From e05bf5b320d586d84ae5d5aea8a5064cb9756bb8 Mon Sep 17 00:00:00 2001
From: Felix Lange <fjl@twurst.com>
Date: Wed, 24 Sep 2025 12:27:26 +0200
Subject: [PATCH] core/txpool/blobpool: wait for billy conversion to exit

---
 core/txpool/blobpool/blobpool.go   |  6 ++-
 core/txpool/blobpool/conversion.go | 63 +++++++++++++++++++++---------
 2 files changed, 49 insertions(+), 20 deletions(-)

diff --git a/core/txpool/blobpool/blobpool.go b/core/txpool/blobpool/blobpool.go
index 3869d3ebf6..679529b286 100644
--- a/core/txpool/blobpool/blobpool.go
+++ b/core/txpool/blobpool/blobpool.go
@@ -904,7 +904,9 @@ func (p *BlobPool) Reset(oldHead, newHead *types.Header) {
 			}
 		}
 		// Initiate the background conversion thread.
-		go p.convertLegacySidecars(ids, txs)
+		p.cQueue.launchBillyConversion(func() {
+			p.convertLegacySidecars(ids, txs)
+		})
 	}
 }
 
@@ -913,7 +915,7 @@ func (p *BlobPool) Reset(oldHead, newHead *types.Header) {
 // bulk conversion. If it fails for some reason, the subsequent txs won't be dropped
 // for simplicity which we assume it's very likely to happen.
 //
-// The returned flag indicates whether the replacement succeeds or not.
+// The returned flag indicates whether the replacement succeeded.
 func (p *BlobPool) compareAndSwap(address common.Address, hash common.Hash, blob []byte, oldID uint64, oldStorageSize uint32) bool {
 	p.lock.Lock()
 	defer p.lock.Unlock()
diff --git a/core/txpool/blobpool/conversion.go b/core/txpool/blobpool/conversion.go
index 5026892fc8..818997869c 100644
--- a/core/txpool/blobpool/conversion.go
+++ b/core/txpool/blobpool/conversion.go
@@ -32,8 +32,8 @@ import (
 // with 6 blobs each) would consume approximately 1.5GB of memory.
 const maxPendingConversionTasks = 2048
 
-// cTask represents a conversion task with an attached legacy blob transaction.
-type cTask struct {
+// txConvert represents a conversion task with an attached legacy blob transaction.
+type txConvert struct {
 	tx   *types.Transaction // Legacy blob transaction
 	done chan error         // Channel for signaling back if the conversion succeeds
 }
@@ -43,7 +43,8 @@ type cTask struct {
 // it is performed in the background by a single thread, ensuring the main Geth
 // process is not overloaded.
 type conversionQueue struct {
-	tasks  chan *cTask
+	tasks  chan *txConvert
+	billy  chan func()
 	quit   chan struct{}
 	closed chan struct{}
 }
@@ -51,7 +52,8 @@ type conversionQueue struct {
 // newConversionQueue constructs the conversion queue.
 func newConversionQueue() *conversionQueue {
 	q := &conversionQueue{
-		tasks:  make(chan *cTask),
+		tasks:  make(chan *txConvert),
+		billy:  make(chan func()),
 		quit:   make(chan struct{}),
 		closed: make(chan struct{}),
 	}
@@ -66,13 +68,23 @@ func newConversionQueue() *conversionQueue {
 func (q *conversionQueue) convert(tx *types.Transaction) error {
 	done := make(chan error, 1)
 	select {
-	case q.tasks <- &cTask{tx: tx, done: done}:
+	case q.tasks <- &txConvert{tx: tx, done: done}:
 		return <-done
 	case <-q.closed:
 		return errors.New("conversion queue closed")
 	}
 }
 
+// launchBillyConversion starts a conversion task in the background.
+func (q *conversionQueue) launchBillyConversion(fn func()) error {
+	select {
+	case q.billy <- fn:
+		return nil
+	case <-q.closed:
+		return errors.New("conversion queue closed")
+	}
+}
+
 // close terminates the conversion queue.
 func (q *conversionQueue) close() {
 	select {
@@ -85,7 +97,7 @@ func (q *conversionQueue) close() {
 }
 
 // run converts a batch of legacy blob txs to the new cell proof format.
-func (q *conversionQueue) run(tasks []*cTask, done chan struct{}, interrupt *atomic.Int32) {
+func (q *conversionQueue) run(tasks []*txConvert, done chan struct{}, interrupt *atomic.Int32) {
 	defer close(done)
 
 	for _, t := range tasks {
@@ -110,42 +122,57 @@ func (q *conversionQueue) loop() {
 	defer close(q.closed)
 
 	var (
-		done      chan struct{} // Non-nil if background routine is active
-		interrupt *atomic.Int32 // Flag to signal conversion interruption
+		billyDone  = make(chan struct{})
+		billyTasks int           // Count of running billy conversion tasks
+		done       chan struct{} // Non-nil if background routine is active
+		interrupt  *atomic.Int32 // Flag to signal conversion interruption
 
 		// The pending tasks for sidecar conversion. We assume the number of legacy
 		// blob transactions requiring conversion will not be excessive. However,
 		// a hard cap is applied as a protective measure.
-		cTasks []*cTask
+		txTasks []*txConvert
 	)
 	for {
 		select {
 		case t := <-q.tasks:
-			if len(cTasks) >= maxPendingConversionTasks {
+			if len(txTasks) >= maxPendingConversionTasks {
 				t.done <- errors.New("conversion queue is overloaded")
 				continue
 			}
-			cTasks = append(cTasks, t)
+			txTasks = append(txTasks, t)
 
 			// Launch the background conversion thread if it's idle
 			if done == nil {
 				done, interrupt = make(chan struct{}), new(atomic.Int32)
 
-				tasks := slices.Clone(cTasks)
-				cTasks = cTasks[:0]
+				tasks := slices.Clone(txTasks)
+				txTasks = txTasks[:0]
 				go q.run(tasks, done, interrupt)
 			}
 
+		case fn := <-q.billy:
+			billyTasks++
+			go func() {
+				fn()
+				billyDone <- struct{}{}
+			}()
+
 		case <-done:
 			done, interrupt = nil, nil
 
+		case <-billyDone:
+			billyTasks--
+
 		case <-q.quit:
-			if done == nil {
-				return
+			if done != nil {
+				interrupt.Store(1)
+				log.Debug("Waiting for blob proof conversion to exit")
+				<-done
+			}
+			for billyTasks > 0 {
+				<-billyDone
+				billyTasks--
 			}
-			interrupt.Store(1)
-			log.Debug("Waiting for blob proof conversion to exit")
-			<-done
 			return
 		}
 	}