
+#[derive(Clone, Eq, PartialEq, Encode, Decode, TypeInfo, RuntimeDebug, MaxEncodedLen)]
 pub struct OutboundChannelDetails {
 	/// The `ParaId` of the parachain that this channel is connected with.
 	recipient: ParaId,
@@ -375,7 +405,7 @@ impl OutboundChannelDetails {
 	}
 }
 
-#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, RuntimeDebug, TypeInfo)]
+#[derive(Copy, Clone, Eq, PartialEq, Encode, Decode, RuntimeDebug, TypeInfo, MaxEncodedLen)]
 pub struct QueueConfigData {
 	/// The number of pages which must be in the queue for the other side to be told to suspend
 	/// their sending.
@@ -478,7 +508,9 @@ impl<T: Config> Pallet<T> {
 		{
 			details
 		} else {
-			all_channels.push(OutboundChannelDetails::new(recipient));
+			all_channels
+				.try_push(OutboundChannelDetails::new(recipient))
+				.map_err(|_| MessageSendError::TooManyChannels)?;
 			all_channels
 				.last_mut()
 				.expect("can't be empty; a new element was just pushed; qed")
@@ -503,7 +535,7 @@ impl<T: Config> Pallet<T> {
 						if page.len() + encoded_fragment.len() > max_message_size {
 							return None
 						}
-						page.extend_from_slice(&encoded_fragment[..]);
+						page.try_extend(encoded_fragment.iter().cloned()).ok()?;
 						Some(page.len())
 					},
 				)
@@ -521,7 +553,9 @@ impl<T: Config> Pallet<T> {
 			new_page.extend_from_slice(&encoded_fragment[..]);
 			let last_page_size = new_page.len();
 			let number_of_pages = (channel_details.last_index - channel_details.first_index) as u32;
-			<OutboundXcmpMessages<T>>::insert(recipient, page_index, new_page);
+			let bounded_page =
+				BoundedVec::try_from(new_page).map_err(|_| MessageSendError::TooBig)?;
+			<OutboundXcmpMessages<T>>::insert(recipient, page_index, bounded_page);
 			<OutboundXcmpStatus<T>>::put(all_channels);
 			(number_of_pages, last_page_size)
 		};
@@ -543,17 +577,21 @@ impl<T: Config> Pallet<T> {
 
 	/// Sends a signal to the `dest` chain over XCMP. This is guaranteed to be dispatched on this
 	/// block.
-	fn send_signal(dest: ParaId, signal: ChannelSignal) {
+	fn send_signal(dest: ParaId, signal: ChannelSignal) -> Result<(), Error<T>> {
 		let mut s = <OutboundXcmpStatus<T>>::get();
 		if let Some(details) = s.iter_mut().find(|item| item.recipient == dest) {
 			details.signals_exist = true;
 		} else {
-			s.push(OutboundChannelDetails::new(dest).with_signals());
+			s.try_push(OutboundChannelDetails::new(dest).with_signals())
+				.map_err(|_| Error::<T>::TooManyOutboundChannels)?;
 		}
-		<SignalMessages<T>>::mutate(dest, |page| {
-			*page = (XcmpMessageFormat::Signals, signal).encode();
-		});
+
+		let page = BoundedVec::try_from((XcmpMessageFormat::Signals, signal).encode())
+			.map_err(|_| Error::<T>::TooBig)?;
+
+		<SignalMessages<T>>::insert(dest, page);
 		<OutboundXcmpStatus<T>>::put(s);
+		Ok(())
 	}
 
 	fn suspend_channel(target: ParaId) {
@@ -563,7 +601,13 @@ impl<T: Config> Pallet<T> {
 				defensive_assert!(ok, "WARNING: Attempt to suspend channel that was not Ok.");
 				details.state = OutboundState::Suspended;
 			} else {
-				s.push(OutboundChannelDetails::new(target).with_suspended_state());
+				if s.try_push(OutboundChannelDetails::new(target).with_suspended_state()).is_err() {
+					// Nothing that we can do here. The outbound channel does not exist either, so
+					// there should be no message going out as well. The next time that the channel
+					// can be created it will again get the suspension from the remote side. It can
+					// therefore result in a few lost messages, but should eventually self-repair.
+					defensive!("Cannot pause channel; too many outbound channels");
+				}
 			}
 		});
 	}
@@ -664,13 +708,17 @@ impl<T: Config> OnQueueChanged<ParaId> for Pallet<T> {
 		let suspended = suspended_channels.contains(&para);
 
 		if suspended && fp.pages <= resume_threshold {
-			Self::send_signal(para, ChannelSignal::Resume);
+			// If the resuming fails then it is not critical. We will retry in the future.
+			let _ = Self::send_signal(para, ChannelSignal::Resume);
 
 			suspended_channels.remove(&para);
 			<InboundXcmpSuspended<T>>::put(suspended_channels);
 		} else if !suspended && fp.pages >= suspend_threshold {
 			log::warn!("XCMP queue for sibling {:?} is full; suspending channel.", para);
-			Self::send_signal(para, ChannelSignal::Suspend);
+			if let Err(_) = Self::send_signal(para, ChannelSignal::Suspend) {
+				// It will retry if `drop_threshold` is not reached, but it could be too late.
+				defensive!("Could not send suspension signal; future messages may be dropped.");
+			}
 
 			if let Err(err) = suspended_channels.try_insert(para) {
 				log::error!("Too many channels suspended; cannot suspend sibling {:?}: {:?}; further messages may be dropped.", para, err);
@@ -842,7 +890,7 @@ impl<T: Config> XcmpMessageSource for Pallet<T> {
 				//   since it's so unlikely then for now we just drop it.
 				defensive!("WARNING: oversize message in queue - dropping");
 			} else {
-				result.push((para_id, page));
+				result.push((para_id, page.into_inner()));
 			}
 
 			let max_total_size = match T::ChannelInfo::get_channel_info(para_id) {
@@ -890,7 +938,14 @@ impl<T: Config> XcmpMessageSource for Pallet<T> {
 		let pruned = old_statuses_len - statuses.len();
 		// removing an item from status implies a message being sent, so the result messages must
 		// be no less than the pruned channels.
-		statuses.rotate_left(result.len().saturating_sub(pruned));
+
+		// TODO <https://github.com/paritytech/parity-common/pull/800>
+		{
+			let mut statuses_inner = statuses.into_inner();
+			statuses_inner.rotate_left(result.len().saturating_sub(pruned));
+			statuses = BoundedVec::try_from(statuses_inner)
+				.expect("Rotating does not change the length; it still fits; qed");
+		}
 
 		<OutboundXcmpStatus<T>>::put(statuses);
 

cumulus/pallets/xcmp-queue/src/migration.rs

@@ -16,6 +16,8 @@
 
 //! A module that is responsible for migration of storage.
 
+pub mod v5;
+
 use crate::{Config, OverweightIndex, Pallet, QueueConfig, QueueConfigData, DEFAULT_POV_SIZE};
 use cumulus_primitives_core::XcmpMessageFormat;
 use frame_support::{
@@ -25,7 +27,7 @@ use frame_support::{
 };
 
 /// The current storage version.
-pub const STORAGE_VERSION: StorageVersion = StorageVersion::new(4);
+pub const STORAGE_VERSION: StorageVersion = StorageVersion::new(5);
 
 pub const LOG: &str = "runtime::xcmp-queue-migration";
 
@@ -264,9 +266,9 @@ pub mod v4 {
 
 	/// Migrates `QueueConfigData` to v4, removing deprecated fields and bumping page
 	/// thresholds to at least the default values.
-	pub struct UncheckedMigrationToV4<T: Config>(PhantomData<T>);
+	pub struct UncheckedMigrateV3ToV4<T: Config>(PhantomData<T>);
 
-	impl<T: Config> OnRuntimeUpgrade for UncheckedMigrationToV4<T> {
+	impl<T: Config> OnRuntimeUpgrade for UncheckedMigrateV3ToV4<T> {
 		fn on_runtime_upgrade() -> Weight {
 			let translate = |pre: v2::QueueConfigData| -> QueueConfigData {
 				let pre_default = v2::QueueConfigData::default();
@@ -299,13 +301,13 @@ pub mod v4 {
 		}
 	}
 
-	/// [`UncheckedMigrationToV4`] wrapped in a
+	/// [`UncheckedMigrateV3ToV4`] wrapped in a
 	/// [`VersionedMigration`](frame_support::migrations::VersionedMigration), ensuring the
 	/// migration is only performed when on-chain version is 3.
-	pub type MigrationToV4<T> = frame_support::migrations::VersionedMigration<
+	pub type MigrateV3ToV4<T> = frame_support::migrations::VersionedMigration<
 		3,
 		4,
-		UncheckedMigrationToV4<T>,
+		UncheckedMigrateV3ToV4<T>,
 		Pallet<T>,
 		<T as frame_system::Config>::DbWeight,
 	>;
@@ -372,10 +374,10 @@ mod tests {
 				&v2.encode(),
 			);
 
-			let bytes = v4::MigrationToV4::<Test>::pre_upgrade();
+			let bytes = v4::MigrateV3ToV4::<Test>::pre_upgrade();
 			assert!(bytes.is_ok());
-			v4::MigrationToV4::<Test>::on_runtime_upgrade();
-			assert!(v4::MigrationToV4::<Test>::post_upgrade(bytes.unwrap()).is_ok());
+			v4::MigrateV3ToV4::<Test>::on_runtime_upgrade();
+			assert!(v4::MigrateV3ToV4::<Test>::post_upgrade(bytes.unwrap()).is_ok());
 
 			let v4 = QueueConfig::<Test>::get();
 
@@ -401,10 +403,10 @@ mod tests {
 				&v2.encode(),
 			);
 
-			let bytes = v4::MigrationToV4::<Test>::pre_upgrade();
+			let bytes = v4::MigrateV3ToV4::<Test>::pre_upgrade();
 			assert!(bytes.is_ok());
-			v4::MigrationToV4::<Test>::on_runtime_upgrade();
-			assert!(v4::MigrationToV4::<Test>::post_upgrade(bytes.unwrap()).is_ok());
+			v4::MigrateV3ToV4::<Test>::on_runtime_upgrade();
+			assert!(v4::MigrateV3ToV4::<Test>::post_upgrade(bytes.unwrap()).is_ok());
 
 			let v4 = QueueConfig::<Test>::get();