From aec4fa2de0030f035d41874b2db7efdbf93bba24 Mon Sep 17 00:00:00 2001
From: Vasil Dimov <vd@FreeBSD.org>
Date: Wed, 15 Oct 2025 15:53:56 +0200
Subject: [PATCH] net: drop the only recursive usage of CConnman::m_nodes_mutex

The only recursive usage of `CConnman::m_nodes_mutex` is from
`PeerManagerImpl::MaybeSetPeerAsAnnouncingHeaderAndIDs()` which uses
nested calls to `CConnman::ForNode()` to trim the size of
`lNodesAnnouncingHeaderAndIDs` to `<= 3`. This need not be nested, so
take it out.

Before:
```
fornode(newnode)
    if (size >= 3)
        fornode(front) handle removal of front
        pop front
    push back newnode
```

After:
```
fornode(newnode)
    push back newnode
if (size > 3)
    fornode(front) handle removal of front
    pop front
```

`lNodesAnnouncingHeaderAndIDs` is protected by `cs_main` which is locked
during the entire operation.
---
 src/net_processing.cpp | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index b870df66c1e..10168d7f390 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -1309,25 +1309,25 @@ void PeerManagerImpl::MaybeSetPeerAsAnnouncingHeaderAndIDs(NodeId nodeid)
             }
         }
     }
-    m_connman.ForNode(nodeid, [this](CNode* pfrom) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
+    const bool nodeid_was_appended{m_connman.ForNode(nodeid, [this](CNode* pfrom) EXCLUSIVE_LOCKS_REQUIRED(::cs_main) {
         AssertLockHeld(::cs_main);
-        if (lNodesAnnouncingHeaderAndIDs.size() >= 3) {
-            // As per BIP152, we only get 3 of our peers to announce
-            // blocks using compact encodings.
-            m_connman.ForNode(lNodesAnnouncingHeaderAndIDs.front(), [this](CNode* pnodeStop){
-                MakeAndPushMessage(*pnodeStop, NetMsgType::SENDCMPCT, /*high_bandwidth=*/false, /*version=*/CMPCTBLOCKS_VERSION);
-                // save BIP152 bandwidth state: we select peer to be low-bandwidth
-                pnodeStop->m_bip152_highbandwidth_to = false;
-                return true;
-            });
-            lNodesAnnouncingHeaderAndIDs.pop_front();
-        }
         MakeAndPushMessage(*pfrom, NetMsgType::SENDCMPCT, /*high_bandwidth=*/true, /*version=*/CMPCTBLOCKS_VERSION);
         // save BIP152 bandwidth state: we select peer to be high-bandwidth
         pfrom->m_bip152_highbandwidth_to = true;
         lNodesAnnouncingHeaderAndIDs.push_back(pfrom->GetId());
         return true;
-    });
+    })};
+    if (nodeid_was_appended && lNodesAnnouncingHeaderAndIDs.size() > 3) {
+        // As per BIP152, we only get 3 of our peers to announce
+        // blocks using compact encodings.
+        m_connman.ForNode(lNodesAnnouncingHeaderAndIDs.front(), [this](CNode* pnodeStop) {
+            MakeAndPushMessage(*pnodeStop, NetMsgType::SENDCMPCT, /*high_bandwidth=*/false, /*version=*/CMPCTBLOCKS_VERSION);
+            // save BIP152 bandwidth state: we select peer to be low-bandwidth
+            pnodeStop->m_bip152_highbandwidth_to = false;
+            return true;
+        });
+        lNodesAnnouncingHeaderAndIDs.pop_front();
+    }
 }
 
 bool PeerManagerImpl::TipMayBeStale()