stake-pool: Prefund split account during redelegate (#5285)

* stake-pool: Prefund split account during redelegate

* stake-pool-js: Add reserve account to redelegate

* Only pre-fund the rent-exempt reserve if needed

* Add error type for depleting the reserve during rebalance

* Do not deplete the reserve while funding rent-exemption

* Move error check for overdraw

stake-pool/js/src/index.ts

@@ -1092,6 +1092,7 @@ export async function redelegate(props: RedelegateProps) {
       stakePool: stakePool.pubkey,
       staker: stakePool.account.data.staker,
       validatorList: stakePool.account.data.validatorList,
+      reserveStake: stakePool.account.data.reserveStake,
       stakePoolWithdrawAuthority,
       ephemeralStake,
       ephemeralStakeSeed,

stake-pool/js/src/instructions.ts

@@ -325,6 +325,7 @@ export type RedelegateParams = {
   staker: PublicKey;
   stakePoolWithdrawAuthority: PublicKey;
   validatorList: PublicKey;
+  reserveStake: PublicKey;
   sourceValidatorStake: PublicKey;
   sourceTransientStake: PublicKey;
   ephemeralStake: PublicKey;
@@ -841,6 +842,7 @@ export class StakePoolInstruction {
       staker,
       stakePoolWithdrawAuthority,
       validatorList,
+      reserveStake,
       sourceValidatorStake,
       sourceTransientStake,
       ephemeralStake,
@@ -858,6 +860,7 @@ export class StakePoolInstruction {
       { pubkey: staker, isSigner: true, isWritable: false },
       { pubkey: stakePoolWithdrawAuthority, isSigner: false, isWritable: false },
       { pubkey: validatorList, isSigner: false, isWritable: true },
+      { pubkey: reserveStake, isSigner: false, isWritable: true },
       { pubkey: sourceValidatorStake, isSigner: false, isWritable: true },
       { pubkey: sourceTransientStake, isSigner: false, isWritable: true },
       { pubkey: ephemeralStake, isSigner: false, isWritable: true },

stake-pool/program/src/error.rs

@@ -149,6 +149,11 @@ pub enum StakePoolError {
     /// Provided mint does not have 9 decimals to match SOL
     #[error("IncorrectMintDecimals")]
     IncorrectMintDecimals,
+    /// Pool reserve does not have enough lamports to fund rent-exempt reserve in split
+    /// destination. Deposit more SOL in reserve, or pre-fund split destination with
+    /// the rent-exempt reserve for a stake account.
+    #[error("ReserveDepleted")]
+    ReserveDepleted,
 }
 impl From<StakePoolError> for ProgramError {
     fn from(e: StakePoolError) -> Self {

stake-pool/program/src/instruction.rs

@@ -487,34 +487,36 @@ pub enum StakePoolInstruction {
     /// The instruction only succeeds if the source transient stake account and
     /// ephemeral stake account do not exist.
     ///
-    /// The amount of lamports to move must be at least twice rent-exemption
-    /// plus the minimum delegation amount. Rent-exemption is required for the
-    /// source transient stake account, and rent-exemption plus minimum delegation
+    /// The amount of lamports to move must be at least rent-exemption plus the
+    /// minimum delegation amount. Rent-exemption plus minimum delegation
     /// is required for the destination ephemeral stake account.
     ///
+    /// The rent-exemption for the source transient account comes from the stake
+    /// pool reserve, if needed.
+    ///
     /// The amount that arrives at the destination validator in the end is
-    /// `redelegate_lamports - 2 * rent_exemption` if the destination transient
-    /// account does *not* exist, and `redelegate_lamports - rent_exemption` if
-    /// the destination transient account already exists. One `rent_exemption`
-    /// is deactivated with the source transient account during redelegation,
-    /// and another `rent_exemption` is deactivated when creating the destination
-    /// transient stake account.
+    /// `redelegate_lamports - rent_exemption` if the destination transient
+    /// account does *not* exist, and `redelegate_lamports` if the destination
+    /// transient account already exists. The `rent_exemption` is not activated
+    /// when creating the destination transient stake account, but if it already
+    /// exists, then the full amount is delegated.
     ///
     ///  0. `[]` Stake pool
     ///  1. `[s]` Stake pool staker
     ///  2. `[]` Stake pool withdraw authority
     ///  3. `[w]` Validator list
-    ///  4. `[w]` Source canonical stake account to split from
-    ///  5. `[w]` Source transient stake account to receive split and be redelegated
-    ///  6. `[w]` Uninitialized ephemeral stake account to receive redelegation
-    ///  7. `[w]` Destination transient stake account to receive ephemeral stake by merge
-    ///  8. `[]` Destination stake account to receive transient stake after activation
-    ///  9. `[]` Destination validator vote account
-    /// 10. `[]` Clock sysvar
-    /// 11. `[]` Stake History sysvar
-    /// 12. `[]` Stake Config sysvar
-    /// 13. `[]` System program
-    /// 14. `[]` Stake program
+    ///  4. `[w]` Reserve stake account, to withdraw rent exempt reserve
+    ///  5. `[w]` Source canonical stake account to split from
+    ///  6. `[w]` Source transient stake account to receive split and be redelegated
+    ///  7. `[w]` Uninitialized ephemeral stake account to receive redelegation
+    ///  8. `[w]` Destination transient stake account to receive ephemeral stake by merge
+    ///  9. `[]` Destination stake account to receive transient stake after activation
+    /// 10. `[]` Destination validator vote account
+    /// 11. `[]` Clock sysvar
+    /// 12. `[]` Stake History sysvar
+    /// 13. `[]` Stake Config sysvar
+    /// 14. `[]` System program
+    /// 15. `[]` Stake program
     Redelegate {
         /// Amount of lamports to redelegate
         #[allow(dead_code)] // but it's not
@@ -920,6 +922,7 @@ pub fn redelegate(
     staker: &Pubkey,
     stake_pool_withdraw_authority: &Pubkey,
     validator_list: &Pubkey,
+    reserve_stake: &Pubkey,
     source_validator_stake: &Pubkey,
     source_transient_stake: &Pubkey,
     ephemeral_stake: &Pubkey,
@@ -936,6 +939,7 @@ pub fn redelegate(
         AccountMeta::new_readonly(*staker, true),
         AccountMeta::new_readonly(*stake_pool_withdraw_authority, false),
         AccountMeta::new(*validator_list, false),
+        AccountMeta::new(*reserve_stake, false),
         AccountMeta::new(*source_validator_stake, false),
         AccountMeta::new(*source_transient_stake, false),
         AccountMeta::new(*ephemeral_stake, false),

stake-pool/program/src/processor.rs

@@ -1793,6 +1793,7 @@ impl Processor {
         let staker_info = next_account_info(account_info_iter)?;
         let withdraw_authority_info = next_account_info(account_info_iter)?;
         let validator_list_info = next_account_info(account_info_iter)?;
+        let reserve_stake_info = next_account_info(account_info_iter)?;
         let source_validator_stake_account_info = next_account_info(account_info_iter)?;
         let source_transient_stake_account_info = next_account_info(account_info_iter)?;
         let ephemeral_stake_account_info = next_account_info(account_info_iter)?;
@@ -1829,6 +1830,7 @@ impl Processor {
 
         stake_pool.check_validator_list(validator_list_info)?;
         check_account_owner(validator_list_info, program_id)?;
+        stake_pool.check_reserve_stake(reserve_stake_info)?;
 
         let mut validator_list_data = validator_list_info.data.borrow_mut();
         let (header, mut validator_list) =
@@ -1844,11 +1846,11 @@ impl Processor {
         let current_minimum_delegation = minimum_delegation(stake_minimum_delegation);
 
         // check that we're redelegating enough
-        let destination_transient_lamports = {
+        {
             // redelegation requires that the source account maintains rent exemption and that
             // the destination account has rent-exemption and minimum delegation
             let minimum_redelegation_lamports =
-                current_minimum_delegation.saturating_add(stake_rent.saturating_mul(2));
+                current_minimum_delegation.saturating_add(stake_rent);
             if lamports < minimum_redelegation_lamports {
                 msg!(
                     "Need more than {} lamports for redelegated stake and transient stake to meet minimum delegation requirement, {} provided",
@@ -1877,10 +1879,7 @@ impl Processor {
                 );
                 return Err(ProgramError::InsufficientFunds);
             }
-            lamports
-                .checked_sub(stake_rent)
-                .ok_or(StakePoolError::CalculationFailure)?
-        };
+        }
 
         // check source account state
         let (_, stake) = get_stake_state(source_validator_stake_account_info)?;
@@ -1945,6 +1944,25 @@ impl Processor {
                 stake_space,
             )?;
 
+            // if needed, pre-fund the rent-exempt reserve from the reserve stake
+            let required_lamports_for_rent_exemption =
+                stake_rent.saturating_sub(source_transient_stake_account_info.lamports());
+            if required_lamports_for_rent_exemption > 0 {
+                if required_lamports_for_rent_exemption >= reserve_stake_info.lamports() {
+                    return Err(StakePoolError::ReserveDepleted.into());
+                }
+                Self::stake_withdraw(
+                    stake_pool_info.key,
+                    reserve_stake_info.clone(),
+                    withdraw_authority_info.clone(),
+                    AUTHORITY_WITHDRAW,
+                    stake_pool.stake_withdraw_bump_seed,
+                    source_transient_stake_account_info.clone(),
+                    clock_info.clone(),
+                    stake_history_info.clone(),
+                    required_lamports_for_rent_exemption,
+                )?;
+            }
             Self::stake_split(
                 stake_pool_info.key,
                 source_validator_stake_account_info.clone(),
@@ -2021,7 +2039,7 @@ impl Processor {
                 u64::from(validator_stake_info.transient_stake_lamports) > 0;
             validator_stake_info.transient_stake_lamports =
                 u64::from(validator_stake_info.transient_stake_lamports)
-                    .checked_add(destination_transient_lamports)
+                    .checked_add(lamports)
                     .ok_or(StakePoolError::CalculationFailure)?
                     .into();
 
@@ -2088,7 +2106,7 @@ impl Processor {
                     withdraw_authority_info.clone(),
                     AUTHORITY_WITHDRAW,
                     stake_pool.stake_withdraw_bump_seed,
-                    destination_transient_lamports,
+                    lamports,
                     destination_transient_stake_account_info.clone(),
                 )?;
                 validator_stake_info.transient_seed_suffix =
@@ -4019,6 +4037,7 @@ impl PrintProgramError for StakePoolError {
             StakePoolError::UnsupportedFeeAccountExtension => msg!("Error: fee account has an unsupported extension"),
             StakePoolError::ExceededSlippage => msg!("Error: instruction exceeds desired slippage limit"),
             StakePoolError::IncorrectMintDecimals => msg!("Error: Provided mint does not have 9 decimals to match SOL"),
+            StakePoolError::ReserveDepleted => msg!("Error: Pool reserve does not have enough lamports to fund rent-exempt reserve in split destination. Deposit more SOL in reserve, or pre-fund split destination with the rent-exempt reserve for a stake account."),
         }
     }
 }

stake-pool/program/tests/helpers/mod.rs

@@ -1890,6 +1890,7 @@ impl StakePoolAccounts {
                 &self.staker.pubkey(),
                 &self.withdraw_authority,
                 &self.validator_list.pubkey(),
+                &self.reserve_stake.pubkey(),
                 source_validator_stake,
                 source_transient_stake,
                 ephemeral_stake,