Index: llvm/lib/Support/Windows/Signals.inc
===================================================================
--- llvm/lib/Support/Windows/Signals.inc
+++ llvm/lib/Support/Windows/Signals.inc
@@ -731,6 +731,11 @@
 /// otherwise.
 static std::error_code WINAPI
 WriteWindowsDumpFile(PMINIDUMP_EXCEPTION_INFORMATION ExceptionInfo) {
+  struct ScopedCriticalSection {
+    ScopedCriticalSection() { EnterCriticalSection(&CriticalSection); }
+    ~ScopedCriticalSection() { LeaveCriticalSection(&CriticalSection); }
+  } SCS;
+
   using namespace llvm;
   using namespace llvm::sys;
 
Index: llvm/unittests/Support/CMakeLists.txt
===================================================================
--- llvm/unittests/Support/CMakeLists.txt
+++ llvm/unittests/Support/CMakeLists.txt
@@ -94,6 +94,7 @@
   UnicodeTest.cpp
   VersionTupleTest.cpp
   VirtualFileSystemTest.cpp
+  WindowsDumpFileTest.cpp
   WithColorTest.cpp
   YAMLIOTest.cpp
   YAMLParserTest.cpp
Index: llvm/unittests/Support/WindowsDumpFileTest.cpp
===================================================================
--- /dev/null
+++ llvm/unittests/Support/WindowsDumpFileTest.cpp
@@ -0,0 +1,112 @@
+//===- llvm/unittests/Support/WindowsDumpFileTest.cpp ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Signals.h"
+
+#include "llvm/Config/config.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Process.h"
+#include "llvm/Support/Program.h"
+#include "llvm/Support/Threading.h"
+
+#include "gtest/gtest.h"
+
+#include <atomic>
+#include <future>
+
+#if defined(_WIN32) && LLVM_ENABLE_THREADS && LLVM_ENABLE_CRASH_DUMPS
+
+using namespace llvm;
+
+// See llvm/utils/unittest/UnitTestMain/TestMain.cpp.
+extern const char *TestMainArgv0;
+
+// Just a reachable symbol to ease resolving of the executable's path.
+static cl::opt<std::string>
+    WindowsDumpFileTestStringArg1("windows-dump-file-test-string-arg1");
+
+TEST(WindowsDumpFileTest, MultiThread) {
+  unsigned NumThreads = hardware_concurrency().compute_thread_count();
+  if (NumThreads == 1)
+    GTEST_SKIP();
+
+  // Use at least 4 threads.
+  NumThreads = std::max(NumThreads, 4U);
+
+  if (getenv("LLVM_WINDOWS_DUMP_FILE_TEST_MULTI_THREAD")) {
+    ASSERT_FALSE(sys::Process::AreCoreFilesPrevented());
+    sys::PrintStackTraceOnErrorSignal(StringRef(), false);
+    ASSERT_FALSE(sys::Process::AreCoreFilesPrevented());
+
+    std::vector<std::thread> Threads;
+    std::atomic<unsigned> ThreadsStarted(0);
+    std::promise<void> Started;
+    std::mutex Mutex;
+    std::condition_variable Cond;
+    std::atomic<bool> Ready(false);
+    for (unsigned I = 0; I < NumThreads; ++I)
+      Threads.emplace_back([&, NumThreads] {
+        if (++ThreadsStarted == NumThreads)
+          Started.set_value();
+
+        std::unique_lock<std::mutex> Lock(Mutex);
+        Cond.wait(Lock, [&] { return Ready.load(); });
+        Lock.unlock();
+
+        LLVM_BUILTIN_TRAP;
+      });
+
+    Started.get_future().wait();
+
+    {
+      std::unique_lock<std::mutex> Lock(Mutex);
+      Ready = true;
+    }
+    Cond.notify_all();
+
+    for (auto &T : Threads)
+      T.join();
+
+    LLVM_BUILTIN_TRAP;
+  }
+
+  // Create a temporary directory to be used as the temporary directory for the
+  // test run.
+  SmallString<128> TmpDir;
+  std::error_code EC =
+      sys::fs::createUniqueDirectory("WindowsDumpFileTest", TmpDir);
+  ASSERT_FALSE(EC);
+
+  std::string Executable =
+      sys::fs::getMainExecutable(TestMainArgv0, &WindowsDumpFileTestStringArg1);
+  StringRef Argv[] = {Executable,
+                      "--gtest_filter=WindowsDumpFileTest.MultiThread"};
+  std::vector<StringRef> Env;
+  Env.emplace_back("LLVM_WINDOWS_DUMP_FILE_TEST_MULTI_THREAD=1");
+
+  // Set temporary directory environment variables.
+  std::string TmpEnv = ("TMP=" + TmpDir).str();
+  Env.emplace_back(TmpEnv);
+  std::string TempEnv = ("TEMP=" + TmpDir).str();
+  Env.emplace_back(TempEnv);
+
+  // The following is required to prevent disabling of dumps.
+  Env.emplace_back("LLVM_PROGRAM_TEST_NO_STACKTRACE_HANDLER=1");
+
+  unsigned TimeoutInSecs = NumThreads;
+  std::string Error;
+  int Ret = sys::ExecuteAndWait(Executable, Argv, ArrayRef<StringRef>(Env), {},
+                                TimeoutInSecs, 0, &Error);
+  ASSERT_NE(Ret, 0);
+  ASSERT_TRUE(Error.empty());
+
+  // Remove temporary directory.
+  sys::fs::remove_directories(TmpDir);
+}
+
+#endif