From e030b7429b764a56707f9755d6ac3d5a585faad0 Mon Sep 17 00:00:00 2001
From: Giulio rebuffo <giulio.rebuffo@gmail.com>
Date: Fri, 21 Feb 2025 09:50:47 +0100
Subject: [PATCH] Cherry-pick: fix stuck forward sync (#13892)

Cherry pick PR #13883 into `release/3.0`
---
 cl/phase1/stages/forward_sync.go | 44 +++++---------------------------
 1 file changed, 7 insertions(+), 37 deletions(-)

diff --git a/cl/phase1/stages/forward_sync.go b/cl/phase1/stages/forward_sync.go
index 7bde4554c59..68ac8cba87e 100644
--- a/cl/phase1/stages/forward_sync.go
+++ b/cl/phase1/stages/forward_sync.go
@@ -101,30 +101,6 @@ func downloadAndProcessEip4844DA(ctx context.Context, logger log.Logger, cfg *Cf
 	return highestProcessed - 1, err
 }
 
-func filterUnneededBlocks(ctx context.Context, blocks []*cltypes.SignedBeaconBlock, cfg *Cfg) []*cltypes.SignedBeaconBlock {
-	filtered := make([]*cltypes.SignedBeaconBlock, 0, len(blocks))
-	// Find the latest block in the list
-	for _, block := range blocks {
-		blockRoot, err := block.Block.HashSSZ()
-		if err != nil {
-			panic(err)
-		}
-		_, hasInFcu := cfg.forkChoice.GetHeader(blockRoot)
-
-		var hasSignedHeaderInDB bool
-		if err = cfg.indiciesDB.View(ctx, func(tx kv.Tx) error {
-			_, hasSignedHeaderInDB, err = beacon_indicies.ReadSignedHeaderByBlockRoot(ctx, tx, blockRoot)
-			return err
-		}); err != nil {
-			panic(err)
-		}
-		if !hasInFcu || !hasSignedHeaderInDB {
-			filtered = append(filtered, block)
-		}
-	}
-	return filtered
-}
-
 // processDownloadedBlockBatches processes a batch of downloaded blocks.
 // It takes the highest block processed, a flag to determine if insertion is needed, and a list of signed beacon blocks as input.
 // It returns the new highest block processed and an error if any.
@@ -134,12 +110,6 @@ func processDownloadedBlockBatches(ctx context.Context, logger log.Logger, cfg *
 		return blocks[i].Block.Slot < blocks[j].Block.Slot
 	})
 
-	// Filter out blocks that are already in the FCU or have a signed header in the DB
-	blocks = filterUnneededBlocks(ctx, blocks, cfg)
-	if len(blocks) == 0 {
-		return highestBlockProcessed, nil
-	}
-
 	var (
 		blockRoot common.Hash
 		st        *state.CachingBeaconState
@@ -228,16 +198,16 @@ func processDownloadedBlockBatches(ctx context.Context, logger log.Logger, cfg *
 // forwardSync (MAIN ROUTINE FOR ForwardSync) performs the forward synchronization of beacon blocks.
 func forwardSync(ctx context.Context, logger log.Logger, cfg *Cfg, args Args) error {
 	var (
-		shouldInsert        = cfg.executionClient != nil && cfg.executionClient.SupportInsertion() // Check if the execution client supports insertion
-		finalizedCheckpoint = cfg.forkChoice.FinalizedCheckpoint()                                 // Get the finalized checkpoint from fork choice
-		secsPerLog          = 30                                                                   // Interval in seconds for logging progress
-		logTicker           = time.NewTicker(time.Duration(secsPerLog) * time.Second)              // Ticker for logging progress
-		downloader          = network2.NewForwardBeaconDownloader(ctx, cfg.rpc)                    // Initialize a new forward beacon downloader
-		currentSlot         atomic.Uint64                                                          // Atomic variable to track the current slot
+		shouldInsert = cfg.executionClient != nil && cfg.executionClient.SupportInsertion() // Check if the execution client supports insertion
+		startSlot    = cfg.forkChoice.HighestSeen() - 8                                     // Start forwardsync a little bit behind the highest seen slot (account for potential reorgs)
+		secsPerLog   = 30                                                                   // Interval in seconds for logging progress
+		logTicker    = time.NewTicker(time.Duration(secsPerLog) * time.Second)              // Ticker for logging progress
+		downloader   = network2.NewForwardBeaconDownloader(ctx, cfg.rpc)                    // Initialize a new forward beacon downloader
+		currentSlot  atomic.Uint64                                                          // Atomic variable to track the current slot
 	)
 
 	// Initialize the slot to download from the finalized checkpoint
-	currentSlot.Store(finalizedCheckpoint.Epoch * cfg.beaconCfg.SlotsPerEpoch)
+	currentSlot.Store(startSlot)
 
 	// Always start from the current finalized checkpoint
 	downloader.SetHighestProcessedSlot(currentSlot.Load())