From ebb9b2ed16fd8e4c8b660bb758b01fa32d826f29 Mon Sep 17 00:00:00 2001
From: Zhichao Cao <zhichao@fb.com>
Date: Wed, 3 Apr 2019 13:23:48 -0700
Subject: [PATCH] Fix the potential DB crash caused by call EndTrace before
 StartTrace (#5130)

Summary:
Although user should first call StartTrace to begin the RocksDB tracing function and call EndTrace to stop the tracing process, user can accidentally call EndTrace first. It will cause segment fault and crash the DB instance. The issue is fixed by checking the pointer first.

Test case added in db_test2.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5130

Differential Revision: D14691420

Pulled By: zhichao-cao

fbshipit-source-id: 3be13d2f944bc453728ef8eef67b68d7ad0939c8
---
 db/db_impl.cc  | 9 +++++++--
 db/db_test2.cc | 2 ++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/db/db_impl.cc b/db/db_impl.cc
index eeb1670de..4eb7091cb 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -3655,8 +3655,13 @@ Status DBImpl::StartTrace(const TraceOptions& trace_options,
 
 Status DBImpl::EndTrace() {
   InstrumentedMutexLock lock(&trace_mutex_);
-  Status s = tracer_->Close();
-  tracer_.reset();
+  Status s;
+  if (tracer_ != nullptr) {
+    s = tracer_->Close();
+    tracer_.reset();
+  } else {
+    return Status::IOError("No trace file to close");
+  }
   return s;
 }
 
diff --git a/db/db_test2.cc b/db/db_test2.cc
index 9a351dac0..dabb34fa9 100644
--- a/db/db_test2.cc
+++ b/db/db_test2.cc
@@ -2875,6 +2875,8 @@ TEST_F(DBTest2, TraceAndReplay) {
   Random rnd(301);
   Iterator* single_iter = nullptr;
 
+  ASSERT_TRUE(db_->EndTrace().IsIOError());
+
   std::string trace_filename = dbname_ + "/rocksdb.trace";
   std::unique_ptr<TraceWriter> trace_writer;
   ASSERT_OK(NewFileTraceWriter(env_, env_opts, trace_filename, &trace_writer));