Merge bitcoin/bitcoin#26387: p2p: TryLowWorkHeadersSync follow-ups

784b023 [net processing] Simplify use of IsContinuationOfLowWorkHeadersSync in TryLowWorkHeaderSync (dergoegge)
e891aab [net processing] Fixup TryLowWorkHeadersSync comment (dergoegge)

Pull request description:

  See bitcoin/bitcoin#26355 (comment) and bitcoin/bitcoin#26355 (comment)

ACKs for top commit:
  hernanmarino:
    ACK 784b023
  brunoerg:
    crACK 784b023
  mzumsande:
    ACK 784b023

Tree-SHA512: b47ac0d78a09ca3a1806e38c5d2e2fcf1e5f0668f202450b5079c5cb168e168ac6828c0948d23f3610696375134986d75ef3c6098858173023bcb743aec8004c

Author: fanquake

src/net_processing.cpp

@@ -638,9 +638,8 @@ class PeerManagerImpl final : public PeerManager
      * @param[in]   chain_start_header  Where these headers connect in our index.
      * @param[in,out]   headers             The headers to be processed.
      *
-     * @return      True if chain was low work and a headers sync was
-     *              initiated (and headers will be empty after calling); false
-     *              otherwise.
+     * @return      True if chain was low work (headers will be empty after
+     *              calling); false otherwise.
      */
     bool TryLowWorkHeadersSync(Peer& peer, CNode& pfrom,
                                   const CBlockIndex* chain_start_header,
@@ -2563,14 +2562,10 @@ bool PeerManagerImpl::TryLowWorkHeadersSync(Peer& peer, CNode& pfrom, const CBlo
             peer.m_headers_sync.reset(new HeadersSyncState(peer.m_id, m_chainparams.GetConsensus(),
                 chain_start_header, minimum_chain_work));
 
-            // Now a HeadersSyncState object for tracking this synchronization is created,
-            // process the headers using it as normal.
-            if (!IsContinuationOfLowWorkHeadersSync(peer, pfrom, headers)) {
-                // Something went wrong, reset the headers sync.
-                peer.m_headers_sync.reset(nullptr);
-                LOCK(m_headers_presync_mutex);
-                m_headers_presync_stats.erase(peer.m_id);
-            }
+            // Now a HeadersSyncState object for tracking this synchronization
+            // is created, process the headers using it as normal. Failures are
+            // handled inside of IsContinuationOfLowWorkHeadersSync.
+            (void)IsContinuationOfLowWorkHeadersSync(peer, pfrom, headers);
         } else {
             LogPrint(BCLog::NET, "Ignoring low-work chain (height=%u) from peer=%d\n", chain_start_header->nHeight + headers.size(), pfrom.GetId());
         }