Properly defer slashes (paritytech#11823)

* initial draft of fixing slashing

* fix test

* Update frame/staking/src/tests.rs

Co-authored-by: Piotr Mikołajczyk <piomiko41@gmail.com>

* last touches

* add more detail about unbonding

* add migration

* fmt

Co-authored-by: Piotr Mikołajczyk <piomiko41@gmail.com>
Co-authored-by: parity-processbot <>

frame/staking/src/lib.rs

@@ -872,11 +872,12 @@ enum Releases {
  V2_0_0,
  V3_0_0,
  V4_0_0,
- V5_0_0, // blockable validators.
- V6_0_0, // removal of all storage associated with offchain phragmen.
- V7_0_0, // keep track of number of nominators / validators in map
- V8_0_0, // populate `VoterList`.
- V9_0_0, // inject validators into `VoterList` as well.
+ V5_0_0, // blockable validators.
+ V6_0_0, // removal of all storage associated with offchain phragmen.
+ V7_0_0, // keep track of number of nominators / validators in map
+ V8_0_0, // populate `VoterList`.
+ V9_0_0, // inject validators into `VoterList` as well.
+ V10_0_0, // remove `EarliestUnappliedSlash`.
 }
 
 impl Default for Releases {

frame/staking/src/migrations.rs

@@ -20,6 +20,29 @@ use super::*;
 use frame_election_provider_support::SortedListProvider;
 use frame_support::traits::OnRuntimeUpgrade;
 
+pub mod v10 {
+ use super::*;
+ use frame_support::storage_alias;
+
+ #[storage_alias]
+ type EarliestUnappliedSlash<T: Config> = StorageValue<Pallet<T>, EraIndex>;
+
+ pub struct MigrateToV10<T>(sp_std::marker::PhantomData<T>);
+ impl<T: Config> OnRuntimeUpgrade for MigrateToV10<T> {
+ fn on_runtime_upgrade() -> frame_support::weights::Weight {
+ if StorageVersion::<T>::get() == Releases::V9_0_0 {
+ EarliestUnappliedSlash::<T>::kill();
+ StorageVersion::<T>::put(Releases::V10_0_0);
+
+ T::DbWeight::get().reads_writes(1, 1)
+ } else {
+ log!(warn, "MigrateToV10 should be removed.");
+ T::DbWeight::get().reads(1)
+ }
+ }
+ }
+}
+
 pub mod v9 {
  use super::*;
 

frame/staking/src/mock.rs

@@ -549,6 +549,7 @@ impl ExtBuilder {
  ext
  }
  pub fn build_and_execute(self, test: impl FnOnce() -> ()) {
+ sp_tracing::try_init_simple();
  let mut ext = self.build();
  ext.execute_with(test);
  ext.execute_with(post_conditions);
@@ -884,6 +885,20 @@ pub(crate) fn staking_events() -> Vec<crate::Event<Test>> {
  .collect()
 }
 
+parameter_types! {
+ static StakingEventsIndex: usize = 0;
+}
+
+pub(crate) fn staking_events_since_last_call() -> Vec<crate::Event<Test>> {
+ let all: Vec<_> = System::events()
+ .into_iter()
+ .filter_map(|r| if let Event::Staking(inner) = r.event { Some(inner) } else { None })
+ .collect();
+ let seen = StakingEventsIndex::get();
+ StakingEventsIndex::set(all.len());
+ all.into_iter().skip(seen).collect()
+}
+
 pub(crate) fn balances(who: &AccountId) -> (Balance, Balance) {
  (Balances::free_balance(who), Balances::reserved_balance(who))
 }

frame/staking/src/pallet/impls.rs

@@ -32,7 +32,7 @@ use frame_support::{
 use frame_system::{pallet_prelude::BlockNumberFor, RawOrigin};
 use pallet_session::historical;
 use sp_runtime::{
- traits::{Bounded, Convert, SaturatedConversion, Saturating, StaticLookup, Zero},
+ traits::{Bounded, Convert, One, SaturatedConversion, Saturating, StaticLookup, Zero},
  Perbill,
 };
 use sp_staking::{
@@ -599,20 +599,17 @@ impl<T: Config> Pallet<T> {
 
  /// Apply previously-unapplied slashes on the beginning of a new era, after a delay.
  fn apply_unapplied_slashes(active_era: EraIndex) {
- let slash_defer_duration = T::SlashDeferDuration::get();
- <Self as Store>::EarliestUnappliedSlash::mutate(|earliest| {
- if let Some(ref mut earliest) = earliest {
- let keep_from = active_era.saturating_sub(slash_defer_duration);
- for era in (*earliest)..keep_from {
- let era_slashes = <Self as Store>::UnappliedSlashes::take(&era);
- for slash in era_slashes {
- slashing::apply_slash::<T>(slash, era);
- }
- }
-
- *earliest = (*earliest).max(keep_from)
- }
- })
+ let era_slashes = <Self as Store>::UnappliedSlashes::take(&active_era);
+ log!(
+ debug,
+ "found {} slashes scheduled to be executed in era {:?}",
+ era_slashes.len(),
+ active_era,
+ );
+ for slash in era_slashes {
+ let slash_era = active_era.saturating_sub(T::SlashDeferDuration::get());
+ slashing::apply_slash::<T>(slash, slash_era);
+ }
  }
 
  /// Add reward points to validators using their stash account ID.
@@ -1209,11 +1206,6 @@ where
  }
  };
 
- <Self as Store>::EarliestUnappliedSlash::mutate(|earliest| {
- if earliest.is_none() {
- *earliest = Some(active_era)
- }
- });
  add_db_reads_writes(1, 1);
 
  let slash_defer_duration = T::SlashDeferDuration::get();
@@ -1263,9 +1255,18 @@ where
  }
  } else {
  // Defer to end of some `slash_defer_duration` from now.
- <Self as Store>::UnappliedSlashes::mutate(active_era, move |for_later| {
- for_later.push(unapplied)
- });
+ log!(
+ debug,
+ "deferring slash of {:?}% happened in {:?} (reported in {:?}) to {:?}",
+ slash_fraction,
+ slash_era,
+ active_era,
+ slash_era + slash_defer_duration + 1,
+ );
+ <Self as Store>::UnappliedSlashes::mutate(
+ slash_era.saturating_add(slash_defer_duration).saturating_add(One::one()),
+ move |for_later| for_later.push(unapplied),
+ );
  add_db_reads_writes(1, 1);
  }
  } else {

frame/staking/src/pallet/mod.rs

@@ -477,10 +477,6 @@ pub mod pallet {
  ValueQuery,
  >;
 
- /// The earliest era for which we have a pending, unapplied slash.
- #[pallet::storage]
- pub(crate) type EarliestUnappliedSlash<T> = StorageValue<_, EraIndex>;
-
  /// The last planned session scheduled by the session pallet.
  ///
  /// This is basically in sync with the call to [`pallet_session::SessionManager::new_session`].

frame/staking/src/tests.rs

@@ -2777,12 +2777,103 @@ fn deferred_slashes_are_deferred() {
  assert_eq!(Balances::free_balance(11), 1000);
  assert_eq!(Balances::free_balance(101), 2000);
 
+ System::reset_events();
+
  // at the start of era 4, slashes from era 1 are processed,
  // after being deferred for at least 2 full eras.
  mock::start_active_era(4);
 
  assert_eq!(Balances::free_balance(11), 900);
  assert_eq!(Balances::free_balance(101), 2000 - (nominated_value / 10));
+
+ assert_eq!(
+ staking_events_since_last_call(),
+ vec![
+ Event::StakersElected,
+ Event::EraPaid(3, 11075, 33225),
+ Event::Slashed(11, 100),
+ Event::Slashed(101, 12)
+ ]
+ );
+ })
+}
+
+#[test]
+fn retroactive_deferred_slashes_two_eras_before() {
+ ExtBuilder::default().slash_defer_duration(2).build_and_execute(|| {
+ assert_eq!(BondingDuration::get(), 3);
+
+ mock::start_active_era(1);
+ let exposure_11_at_era1 = Staking::eras_stakers(active_era(), 11);
+
+ mock::start_active_era(3);
+ on_offence_in_era(
+ &[OffenceDetails { offender: (11, exposure_11_at_era1), reporters: vec![] }],
+ &[Perbill::from_percent(10)],
+ 1, // should be deferred for two full eras, and applied at the beginning of era 4.
+ DisableStrategy::Never,
+ );
+ System::reset_events();
+
+ mock::start_active_era(4);
+
+ assert_eq!(
+ staking_events_since_last_call(),
+ vec![
+ Event::StakersElected,
+ Event::EraPaid(3, 7100, 21300),
+ Event::Slashed(11, 100),
+ Event::Slashed(101, 12)
+ ]
+ );
+ })
+}
+
+#[test]
+fn retroactive_deferred_slashes_one_before() {
+ ExtBuilder::default().slash_defer_duration(2).build_and_execute(|| {
+ assert_eq!(BondingDuration::get(), 3);
+
+ mock::start_active_era(1);
+ let exposure_11_at_era1 = Staking::eras_stakers(active_era(), 11);
+
+ // unbond at slash era.
+ mock::start_active_era(2);
+ assert_ok!(Staking::chill(Origin::signed(10)));
+ assert_ok!(Staking::unbond(Origin::signed(10), 100));
+
+ mock::start_active_era(3);
+ on_offence_in_era(
+ &[OffenceDetails { offender: (11, exposure_11_at_era1), reporters: vec![] }],
+ &[Perbill::from_percent(10)],
+ 2, // should be deferred for two full eras, and applied at the beginning of era 5.
+ DisableStrategy::Never,
+ );
+ System::reset_events();
+
+ mock::start_active_era(4);
+ assert_eq!(
+ staking_events_since_last_call(),
+ vec![Event::StakersElected, Event::EraPaid(3, 11075, 33225)]
+ );
+
+ assert_eq!(Staking::ledger(10).unwrap().total, 1000);
+ // slash happens after the next line.
+ mock::start_active_era(5);
+ assert_eq!(
+ staking_events_since_last_call(),
+ vec![
+ Event::StakersElected,
+ Event::EraPaid(4, 11075, 33225),
+ Event::Slashed(11, 100),
+ Event::Slashed(101, 12)
+ ]
+ );
+
+ // their ledger has already been slashed.
+ assert_eq!(Staking::ledger(10).unwrap().total, 900);
+ assert_ok!(Staking::unbond(Origin::signed(10), 1000));
+ assert_eq!(Staking::ledger(10).unwrap().total, 900);
  })
 }
 
@@ -2871,6 +2962,7 @@ fn remove_deferred() {
  assert_eq!(Balances::free_balance(101), 2000);
  let nominated_value = exposure.others.iter().find(|o| o.who == 101).unwrap().value;
 
+ // deferred to start of era 4.
  on_offence_now(
  &[OffenceDetails { offender: (11, exposure.clone()), reporters: vec![] }],
  &[Perbill::from_percent(10)],
@@ -2881,6 +2973,7 @@ fn remove_deferred() {
 
  mock::start_active_era(2);
 
+ // reported later, but deferred to start of era 4 as well.
  on_offence_in_era(
  &[OffenceDetails { offender: (11, exposure.clone()), reporters: vec![] }],
  &[Perbill::from_percent(15)],
@@ -2894,7 +2987,8 @@ fn remove_deferred() {
  Error::<Test>::EmptyTargets
  );
 
- assert_ok!(Staking::cancel_deferred_slash(Origin::root(), 1, vec![0]));
+ // cancel one of them.
+ assert_ok!(Staking::cancel_deferred_slash(Origin::root(), 4, vec![0]));
 
  assert_eq!(Balances::free_balance(11), 1000);
  assert_eq!(Balances::free_balance(101), 2000);
@@ -2906,13 +3000,19 @@ fn remove_deferred() {
 
  // at the start of era 4, slashes from era 1 are processed,
  // after being deferred for at least 2 full eras.
+ System::reset_events();
  mock::start_active_era(4);
 
- // the first slash for 10% was cancelled, so no effect.
- assert_eq!(Balances::free_balance(11), 1000);
- assert_eq!(Balances::free_balance(101), 2000);
-
- mock::start_active_era(5);
+ // the first slash for 10% was cancelled, but the 15% one
+ assert_eq!(
+ staking_events_since_last_call(),
+ vec![
+ Event::StakersElected,
+ Event::EraPaid(3, 11075, 33225),
+ Event::Slashed(11, 50),
+ Event::Slashed(101, 7)
+ ]
+ );
 
  let slash_10 = Perbill::from_percent(10);
  let slash_15 = Perbill::from_percent(15);
@@ -2965,7 +3065,7 @@ fn remove_multi_deferred() {
  &[Perbill::from_percent(25)],
  );
 
- assert_eq!(<Staking as Store>::UnappliedSlashes::get(&1).len(), 5);
+ assert_eq!(<Staking as Store>::UnappliedSlashes::get(&4).len(), 5);
 
  // fails if list is not sorted
  assert_noop!(
@@ -2983,9 +3083,9 @@ fn remove_multi_deferred() {
  Error::<Test>::InvalidSlashIndex
  );
 
- assert_ok!(Staking::cancel_deferred_slash(Origin::root(), 1, vec![0, 2, 4]));
+ assert_ok!(Staking::cancel_deferred_slash(Origin::root(), 4, vec![0, 2, 4]));
 
- let slashes = <Staking as Store>::UnappliedSlashes::get(&1);
+ let slashes = <Staking as Store>::UnappliedSlashes::get(&4);
  assert_eq!(slashes.len(), 2);
  assert_eq!(slashes[0].validator, 21);
  assert_eq!(slashes[1].validator, 42);