From 9d50e7bc26d6ab164f3e1534f36a08d57a2be02a Mon Sep 17 00:00:00 2001
From: CPerezz <cperezz19@pm.me>
Date: Sun, 8 Feb 2026 08:51:10 +0100
Subject: [PATCH] eth/protocols/snap: restore peers to idle pool on request
 revert

All five revert*Request functions (account, bytecode, storage,
trienode heal, bytecode heal) remove the request from the tracked
set but never restore the peer to its corresponding idle pool.
When a request times out and no response arrives, the peer is
permanently lost from the idle pool, preventing new work from
being assigned to it.

In normal operation this bug is masked by pivot movement (which
resets idle pools via new Sync() cycles every ~15 minutes) and
peer churn (reconnections re-add peers via Register()). However
in scenarios with long-running sync cycles and few peers, all
peers can eventually leak out of the idle pools, stalling sync
entirely.

Fix: after deleting from the request map, restore the peer to
its idle pool if it is still registered (guards against the
peer-drop path where Unregister already removed the peer).
This mirrors the pattern used in all five On* response handlers.
---
 eth/protocols/snap/sync.go | 30 +++++++++++++++++++++++++-----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/eth/protocols/snap/sync.go b/eth/protocols/snap/sync.go
index cf4e494645..2645233e93 100644
--- a/eth/protocols/snap/sync.go
+++ b/eth/protocols/snap/sync.go
@@ -1699,9 +1699,13 @@ func (s *Syncer) revertAccountRequest(req *accountRequest) {
 	}
 	close(req.stale)
 
-	// Remove the request from the tracked set
+	// Remove the request from the tracked set and restore the peer to the
+	// idle pool so it can be reassigned work (skip if peer already left).
 	s.lock.Lock()
 	delete(s.accountReqs, req.id)
+	if _, ok := s.peers[req.peer]; ok {
+		s.accountIdlers[req.peer] = struct{}{}
+	}
 	s.lock.Unlock()
 
 	// If there's a timeout timer still running, abort it and mark the account
@@ -1740,9 +1744,13 @@ func (s *Syncer) revertBytecodeRequest(req *bytecodeRequest) {
 	}
 	close(req.stale)
 
-	// Remove the request from the tracked set
+	// Remove the request from the tracked set and restore the peer to the
+	// idle pool so it can be reassigned work (skip if peer already left).
 	s.lock.Lock()
 	delete(s.bytecodeReqs, req.id)
+	if _, ok := s.peers[req.peer]; ok {
+		s.bytecodeIdlers[req.peer] = struct{}{}
+	}
 	s.lock.Unlock()
 
 	// If there's a timeout timer still running, abort it and mark the code
@@ -1781,9 +1789,13 @@ func (s *Syncer) revertStorageRequest(req *storageRequest) {
 	}
 	close(req.stale)
 
-	// Remove the request from the tracked set
+	// Remove the request from the tracked set and restore the peer to the
+	// idle pool so it can be reassigned work (skip if peer already left).
 	s.lock.Lock()
 	delete(s.storageReqs, req.id)
+	if _, ok := s.peers[req.peer]; ok {
+		s.storageIdlers[req.peer] = struct{}{}
+	}
 	s.lock.Unlock()
 
 	// If there's a timeout timer still running, abort it and mark the storage
@@ -1826,9 +1838,13 @@ func (s *Syncer) revertTrienodeHealRequest(req *trienodeHealRequest) {
 	}
 	close(req.stale)
 
-	// Remove the request from the tracked set
+	// Remove the request from the tracked set and restore the peer to the
+	// idle pool so it can be reassigned work (skip if peer already left).
 	s.lock.Lock()
 	delete(s.trienodeHealReqs, req.id)
+	if _, ok := s.peers[req.peer]; ok {
+		s.trienodeHealIdlers[req.peer] = struct{}{}
+	}
 	s.lock.Unlock()
 
 	// If there's a timeout timer still running, abort it and mark the trie node
@@ -1867,9 +1883,13 @@ func (s *Syncer) revertBytecodeHealRequest(req *bytecodeHealRequest) {
 	}
 	close(req.stale)
 
-	// Remove the request from the tracked set
+	// Remove the request from the tracked set and restore the peer to the
+	// idle pool so it can be reassigned work (skip if peer already left).
 	s.lock.Lock()
 	delete(s.bytecodeHealReqs, req.id)
+	if _, ok := s.peers[req.peer]; ok {
+		s.bytecodeHealIdlers[req.peer] = struct{}{}
+	}
 	s.lock.Unlock()
 
 	// If there's a timeout timer still running, abort it and mark the code