From a19a566064893ef9016a5b077e40eaf82ed82c5a Mon Sep 17 00:00:00 2001
From: Matt Joiner <anacrolix@gmail.com>
Date: Wed, 28 May 2025 00:29:39 +1000
Subject: [PATCH] Prevent concurrent piece marking

---
 piece.go   | 2 ++
 torrent.go | 6 ++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/piece.go b/piece.go
index 78f86b15..b7c78be1 100644
--- a/piece.go
+++ b/piece.go
@@ -53,6 +53,8 @@ type Piece struct {
 	// This can include connections that have closed.
 	dirtiers map[*Peer]struct{}
 
+	// Value to twiddle to detect races.
+	race byte
 	// Currently being hashed.
 	hashing bool
 	// The piece state may have changed, and is being synchronized with storage.
diff --git a/torrent.go b/torrent.go
index a1dc80d5..c1769355 100644
--- a/torrent.go
+++ b/torrent.go
@@ -2508,9 +2508,10 @@ func (t *Torrent) pieceHashed(piece pieceIndex, passed bool, hashIoErr error) {
 		if hasDirty {
 			p.Flush() // You can be synchronous here!
 		}
+		p.race++
 		err := p.Storage().MarkComplete()
 		if err != nil {
-			t.logger.Levelf(log.Error, "error marking piece %v complete: %s", piece, err)
+			t.slogger().Error("error marking piece complete", "piece", piece, "err", err)
 		}
 		t.cl.lock()
 
@@ -2673,7 +2674,8 @@ func (t *Torrent) startHash(pi pieceIndex) {
 
 func (t *Torrent) getPieceToHash() (_ g.Option[pieceIndex]) {
 	for i := range t.piecesQueuedForHash.Iterate {
-		if t.piece(i).hashing {
+		p := t.piece(i)
+		if p.hashing || p.marking {
 			continue
 		}
 		return g.Some(i)
-- 
2.51.0