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Fix block index inconsistency in InvalidateBlock()

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Previously, we could release cs_main while leaving the block index in a state
that would fail CheckBlockIndex, because setBlockIndexCandidates was not being
fully populated before releasing cs_main.
This commit is contained in:
Suhas Daftuar 2019-09-10 13:58:41 -04:00
parent 1985c4efda
commit 2a4e60b482
1 changed files with 52 additions and 2 deletions
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54
src/validation.cpp
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@ -2778,6 +2778,38 @@ bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& c
bool pindex_was_in_chain = false;
int disconnected = 0;
// We do not allow ActivateBestChain() to run while InvalidateBlock() is
// running, as that could cause the tip to change while we disconnect
// blocks.
LOCK(m_cs_chainstate);
// We'll be acquiring and releasing cs_main below, to allow the validation
// callbacks to run. However, we should keep the block index in a
// consistent state as we disconnect blocks -- in particular we need to
// add equal-work blocks to setBlockIndexCandidates as we disconnect.
// To avoid walking the block index repeatedly in search of candidates,
// build a map once so that we can look up candidate blocks by chain
// work as we go.
std::multimap<const arith_uint256, CBlockIndex *> candidate_blocks_by_work;
{
LOCK(cs_main);
for (const auto& entry : m_blockman.m_block_index) {
CBlockIndex *candidate = entry.second;
// We don't need to put anything in our active chain into the
// multimap, because those candidates will be found and considered
// as we disconnect.
// Instead, consider only non-active-chain blocks that have at
// least as much work as where we expect the new tip to end up.
if (!m_chain.Contains(candidate) &&
!CBlockIndexWorkComparator()(candidate, pindex->pprev) &&
candidate->IsValid(BLOCK_VALID_TRANSACTIONS) &&
candidate->HaveTxsDownloaded()) {
candidate_blocks_by_work.insert(std::make_pair(candidate->nChainWork, candidate));
}
}
}
// Disconnect (descendants of) pindex, and mark them invalid.
while (true) {
if (ShutdownRequested()) break;
@ -2820,11 +2852,24 @@ bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& c
setDirtyBlockIndex.insert(to_mark_failed);
}
// Add any equal or more work headers to setBlockIndexCandidates
auto candidate_it = candidate_blocks_by_work.lower_bound(invalid_walk_tip->pprev->nChainWork);
while (candidate_it != candidate_blocks_by_work.end()) {
if (!CBlockIndexWorkComparator()(candidate_it->second, invalid_walk_tip->pprev)) {
setBlockIndexCandidates.insert(candidate_it->second);
candidate_it = candidate_blocks_by_work.erase(candidate_it);
} else {
++candidate_it;
}
}
// Track the last disconnected block, so we can correct its BLOCK_FAILED_CHILD status in future
// iterations, or, if it's the last one, call InvalidChainFound on it.
to_mark_failed = invalid_walk_tip;
}
CheckBlockIndex(chainparams.GetConsensus());
{
LOCK(cs_main);
if (m_chain.Contains(to_mark_failed)) {
@ -2838,8 +2883,13 @@ bool CChainState::InvalidateBlock(CValidationState& state, const CChainParams& c
setBlockIndexCandidates.erase(to_mark_failed);
m_blockman.m_failed_blocks.insert(to_mark_failed);
// The resulting new best tip may not be in setBlockIndexCandidates anymore, so
// add it again.
// If any new blocks somehow arrived while we were disconnecting
// (above), then the pre-calculation of what should go into
// setBlockIndexCandidates may have missed entries. This would
// technically be an inconsistency in the block index, but if we clean
// it up here, this should be an essentially unobservable error.
// Loop back over all block index entries and add any missing entries
// to setBlockIndexCandidates.
BlockMap::iterator it = m_blockman.m_block_index.begin();
while (it != m_blockman.m_block_index.end()) {
if (it->second->IsValid(BLOCK_VALID_TRANSACTIONS) && it->second->HaveTxsDownloaded() && !setBlockIndexCandidates.value_comp()(it->second, m_chain.Tip())) {