Index: include/clang/Tooling/Tooling.h
===================================================================
--- include/clang/Tooling/Tooling.h
+++ include/clang/Tooling/Tooling.h
@@ -356,6 +356,11 @@
   /// append them to ASTs.
   int buildASTs(std::vector<std::unique_ptr<ASTUnit>> &ASTs);
 
+  /// Sets whether working directory should be restored after calling run(). By
+  /// default, working directory is restored. However, it could be useful to
+  /// turn this off when running on multiple threads to avoid the raciness.
+  void setRestoreWorkingDir(bool RestoreCWD);
+
   /// Returns the file manager used in the tool.
   ///
   /// The file manager is shared between all translation units.
@@ -380,6 +385,8 @@
   ArgumentsAdjuster ArgsAdjuster;
 
   DiagnosticConsumer *DiagConsumer = nullptr;
+
+  bool RestoreCWD = true;
 };
 
 template <typename T>
Index: lib/Tooling/AllTUsExecution.cpp
===================================================================
--- lib/Tooling/AllTUsExecution.cpp
+++ lib/Tooling/AllTUsExecution.cpp
@@ -104,7 +104,12 @@
   {
     llvm::ThreadPool Pool(ThreadCount == 0 ? llvm::hardware_concurrency()
                                            : ThreadCount);
-
+    llvm::SmallString<128> InitialWorkingDir;
+    if (auto EC = llvm::sys::fs::current_path(InitialWorkingDir)) {
+      InitialWorkingDir = "";
+      llvm::errs() << "Error while getting current working directory: "
+                   << EC.message() << "\n";
+    }
     for (std::string File : Files) {
       Pool.async(
           [&](std::string Path) {
@@ -116,12 +121,19 @@
             for (const auto &FileAndContent : OverlayFiles)
               Tool.mapVirtualFile(FileAndContent.first(),
                                   FileAndContent.second);
+            // Do not restore working dir from multiple threads to avoid races.
+            Tool.setRestoreWorkingDir(false);
             if (Tool.run(Action.first.get()))
               AppendError(llvm::Twine("Failed to run action on ") + Path +
                           "\n");
           },
           File);
     }
+    if (!InitialWorkingDir.empty()) {
+      if (auto EC = llvm::sys::fs::set_current_path(InitialWorkingDir))
+        llvm::errs() << "Error while restoring working directory: "
+                     << EC.message() << "\n";
+    }
   }
 
   if (!ErrorMsg.empty())
Index: lib/Tooling/Tooling.cpp
===================================================================
--- lib/Tooling/Tooling.cpp
+++ lib/Tooling/Tooling.cpp
@@ -441,6 +441,17 @@
     AbsolutePaths.push_back(std::move(*AbsPath));
   }
 
+  // Remember the working directory in case we need to restore it.
+  std::string InitialWorkingDir;
+  if (RestoreCWD) {
+    if (auto CWD = OverlayFileSystem->getCurrentWorkingDirectory()) {
+      InitialWorkingDir = std::move(*CWD);
+    } else {
+      llvm::errs() << "Could not get working directory: "
+                   << CWD.getError().message() << "\n";
+    }
+  }
+
   for (llvm::StringRef File : AbsolutePaths) {
     // Currently implementations of CompilationDatabase::getCompileCommands can
     // change the state of the file system (e.g.  prepare generated headers), so
@@ -508,6 +519,13 @@
       }
     }
   }
+
+  if (!InitialWorkingDir.empty()) {
+    if (auto EC =
+            OverlayFileSystem->setCurrentWorkingDirectory(InitialWorkingDir))
+      llvm::errs() << "Error when trying to restore working dir: "
+                   << EC.message() << "\n";
+  }
   return ProcessingFailed ? 1 : (FileSkipped ? 2 : 0);
 }
 
@@ -544,6 +562,10 @@
   return run(&Action);
 }
 
+void ClangTool::setRestoreWorkingDir(bool RestoreCWD) {
+  this->RestoreCWD = RestoreCWD;
+}
+
 namespace clang {
 namespace tooling {