Avoid deadlock between mutex_ and log_write_mutex_ (#5437)
Summary: To avoid deadlock mutex_ should never be acquired before log_write_mutex_. The patch documents that and also fixes one case in ::FlushWAL that acquires mutex_ through ::WriteStatusCheck when it already holds lock on log_write_mutex_. Pull Request resolved: https://github.com/facebook/rocksdb/pull/5437 Differential Revision: D15749722 Pulled By: maysamyabandeh fbshipit-source-id: f57b69c44b4b80cc6d7ddf3d3fdf4a9eb5a5a45a
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@ -1046,10 +1046,13 @@ int DBImpl::FindMinimumEmptyLevelFitting(
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Status DBImpl::FlushWAL(bool sync) {
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if (manual_wal_flush_) {
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// We need to lock log_write_mutex_ since logs_ might change concurrently
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InstrumentedMutexLock wl(&log_write_mutex_);
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log::Writer* cur_log_writer = logs_.back().writer;
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auto s = cur_log_writer->WriteBuffer();
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Status s;
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{
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// We need to lock log_write_mutex_ since logs_ might change concurrently
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InstrumentedMutexLock wl(&log_write_mutex_);
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log::Writer* cur_log_writer = logs_.back().writer;
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s = cur_log_writer->WriteBuffer();
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}
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if (!s.ok()) {
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ROCKS_LOG_ERROR(immutable_db_options_.info_log, "WAL flush error %s",
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s.ToString().c_str());
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@ -1521,6 +1521,8 @@ class DBImpl : public DB {
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// logfile_number_. With two_write_queues it also protects alive_log_files_,
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// and log_empty_. Refer to the definition of each variable below for more
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// details.
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// Note: to avoid dealock, if needed to acquire both log_write_mutex_ and
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// mutex_, the order should be first mutex_ and then log_write_mutex_.
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InstrumentedMutex log_write_mutex_;
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std::atomic<bool> shutting_down_;
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