Fix a race condition in persisting options

Summary:
This patch fix a race condition in persisting options which will cause a crash when:

* Thread A obtain cf options and start to persist options based on that cf options.
* Thread B kicks in and finish DropColumnFamily and delete cf_handle.
* Thread A wakes up and tries to finish the persisting options and crashes.

Test Plan: Add a test in column_family_test that can reproduce the crash

Reviewers: anthony, IslamAbdelRahman, rven, kradhakrishnan, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D51609

db/column_family_test.cc

@@ -68,7 +68,9 @@ class ColumnFamilyTest : public testing::Test {
 
   void Close() {
     for (auto h : handles_) {
-      delete h;
+      if (h) {
+        delete h;
+      }
     }
     handles_.clear();
     names_.clear();
@@ -1260,6 +1262,81 @@ TEST_F(ColumnFamilyTest, FlushAndDropRaceCondition) {
   rocksdb::SyncPoint::GetInstance()->DisableProcessing();
 }
 
+namespace {
+std::atomic<int> test_stage(0);
+const int kMainThreadStartPersistingOptionsFile = 1;
+const int kChildThreadFinishDroppingColumnFamily = 2;
+const int kChildThreadWaitingMainThreadPersistOptions = 3;
+void DropSingleColumnFamily(ColumnFamilyTest* cf_test, int cf_id,
+                            std::vector<Comparator*> comparators) {
+  while (test_stage < kMainThreadStartPersistingOptionsFile) {
+    Env::Default()->SleepForMicroseconds(100);
+  }
+  cf_test->DropColumnFamilies({cf_id});
+  delete comparators[cf_id];
+  comparators[cf_id] = nullptr;
+  test_stage = kChildThreadFinishDroppingColumnFamily;
+}
+}  // namespace
+
+TEST_F(ColumnFamilyTest, CreateAndDropRace) {
+  const int kCfCount = 5;
+  std::vector<ColumnFamilyOptions> cf_opts;
+  std::vector<Comparator*> comparators;
+  for (int i = 0; i < kCfCount; ++i) {
+    cf_opts.emplace_back();
+    comparators.push_back(new test::SimpleSuffixReverseComparator());
+    cf_opts.back().comparator = comparators.back();
+  }
+  db_options_.create_if_missing = true;
+  db_options_.create_missing_column_families = true;
+
+  auto main_thread_id = std::this_thread::get_id();
+
+  rocksdb::SyncPoint::GetInstance()->SetCallBack("PersistRocksDBOptions:start",
+                                                 [&](void* arg) {
+    auto current_thread_id = std::this_thread::get_id();
+    // If it's the main thread hitting this sync-point, then it
+    // will be blocked until some other thread update the test_stage.
+    if (main_thread_id == current_thread_id) {
+      test_stage = kMainThreadStartPersistingOptionsFile;
+      while (test_stage < kChildThreadFinishDroppingColumnFamily) {
+        Env::Default()->SleepForMicroseconds(100);
+      }
+    }
+  });
+
+  rocksdb::SyncPoint::GetInstance()->SetCallBack(
+      "WriteThread::EnterUnbatched:Wait", [&](void* arg) {
+        // This means a thread doing DropColumnFamily() is waiting for
+        // other thread to finish persisting options.
+        // In such case, we update the test_stage to unblock the main thread.
+        test_stage = kChildThreadWaitingMainThreadPersistOptions;
+
+        // Note that based on the test setting, this must not be the
+        // main thread.
+        ASSERT_NE(main_thread_id, std::this_thread::get_id());
+      });
+
+  // Create a database with four column families
+  Open({"default", "one", "two", "three"},
+       {cf_opts[0], cf_opts[1], cf_opts[2], cf_opts[3]});
+
+  rocksdb::SyncPoint::GetInstance()->EnableProcessing();
+
+  // Start a thread that will drop the first column family
+  // and its comparator
+  std::thread drop_cf_thread(DropSingleColumnFamily, this, 1, comparators);
+
+  DropColumnFamilies({2});
+
+  drop_cf_thread.join();
+
+  Close();
+  Destroy();
+  rocksdb::SyncPoint::GetInstance()->DisableProcessing();
+}
+
 }  // namespace rocksdb
 
 int main(int argc, char** argv) {

db/db_impl.cc

@@ -1930,24 +1930,21 @@ Status DBImpl::SetOptions(ColumnFamilyHandle* column_family,
 
   MutableCFOptions new_options;
   Status s;
+  Status persist_options_status;
   {
     InstrumentedMutexLock l(&mutex_);
     s = cfd->SetOptions(options_map);
     if (s.ok()) {
       new_options = *cfd->GetLatestMutableCFOptions();
     }
-  }
-  if (s.ok()) {
-    Status persist_options_status = WriteOptionsFile();
-    if (!persist_options_status.ok()) {
-      if (db_options_.fail_if_options_file_error) {
-        s = Status::IOError(
-            "SetOptions succeeded, but unable to persist options",
-            persist_options_status.ToString());
-      }
-      Warn(db_options_.info_log,
-           "Unable to persist options in SetOptions() -- %s",
-           persist_options_status.ToString().c_str());
+    if (s.ok()) {
+      // Persist RocksDB options under the single write thread
+      WriteThread::Writer w;
+      write_thread_.EnterUnbatched(&w, &mutex_);
+
+      persist_options_status = WriteOptionsFile();
+
+      write_thread_.ExitUnbatched(&w);
     }
   }
 
@@ -1963,6 +1960,16 @@ Status DBImpl::SetOptions(ColumnFamilyHandle* column_family,
         db_options_.info_log, "[%s] SetOptions succeeded",
         cfd->GetName().c_str());
     new_options.Dump(db_options_.info_log.get());
+    if (!persist_options_status.ok()) {
+      if (db_options_.fail_if_options_file_error) {
+        s = Status::IOError(
+            "SetOptions succeeded, but unable to persist options",
+            persist_options_status.ToString());
+      }
+      Warn(db_options_.info_log,
+           "Unable to persist options in SetOptions() -- %s",
+           persist_options_status.ToString().c_str());
+    }
   } else {
     Log(InfoLogLevel::WARN_LEVEL, db_options_.info_log,
         "[%s] SetOptions failed", cfd->GetName().c_str());
@@ -3446,6 +3453,7 @@ Status DBImpl::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
                                   const std::string& column_family_name,
                                   ColumnFamilyHandle** handle) {
   Status s;
+  Status persist_options_status;
   *handle = nullptr;
 
   s = CheckCompressionSupported(cf_options);
@@ -3478,6 +3486,12 @@ Status DBImpl::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
       s = versions_->LogAndApply(
           nullptr, MutableCFOptions(opt, ImmutableCFOptions(opt)), &edit,
           &mutex_, directories_.GetDbDir(), false, &cf_options);
+
+      if (s.ok()) {
+        // If the column family was created successfully, we then persist
+        // the updated RocksDB options under the same single write thread
+        persist_options_status = WriteOptionsFile();
+      }
       write_thread_.ExitUnbatched(&w);
     }
     if (s.ok()) {
@@ -3505,7 +3519,8 @@ Status DBImpl::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
 
   // this is outside the mutex
   if (s.ok()) {
-    Status persist_options_status = WriteOptionsFile();
+    NewThreadStatusCfInfo(
+        reinterpret_cast<ColumnFamilyHandleImpl*>(*handle)->cfd());
     if (!persist_options_status.ok()) {
       if (db_options_.fail_if_options_file_error) {
         s = Status::IOError(
@@ -3517,8 +3532,6 @@ Status DBImpl::CreateColumnFamily(const ColumnFamilyOptions& cf_options,
            "Unable to persist options in CreateColumnFamily() -- %s",
            persist_options_status.ToString().c_str());
     }
-    NewThreadStatusCfInfo(
-        reinterpret_cast<ColumnFamilyHandleImpl*>(*handle)->cfd());
   }
   return s;
 }
@@ -3537,6 +3550,7 @@ Status DBImpl::DropColumnFamily(ColumnFamilyHandle* column_family) {
   edit.SetColumnFamily(cfd->GetID());
 
   Status s;
+  Status options_persist_status;
   {
     InstrumentedMutexLock l(&mutex_);
     if (cfd->IsDropped()) {
@@ -3548,6 +3562,11 @@ Status DBImpl::DropColumnFamily(ColumnFamilyHandle* column_family) {
       write_thread_.EnterUnbatched(&w, &mutex_);
       s = versions_->LogAndApply(cfd, *cfd->GetLatestMutableCFOptions(),
                                  &edit, &mutex_);
+      if (s.ok()) {
+        // If the column family was dropped successfully, we then persist
+        // the updated RocksDB options under the same single write thread
+        options_persist_status = WriteOptionsFile();
+      }
       write_thread_.ExitUnbatched(&w);
     }
 
@@ -3574,7 +3593,9 @@ Status DBImpl::DropColumnFamily(ColumnFamilyHandle* column_family) {
     auto* mutable_cf_options = cfd->GetLatestMutableCFOptions();
     max_total_in_memory_state_ -= mutable_cf_options->write_buffer_size *
                                   mutable_cf_options->max_write_buffer_number;
-    auto options_persist_status = WriteOptionsFile();
+    Log(InfoLogLevel::INFO_LEVEL, db_options_.info_log,
+        "Dropped column family with id %u\n", cfd->GetID());
+
     if (!options_persist_status.ok()) {
       if (db_options_.fail_if_options_file_error) {
         s = Status::IOError(
@@ -3586,9 +3607,6 @@ Status DBImpl::DropColumnFamily(ColumnFamilyHandle* column_family) {
            "Unable to persist options in DropColumnFamily() -- %s",
            options_persist_status.ToString().c_str());
     }
-    Log(InfoLogLevel::INFO_LEVEL, db_options_.info_log,
-        "Dropped column family with id %u\n",
-        cfd->GetID());
   } else {
     Log(InfoLogLevel::ERROR_LEVEL, db_options_.info_log,
         "Dropping column family with id %u FAILED -- %s\n",
@@ -5024,7 +5042,12 @@ Status DB::Open(const DBOptions& db_options, const std::string& dbname,
     }
   }
   TEST_SYNC_POINT("DBImpl::Open:Opened");
+  Status persist_options_status;
   if (s.ok()) {
+    // Persist RocksDB Options before scheduling the compaction.
+    // The WriteOptionsFile() will release and lock the mutex internally.
+    persist_options_status = impl->WriteOptionsFile();
+
     *dbptr = impl;
     impl->opened_successfully_ = true;
     impl->MaybeScheduleFlushOrCompaction();
@@ -5035,8 +5058,6 @@ Status DB::Open(const DBOptions& db_options, const std::string& dbname,
     Log(InfoLogLevel::INFO_LEVEL, impl->db_options_.info_log, "DB pointer %p",
         impl);
     LogFlush(impl->db_options_.info_log);
-
-    auto persist_options_status = impl->WriteOptionsFile();
     if (!persist_options_status.ok()) {
       if (db_options.fail_if_options_file_error) {
         s = Status::IOError(
@@ -5165,38 +5186,34 @@ Status DestroyDB(const std::string& dbname, const Options& options) {
 
 Status DBImpl::WriteOptionsFile() {
 #ifndef ROCKSDB_LITE
-  std::string file_name;
-  Status s = WriteOptionsToTempFile(&file_name);
-  if (!s.ok()) {
-    return s;
-  }
-  s = RenameTempFileToOptionsFile(file_name);
-  return s;
-#else
-  return Status::OK();
-#endif  // !ROCKSDB_LITE
-}
+  mutex_.AssertHeld();
 
-Status DBImpl::WriteOptionsToTempFile(std::string* file_name) {
-#ifndef ROCKSDB_LITE
   std::vector<std::string> cf_names;
   std::vector<ColumnFamilyOptions> cf_opts;
-  {
-    InstrumentedMutexLock l(&mutex_);
-    // This part requires mutex to protect the column family options
-    for (auto cfd : *versions_->GetColumnFamilySet()) {
-      if (cfd->IsDropped()) {
-        continue;
-      }
-      cf_names.push_back(cfd->GetName());
-      cf_opts.push_back(BuildColumnFamilyOptions(
-          *cfd->options(), *cfd->GetLatestMutableCFOptions()));
+
+  // This part requires mutex to protect the column family options
+  for (auto cfd : *versions_->GetColumnFamilySet()) {
+    if (cfd->IsDropped()) {
+      continue;
     }
+    cf_names.push_back(cfd->GetName());
+    cf_opts.push_back(BuildColumnFamilyOptions(
+        *cfd->options(), *cfd->GetLatestMutableCFOptions()));
   }
-  *file_name = TempOptionsFileName(GetName(), versions_->NewFileNumber());
 
-  Status s = PersistRocksDBOptions(GetDBOptions(), cf_names, cf_opts,
-                                   *file_name, GetEnv());
+  // Unlock during expensive operations.  New writes cannot get here
+  // because the single write thread ensures all new writes get queued.
+  mutex_.Unlock();
+
+  std::string file_name =
+      TempOptionsFileName(GetName(), versions_->NewFileNumber());
+  Status s = PersistRocksDBOptions(GetDBOptions(), cf_names, cf_opts, file_name,
+                                   GetEnv());
+
+  if (s.ok()) {
+    s = RenameTempFileToOptionsFile(file_name);
+  }
+  mutex_.Lock();
   return s;
 #else
   return Status::OK();
@@ -5224,8 +5241,6 @@ void DeleteOptionsFilesHelper(const std::map<uint64_t, std::string>& filenames,
 
 Status DBImpl::DeleteObsoleteOptionsFiles() {
 #ifndef ROCKSDB_LITE
-  options_files_mutex_.AssertHeld();
-
   std::vector<std::string> filenames;
   // use ordered map to store keep the filenames sorted from the newest
   // to the oldest.
@@ -5257,7 +5272,6 @@ Status DBImpl::DeleteObsoleteOptionsFiles() {
 
 Status DBImpl::RenameTempFileToOptionsFile(const std::string& file_name) {
 #ifndef ROCKSDB_LITE
-  InstrumentedMutexLock l(&options_files_mutex_);
   Status s;
   std::string options_file_name =
       OptionsFileName(GetName(), versions_->NewFileNumber());

db/db_impl.h

@@ -405,10 +405,14 @@ class DBImpl : public DB {
                                         SuperVersion* super_version,
                                         Arena* arena);
 
-  // The following options file related functions should not be
-  // called while DB mutex is held.
+  // Except in DB::Open(), WriteOptionsFile can only be called when:
+  // 1. WriteThread::Writer::EnterUnbatched() is used.
+  // 2. db_mutex is held
   Status WriteOptionsFile();
-  Status WriteOptionsToTempFile(std::string* file_name);
+
+  // The following two functions can only be called when:
+  // 1. WriteThread::Writer::EnterUnbatched() is used.
+  // 2. db_mutex is NOT held
   Status RenameTempFileToOptionsFile(const std::string& file_name);
   Status DeleteObsoleteOptionsFiles();
 

db/write_thread.cc

@@ -4,6 +4,7 @@
 //  of patent rights can be found in the PATENTS file in the same directory.
 
 #include "db/write_thread.h"
+#include "util/sync_point.h"
 
 namespace rocksdb {
 
@@ -188,6 +189,7 @@ void WriteThread::EnterUnbatched(Writer* w, InstrumentedMutex* mu) {
   LinkOne(w, &wait_needed);
   if (wait_needed) {
     mu->Unlock();
+    TEST_SYNC_POINT("WriteThread::EnterUnbatched:Wait");
     Await(w);
     mu->Lock();
   }

util/options_parser.cc

@@ -17,6 +17,7 @@
 #include "rocksdb/db.h"
 #include "util/options_helper.h"
 #include "util/string_util.h"
+#include "util/sync_point.h"
 
 #include "port/port.h"
 
@@ -34,6 +35,7 @@ Status PersistRocksDBOptions(const DBOptions& db_opt,
                              const std::vector<std::string>& cf_names,
                              const std::vector<ColumnFamilyOptions>& cf_opts,
                              const std::string& file_name, Env* env) {
+  TEST_SYNC_POINT("PersistRocksDBOptions:start");
   if (cf_names.size() != cf_opts.size()) {
     return Status::InvalidArgument(
         "cf_names.size() and cf_opts.size() must be the same");