program: fix risk reduction dlp burn from not being step size

CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixes
 
+- program: standardize lp shares in attempt_burn_user_lp_shares_for_risk_reduction ([#826](https://github.com/drift-labs/protocol-v2/pull/826))
+
 ### Breaking
 
 ## [2.54.0] - 2023-01-15

programs/drift/src/controller/lp.rs

@@ -2,7 +2,7 @@
 
 use crate::bn::U192;
 use crate::controller;
-use crate::controller::position::PositionDelta;
+use crate::controller::position::{get_position_index, PositionDelta};
 use crate::controller::position::{update_position_and_market, update_quote_asset_amount};
 use crate::emit;
 use crate::error::{DriftResult, ErrorCode};
@@ -357,8 +357,13 @@
     market_index: u16,
     now: i64,
 ) -> DriftResult<()> {
+    let position_index = get_position_index(&user.perp_positions, market_index)?;
+
     // standardize n shares to burn
-    let shares_to_burn: u64 = {
+    // account for issue where lp shares are smaller than step size
+    let shares_to_burn = if user.perp_positions[position_index].lp_shares == shares_to_burn {
+        shares_to_burn
+    } else {
         let market = perp_market_map.get_ref(&market_index)?;
         crate::math::orders::standardize_base_asset_amount(
             shares_to_burn.cast()?,
@@ -382,7 +387,7 @@
 
     controller::funding::settle_funding_payment(user, &user_key, &mut market, now)?;
 
-    let position = user.get_perp_position_mut(market_index)?;
+    let position = &mut user.perp_positions[position_index];
 
     validate!(
         position.lp_shares >= shares_to_burn,

programs/drift/src/controller/orders.rs

@@ -1,6 +1,6 @@
 use std::cell::RefMut;
 use std::collections::BTreeMap;
-use std::ops::DerefMut;
+use std::ops::{DerefMut, Div};
 use std::u64;
 
 use anchor_lang::prelude::*;
@@ -2890,10 +2890,14 @@
     };
 
     let order_step_size = market.amm.order_step_size;
+
+    let lp_shares_to_burn =
+        standardize_base_asset_amount(lp_shares.div(3), order_step_size)?.max(lp_shares);
+
     let (position_delta, pnl) = burn_lp_shares(
         &mut user.perp_positions[position_index],
         &mut market,
-        lp_shares.safe_div(3)?.max(order_step_size),
+        lp_shares_to_burn,
         oracle_price,
     )?;
 
@@ -2902,7 +2906,7 @@
         ts: clock.unix_timestamp,
         action: LPAction::RemoveLiquidity,
         user: user_key,
-        n_shares: lp_shares,
+        n_shares: lp_shares_to_burn,
         market_index,
         delta_base_asset_amount: position_delta.base_asset_amount,
         delta_quote_asset_amount: position_delta.quote_asset_amount,