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backport: partial Merge bitcoin/bitcoin#26326: net: reduce LOCK(cs_main) scope in GETBLOCKTXN #7350

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backport: partial Merge bitcoin/bitcoin#26326: net: reduce LOCK(cs_main) scope in GETBLOCKTXN #7350

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17 changes: 13 additions & 4 deletions src/net_processing.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -142,6 +142,7 @@ static constexpr auto BLOCK_STALLING_TIMEOUT_MAX{64s};
static const int MAX_CMPCTBLOCK_DEPTH = 5;
/** Maximum depth of blocks we're willing to respond to GETBLOCKTXN requests for. */
static const int MAX_BLOCKTXN_DEPTH = 10;
static_assert(MAX_BLOCKTXN_DEPTH <= MIN_BLOCKS_TO_KEEP, "MAX_BLOCKTXN_DEPTH too high");
/** Size of the "block download window": how far ahead of our current height do we fetch?
* Larger windows tolerate larger download speed differences between peer, but increase the potential
* degree of disordering of blocks on disk (which make reindexing and pruning harder). We'll probably
Expand Down Expand Up @@ -4473,6 +4474,7 @@ void PeerManagerImpl::ProcessMessage(
return;
}

FlatFilePos block_pos{};
{
LOCK(cs_main);

Expand All @@ -4483,13 +4485,20 @@ void PeerManagerImpl::ProcessMessage(
}

if (pindex->nHeight >= m_chainman.ActiveChain().Height() - MAX_BLOCKTXN_DEPTH) {
CBlock block;
bool ret = ReadBlockFromDisk(block, pindex, m_chainparams.GetConsensus());
assert(ret);
block_pos = pindex->GetBlockPos();
}
}

SendBlockTransactions(pfrom, *peer, block, req);
if (!block_pos.IsNull()) {
CBlock block;
const auto hash = ReadBlockFromDisk(block, block_pos, m_chainparams.GetConsensus());
if (!hash || *hash != req.blockhash) {
LogPrint(BCLog::NET, "Peer %d sent us a getblocktxn for a block we could not read\n", pfrom.GetId());
return;
Comment on lines +4495 to 4497

@thepastaclaw thepastaclaw Jun 9, 2026

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💬 Nitpick: Log message conflates I/O failure with hash mismatch

After dropping cs_main, the failure path emits the same "a block we could not read" line for two distinct conditions: ReadBlockFromDisk returning nullopt (open/deserialize/PoW failure) and the read succeeding with *hash != req.blockhash (a stale FlatFilePos / disk-state inconsistency after the lock was released). Distinguishing these helps operators tell transient I/O or pruning issues from a position-vs-hash race. Diagnostic quality only; not a defect.

source: ['claude']

Comment on lines +4495 to 4497

@thepastaclaw thepastaclaw Jun 27, 2026

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💬 Nitpick: Log line conflates disk read failure with hash mismatch

After cs_main is released, two operationally distinct failures share one log line: ReadBlockFromDisk returning std::nullopt (OpenBlockFile failure, deserialization error, PoW header check failure — typically pruning or corruption) and a successful read whose *hash != req.blockhash (the FlatFilePos captured under cs_main no longer points at the requested block, e.g. a race with reorg/prune/reindex in the very window this PR introduces). Splitting these into two messages would make the new lock-scope reduction easier to diagnose if it surfaces in the wild. Purely diagnostic quality; behavior is correct. Existing unresolved thread: #7350 (comment).

source: ['claude', 'codex']

}

SendBlockTransactions(pfrom, *peer, block, req);
return;
}

// If an older block is requested (should never happen in practice,
Expand Down
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