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Fix UAF race between writers and DBImpl destruction #1296

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Fix UAF race between writers and DBImpl destruction #1296

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17 changes: 13 additions & 4 deletions db/db_impl.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -150,10 +150,13 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
&internal_comparator_)) {}

DBImpl::~DBImpl() {
// Wait for background work to finish.
// Wait for background work and in-flight writes to finish.
mutex_.Lock();
shutting_down_.store(true, std::memory_order_release);
while (background_compaction_scheduled_) {
// Wake up any threads blocked in MakeRoomForWrite() or other places that wait
// for background work to finish.
background_work_finished_signal_.SignalAll();
while (background_compaction_scheduled_ || !writers_.empty()) {
background_work_finished_signal_.Wait();
}
mutex_.Unlock();
Expand Down Expand Up @@ -1219,9 +1222,9 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {

// May temporarily unlock and wait.
Status status = MakeRoomForWrite(updates == nullptr);
uint64_t last_sequence = versions_->LastSequence();
Writer* last_writer = &w;
if (status.ok() && updates != nullptr) { // nullptr batch is for compactions
uint64_t last_sequence = versions_->LastSequence();
WriteBatch* write_batch = BuildBatchGroup(&last_writer);
WriteBatchInternal::SetSequence(write_batch, last_sequence + 1);
last_sequence += WriteBatchInternal::Count(write_batch);
Expand Down Expand Up @@ -1270,6 +1273,9 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* updates) {
// Notify new head of write queue
if (!writers_.empty()) {
writers_.front()->cv.Signal();
} else {
// The writer queue is empty; wake up shutdown/destructor waiters.
background_work_finished_signal_.SignalAll();
}

return status;
Expand Down Expand Up @@ -1333,7 +1339,10 @@ Status DBImpl::MakeRoomForWrite(bool force) {
bool allow_delay = !force;
Status s;
while (true) {
if (!bg_error_.ok()) {
if (shutting_down_.load(std::memory_order_acquire)) {
s = Status::IOError("Deleting DB during MakeRoomForWrite");
break;
} else if (!bg_error_.ok()) {
// Yield previous error
s = bg_error_;
break;
Expand Down
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