Index: lib/tsan/rtl/tsan_interceptors.cc
===================================================================
--- lib/tsan/rtl/tsan_interceptors.cc
+++ lib/tsan/rtl/tsan_interceptors.cc
@@ -228,6 +228,16 @@
   libignore()->OnLibraryLoaded(0);
 }
 
+// The following two hooks can be used by for cooperative scheduling when
+// locking.
+#ifdef TSAN_EXTERNAL_HOOKS
+void OnPotentiallyBlockingRegionBegin();
+void OnPotentiallyBlockingRegionEnd();
+#else
+SANITIZER_WEAK_CXX_DEFAULT_IMPL void OnPotentiallyBlockingRegionBegin() {}
+SANITIZER_WEAK_CXX_DEFAULT_IMPL void OnPotentiallyBlockingRegionEnd() {}
+#endif
+
 }  // namespace __tsan
 
 static ThreadSignalContext *SigCtx(ThreadState *thr) {
@@ -866,6 +876,8 @@
 // Used in thread-safe function static initialization.
 STDCXX_INTERCEPTOR(int, __cxa_guard_acquire, atomic_uint32_t *g) {
   SCOPED_INTERCEPTOR_RAW(__cxa_guard_acquire, g);
+  OnPotentiallyBlockingRegionBegin();
+  auto on_exit = at_scope_exit(&OnPotentiallyBlockingRegionEnd);
   for (;;) {
     u32 cmp = atomic_load(g, memory_order_acquire);
     if (cmp == 0) {
Index: test/tsan/cxa_guard_acquire.cc
===================================================================
--- test/tsan/cxa_guard_acquire.cc
+++ test/tsan/cxa_guard_acquire.cc
@@ -0,0 +1,25 @@
+// RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+
+#include <stdio.h>
+
+namespace __tsan {
+
+void OnPotentiallyBlockingRegionBegin() {
+  printf("Enter __cxa_guard_acquire\n");
+}
+
+void OnPotentiallyBlockingRegionEnd() { printf("Exit __cxa_guard_acquire\n"); }
+
+} // namespace __tsan
+
+int main(int argc, char **argv) {
+  // CHECK: Enter main
+  printf("Enter main\n");
+  // CHECK-NEXT: Enter __cxa_guard_acquire
+  // CHECK-NEXT: Exit __cxa_guard_acquire
+  static int s = argc;
+  (void)s;
+  // CHECK-NEXT: Exit main
+  printf("Exit main\n");
+  return 0;
+}