[Staking] Bounded Slashing: Paginated Offence Processing & Slash Application

polkadot/runtime/test-runtime/src/lib.rs

@@ -322,8 +322,8 @@ impl pallet_session::Config for Runtime {
 }
 
 impl pallet_session::historical::Config for Runtime {
-	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Runtime>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 pallet_staking_reward_curve::build! {

polkadot/runtime/westend/src/lib.rs

@@ -1871,6 +1871,7 @@ pub mod migrations {
 		parachains_shared::migration::MigrateToV1<Runtime>,
 		parachains_scheduler::migration::MigrateV2ToV3<Runtime>,
 		pallet_staking::migrations::v16::MigrateV15ToV16<Runtime>,
+		pallet_staking::migrations::v17::MigrateV16ToV17<Runtime>,
 		// permanent
 		pallet_xcm::migration::MigrateToLatestXcmVersion<Runtime>,
 	);

polkadot/runtime/westend/src/weights/pallet_staking.rs

@@ -805,4 +805,8 @@ impl<T: frame_system::Config> pallet_staking::WeightInfo for WeightInfo<T> {
 			.saturating_add(T::DbWeight::get().reads(6))
 			.saturating_add(T::DbWeight::get().writes(2))
 	}
+	fn apply_slash() -> Weight {
+		// TODO CI-FAIL: run CI bench bot
+		Weight::zero()
+	}
 }

prdoc/pr_7424.prdoc

@@ -0,0 +1,37 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: 'Bounded Slashing: Paginated Offence Processing & Slash Application'
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      This PR refactors the slashing mechanism in `pallet-staking` to be bounded by introducing paged offence processing and paged slash application.
+
+            ### Key Changes
+            - Offences are queued instead of being processed immediately.
+            - Slashes are computed in pages, stored as a `StorageDoubleMap` with `(Validator, SlashFraction, PageIndex)` to uniquely identify them.
+            - Slashes are applied incrementally across multiple blocks instead of a single unbounded operation.
+            - New storage items: `OffenceQueue`, `ProcessingOffence`, `OffenceQueueEras`.
+            - Updated API for cancelling and applying slashes.
+            - Preliminary benchmarks added; further optimizations planned.
+
+            This enables staking slashing to scale efficiently and removes a major blocker for staking migration to a parachain (AH).
+
+crates:
+- name: pallet-babe
+  bump: patch
+- name: pallet-staking
+  bump: major
+- name: pallet-grandpa
+  bump: patch
+- name: westend-runtime
+  bump: minor
+- name: pallet-beefy
+  bump: patch
+- name: pallet-offences-benchmarking
+  bump: patch
+- name: pallet-session-benchmarking
+  bump: patch
+- name: pallet-root-offences
+  bump: patch

substrate/bin/node/runtime/src/lib.rs

@@ -675,8 +675,6 @@ impl_opaque_keys! {
 
 #[cfg(feature = "staking-playground")]
 pub mod staking_playground {
-	use pallet_staking::Exposure;
-
 	use super::*;
 
 	/// An adapter to make the chain work with --dev only, even though it is running a large staking
@@ -711,61 +709,43 @@ pub mod staking_playground {
 		}
 	}
 
-	impl pallet_session::historical::SessionManager<AccountId, Exposure<AccountId, Balance>>
-		for AliceAsOnlyValidator
-	{
+	impl pallet_session::historical::SessionManager<AccountId, ()> for AliceAsOnlyValidator {
 		fn end_session(end_index: sp_staking::SessionIndex) {
-			<Staking as pallet_session::historical::SessionManager<
-				AccountId,
-				Exposure<AccountId, Balance>,
-			>>::end_session(end_index)
+			<Staking as pallet_session::historical::SessionManager<AccountId, ()>>::end_session(
+				end_index,
+			)
 		}
 
-		fn new_session(
-			new_index: sp_staking::SessionIndex,
-		) -> Option<Vec<(AccountId, Exposure<AccountId, Balance>)>> {
-			<Staking as pallet_session::historical::SessionManager<
-				AccountId,
-				Exposure<AccountId, Balance>,
-			>>::new_session(new_index)
+		fn new_session(new_index: sp_staking::SessionIndex) -> Option<Vec<(AccountId, ())>> {
+			<Staking as pallet_session::historical::SessionManager<AccountId, ()>>::new_session(
+				new_index,
+			)
 			.map(|_ignored| {
 				// construct a fake exposure for alice.
-				vec![(
-					sp_keyring::Sr25519Keyring::AliceStash.to_account_id().into(),
-					pallet_staking::Exposure {
-						total: 1_000_000_000,
-						own: 1_000_000_000,
-						others: vec![],
-					},
-				)]
+				vec![(sp_keyring::Sr25519Keyring::AliceStash.to_account_id().into(), ())]
 			})
 		}
 
 		fn new_session_genesis(
 			new_index: sp_staking::SessionIndex,
-		) -> Option<Vec<(AccountId, Exposure<AccountId, Balance>)>> {
+		) -> Option<Vec<(AccountId, ())>> {
 			<Staking as pallet_session::historical::SessionManager<
 				AccountId,
-				Exposure<AccountId, Balance>,
+				(),
 			>>::new_session_genesis(new_index)
 			.map(|_ignored| {
 				// construct a fake exposure for alice.
 				vec![(
 					sp_keyring::Sr25519Keyring::AliceStash.to_account_id().into(),
-					pallet_staking::Exposure {
-						total: 1_000_000_000,
-						own: 1_000_000_000,
-						others: vec![],
-					},
+					(),
 				)]
 			})
 		}
 
 		fn start_session(start_index: sp_staking::SessionIndex) {
-			<Staking as pallet_session::historical::SessionManager<
-				AccountId,
-				Exposure<AccountId, Balance>,
-			>>::start_session(start_index)
+			<Staking as pallet_session::historical::SessionManager<AccountId, ()>>::start_session(
+				start_index,
+			)
 		}
 	}
 }
@@ -789,8 +769,8 @@ impl pallet_session::Config for Runtime {
 }
 
 impl pallet_session::historical::Config for Runtime {
-	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Runtime>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 pallet_staking_reward_curve::build! {

substrate/frame/babe/src/mock.rs

@@ -104,8 +104,8 @@ impl pallet_session::Config for Test {
 }
 
 impl pallet_session::historical::Config for Test {
-	type FullIdentification = pallet_staking::Exposure<u64, u128>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Self>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 impl pallet_authorship::Config for Test {

substrate/frame/beefy/src/mock.rs

@@ -188,8 +188,8 @@ impl pallet_session::Config for Test {
 }
 
 impl pallet_session::historical::Config for Test {
-	type FullIdentification = pallet_staking::Exposure<u64, u128>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Self>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 impl pallet_authorship::Config for Test {

substrate/frame/election-provider-multi-phase/test-staking-e2e/src/mock.rs

@@ -145,8 +145,8 @@ impl pallet_session::Config for Runtime {
 	type WeightInfo = ();
 }
 impl pallet_session::historical::Config for Runtime {
-	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Runtime>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 frame_election_provider_support::generate_solution_type!(
@@ -908,10 +908,7 @@ pub(crate) fn on_offence_now(
 // Add offence to validator, slash it.
 pub(crate) fn add_slash(who: &AccountId) {
 	on_offence_now(
-		&[OffenceDetails {
-			offender: (*who, Staking::eras_stakers(active_era(), who)),
-			reporters: vec![],
-		}],
+		&[OffenceDetails { offender: (*who, ()), reporters: vec![] }],
 		&[Perbill::from_percent(10)],
 	);
 }

substrate/frame/grandpa/src/mock.rs

@@ -108,8 +108,8 @@ impl pallet_session::Config for Test {
 }
 
 impl pallet_session::historical::Config for Test {
-	type FullIdentification = pallet_staking::Exposure<u64, u128>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Self>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 impl pallet_authorship::Config for Test {

substrate/frame/offences/benchmarking/src/inner.rs

@@ -170,6 +170,13 @@ fn make_offenders<T: Config>(
 	Ok(id_tuples)
 }
 
+#[cfg(test)]
+fn run_staking_next_block<T: Config>() {
+	use frame_support::traits::Hooks;
+	System::<T>::set_block_number(System::<T>::block_number().saturating_add(1u32.into()));
+	Staking::<T>::on_initialize(System::<T>::block_number());
+}
+
 #[cfg(test)]
 fn assert_all_slashes_applied<T>(offender_count: usize)
 where
@@ -185,7 +192,7 @@ where
 	// (n nominators + one validator) * slashed + Slash Reported
 	assert_eq!(
 		System::<T>::read_events_for_pallet::<pallet_staking::Event<T>>().len(),
-		1 * (offender_count + 1) as usize + 1
+		1 * (offender_count + 1) as usize + 2
 	);
 	// offence
 	assert_eq!(System::<T>::read_events_for_pallet::<pallet_offences::Event>().len(), 1);
@@ -232,6 +239,8 @@ mod benchmarks {
 
 		#[cfg(test)]
 		{
+			// slashes applied at the next block.
+			run_staking_next_block::<T>();
 			assert_all_slashes_applied::<T>(n as usize);
 		}
 
@@ -266,6 +275,8 @@ mod benchmarks {
 		}
 		#[cfg(test)]
 		{
+			// slashes applied at the next block.
+			run_staking_next_block::<T>();
 			assert_all_slashes_applied::<T>(n as usize);
 		}
 

substrate/frame/offences/benchmarking/src/mock.rs

@@ -33,7 +33,6 @@ use sp_runtime::{
 };
 
 type AccountId = u64;
-type Balance = u64;
 
 #[derive_impl(frame_system::config_preludes::TestDefaultConfig)]
 impl frame_system::Config for Test {
@@ -54,8 +53,8 @@ impl pallet_timestamp::Config for Test {
 	type WeightInfo = ();
 }
 impl pallet_session::historical::Config for Test {
-	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Test>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 sp_runtime::impl_opaque_keys! {

substrate/frame/root-offences/src/lib.rs

@@ -31,7 +31,7 @@ extern crate alloc;
 
 use alloc::vec::Vec;
 use pallet_session::historical::IdentificationTuple;
-use pallet_staking::{BalanceOf, Exposure, ExposureOf, Pallet as Staking};
+use pallet_staking::Pallet as Staking;
 use sp_runtime::Perbill;
 use sp_staking::offence::OnOffenceHandler;
 
@@ -49,11 +49,8 @@ pub mod pallet {
 		+ pallet_staking::Config
 		+ pallet_session::Config<ValidatorId = <Self as frame_system::Config>::AccountId>
 		+ pallet_session::historical::Config<
-			FullIdentification = Exposure<
-				<Self as frame_system::Config>::AccountId,
-				BalanceOf<Self>,
-			>,
-			FullIdentificationOf = ExposureOf<Self>,
+			FullIdentification = (),
+			FullIdentificationOf = pallet_staking::NullIdentity,
 		>
 	{
 		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
@@ -106,15 +103,11 @@ pub mod pallet {
 		fn get_offence_details(
 			offenders: Vec<(T::AccountId, Perbill)>,
 		) -> Result<Vec<OffenceDetails<T>>, DispatchError> {
-			let now = pallet_staking::ActiveEra::<T>::get()
-				.map(|e| e.index)
-				.ok_or(Error::<T>::FailedToGetActiveEra)?;
-
 			Ok(offenders
 				.clone()
 				.into_iter()
 				.map(|(o, _)| OffenceDetails::<T> {
-					offender: (o.clone(), Staking::<T>::eras_stakers(now, &o)),
+					offender: (o.clone(), ()),
 					reporters: Default::default(),
 				})
 				.collect())
@@ -124,7 +117,7 @@ pub mod pallet {
 		fn submit_offence(offenders: &[OffenceDetails<T>], slash_fraction: &[Perbill]) {
 			let session_index = <pallet_session::Pallet<T> as frame_support::traits::ValidatorSet<T::AccountId>>::session_index();
 
-			<pallet_staking::Pallet<T> as OnOffenceHandler<
+			<Staking<T> as OnOffenceHandler<
 				T::AccountId,
 				IdentificationTuple<T>,
 				Weight,

substrate/frame/root-offences/src/mock.rs

@@ -28,7 +28,7 @@ use frame_support::{
 	traits::{ConstU32, ConstU64, OneSessionHandler},
 	BoundedVec,
 };
-use pallet_staking::StakerStatus;
+use pallet_staking::{BalanceOf, StakerStatus};
 use sp_core::ConstBool;
 use sp_runtime::{curve::PiecewiseLinear, testing::UintAuthorityId, traits::Zero, BuildStorage};
 use sp_staking::{EraIndex, SessionIndex};
@@ -148,8 +148,8 @@ impl pallet_staking::Config for Test {
 }
 
 impl pallet_session::historical::Config for Test {
-	type FullIdentification = pallet_staking::Exposure<AccountId, Balance>;
-	type FullIdentificationOf = pallet_staking::ExposureOf<Test>;
+	type FullIdentification = ();
+	type FullIdentificationOf = pallet_staking::NullIdentity;
 }
 
 sp_runtime::impl_opaque_keys! {
@@ -297,6 +297,11 @@ pub(crate) fn run_to_block(n: BlockNumber) {
 	);
 }
 
+/// Progress by n block.
+pub(crate) fn advance_blocks(n: u64) {
+	run_to_block(System::block_number() + n);
+}
+
 pub(crate) fn active_era() -> EraIndex {
 	pallet_staking::ActiveEra::<Test>::get().unwrap().index
 }

substrate/frame/root-offences/src/tests.rs

@@ -17,7 +17,10 @@
 
 use super::*;
 use frame_support::{assert_err, assert_ok};
-use mock::{active_era, start_session, ExtBuilder, RootOffences, RuntimeOrigin, System, Test as T};
+use mock::{
+	active_era, advance_blocks, start_session, ExtBuilder, RootOffences, RuntimeOrigin, System,
+	Test as T,
+};
 use pallet_staking::asset;
 
 #[test]
@@ -42,6 +45,10 @@ fn create_offence_works_given_root_origin() {
 		assert_ok!(RootOffences::create_offence(RuntimeOrigin::root(), offenders.clone()));
 
 		System::assert_last_event(Event::OffenceCreated { offenders }.into());
+
+		// offence is processed in the following block.
+		advance_blocks(1);
+
 		// the slash should be applied right away.
 		assert_eq!(asset::staked::<T>(&11), 500);
 
@@ -66,6 +73,9 @@ fn create_offence_wont_slash_non_active_validators() {
 
 		System::assert_last_event(Event::OffenceCreated { offenders }.into());
 
+		// advance to the next block so offence gets processed.
+		advance_blocks(1);
+
 		// so 31 didn't get slashed.
 		assert_eq!(asset::staked::<T>(&31), 500);