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validation: Guard the active_chainstate with cs_main

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This avoids a potential race-condition where a thread is reading the
ChainstateManager::m_active_chainstate pointer while another one is
writing to it. There is no portable guarantee that reading/writing the
pointer is thread-safe.

This is also done in way that mimics ::ChainstateActive(), so the
transition from that function to this method is easy.

More discussion:
1. https://github.com/bitcoin/bitcoin/pull/20749#discussion_r559544027
2. https://github.com/bitcoin/bitcoin/pull/19806#discussion_r561023961
3. https://github.com/bitcoin/bitcoin/pull/19806#issuecomment-768946522
4. https://github.com/bitcoin/bitcoin/pull/19806#issuecomment-768955695
This commit is contained in:
Carl Dong 2021-01-27 16:20:59 -05:00
parent e130ff38c9
commit f92dc6557a
2 changed files with 8 additions and 3 deletions
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9
src/validation.cpp
View file

@ -5143,6 +5143,7 @@ double GuessVerificationProgress(const ChainTxData& data, const CBlockIndex *pin
}
Optional<uint256> ChainstateManager::SnapshotBlockhash() const {
LOCK(::cs_main); // for m_active_chainstate access
if (m_active_chainstate != nullptr) {
// If a snapshot chainstate exists, it will always be our active.
return m_active_chainstate->m_from_snapshot_blockhash;
@ -5189,13 +5190,14 @@ CChainState& ChainstateManager::InitializeChainstate(CTxMemPool& mempool, const
CChainState& ChainstateManager::ActiveChainstate() const
{
LOCK(::cs_main);
assert(m_active_chainstate);
return *m_active_chainstate;
}
bool ChainstateManager::IsSnapshotActive() const
{
return m_snapshot_chainstate && m_active_chainstate == m_snapshot_chainstate.get();
return m_snapshot_chainstate && WITH_LOCK(::cs_main, return m_active_chainstate) == m_snapshot_chainstate.get();
}
CChainState& ChainstateManager::ValidatedChainstate() const
@ -5226,7 +5228,10 @@ void ChainstateManager::Reset()
{
m_ibd_chainstate.reset();
m_snapshot_chainstate.reset();
m_active_chainstate = nullptr;
{
LOCK(::cs_main);
m_active_chainstate = nullptr;
}
m_snapshot_validated = false;
}

2
src/validation.h
View file

@ -817,7 +817,7 @@ private:
//! This is especially important when, e.g., calling ActivateBestChain()
//! on all chainstates because we are not able to hold ::cs_main going into
//! that call.
CChainState* m_active_chainstate{nullptr};
CChainState* m_active_chainstate GUARDED_BY(::cs_main) {nullptr};
//! If true, the assumed-valid chainstate has been fully validated
//! by the background validation chainstate.