diff options
author | Ryan Ofsky <ryan@ofsky.org> | 2022-09-30 08:44:04 -0400 |
---|---|---|
committer | Ryan Ofsky <ryan@ofsky.org> | 2022-10-05 11:06:58 -0400 |
commit | 8891949bdcb25093d3a6703ae8228c3c3687d3a4 (patch) | |
tree | 0db028395713f658e0c9554d9816b20f9c3f7ca9 | |
parent | 33eef562a321ce772a9a88073a78a85894cb3fe8 (diff) | |
download | bitcoin-8891949bdcb25093d3a6703ae8228c3c3687d3a4.tar.xz |
index: Improve BaseIndex::BlockUntilSyncedToCurrentChain reliability
Since commit f08c9fb0c6a799e3cb75ca5f763a746471625beb from PR
https://github.com/bitcoin/bitcoin/pull/21726, index
`BlockUntilSyncedToCurrentChain` behavior has been less reliable, and there has
also been a race condition in the `coinstatsindex_initial_sync` unit test.
It seems better for `BlockUntilSyncedToCurrentChain` to actually wait for the
last connected block to be fully processed, than to be able to return before
prune locks are set, so this switches the order of `m_best_block_index =
block;` and `UpdatePruneLock` statements in `SetBestBlockIndex` to make it more
reliable.
Also since commit f08c9fb0c6a799e3cb75ca5f763a746471625beb, there has been a
race condition in the `coinstatsindex_initial_sync` test. Before that commit,
the atomic index best block pointer `m_best_block_index` was updated as the
last step of `BaseIndex::BlockConnected`, so `BlockUntilSyncedToCurrentChain`
could safely be used in tests to wait for the last `BlockConnected`
notification to be finished before stopping and destroying the index. But
after that commit, calling `BlockUntilSyncedToCurrentChain` is no longer
sufficient, and there is a race between the test shutdown code which destroys
the index object and the new code introduced in that commit calling
`AllowPrune()` and `GetName()` on the index object. Reproducibility
instructions for this are in
https://github.com/bitcoin/bitcoin/issues/25365#issuecomment-1259744133
This commit fixes the `coinstatsindex_initial_sync` race condition, even though
it will require an additional change to silence TSAN false positives,
https://github.com/bitcoin/bitcoin/pull/26188, after it is fixed. So this
partially addresses but does not resolve the bug reporting TSAN errors
https://github.com/bitcoin/bitcoin/issues/25365.
There is no known race condition outside of test code currently, because the
bitcoind `Shutdown` function calls `FlushBackgroundCallbacks` not
`BlockUntilSyncedToCurrentChain` to safely shut down.
Co-authored-by: Vasil Dimov <vd@FreeBSD.org>
Co-authored-by: MacroFake <falke.marco@gmail.com>
-rw-r--r-- | src/index/base.cpp | 13 |
1 files changed, 12 insertions, 1 deletions
diff --git a/src/index/base.cpp b/src/index/base.cpp index 88c2ce98fa..3eea09b17d 100644 --- a/src/index/base.cpp +++ b/src/index/base.cpp @@ -298,6 +298,10 @@ void BaseIndex::BlockConnected(const std::shared_ptr<const CBlock>& block, const } interfaces::BlockInfo block_info = kernel::MakeBlockInfo(pindex, block.get()); if (CustomAppend(block_info)) { + // Setting the best block index is intentionally the last step of this + // function, so BlockUntilSyncedToCurrentChain callers waiting for the + // best block index to be updated can rely on the block being fully + // processed, and the index object being safe to delete. SetBestBlockIndex(pindex); } else { FatalError("%s: Failed to write block %s to index", @@ -414,10 +418,17 @@ IndexSummary BaseIndex::GetSummary() const void BaseIndex::SetBestBlockIndex(const CBlockIndex* block) { assert(!node::fPruneMode || AllowPrune()); - m_best_block_index = block; if (AllowPrune() && block) { node::PruneLockInfo prune_lock; prune_lock.height_first = block->nHeight; WITH_LOCK(::cs_main, m_chainstate->m_blockman.UpdatePruneLock(GetName(), prune_lock)); } + + // Intentionally set m_best_block_index as the last step in this function, + // after updating prune locks above, and after making any other references + // to *this, so the BlockUntilSyncedToCurrentChain function (which checks + // m_best_block_index as an optimization) can be used to wait for the last + // BlockConnected notification and safely assume that prune locks are + // updated and that the index object is safe to delete. + m_best_block_index = block; } |