tsan: disable trace switching after multithreaded fork

The problem is reported in:
google/sanitizers#945

We already disable as much as possible after multithreaded fork,
trace switching is last place that can hang due to basic
operations (memory accesses, function calls).
Disable it too.



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@331163 91177308-0d34-0410-b5e6-96231b3b80d8

Author: dvyukov

lib/tsan/rtl/tsan_rtl.cc

@@ -547,6 +547,10 @@ u32 CurrentStackId(ThreadState *thr, uptr pc) {
 }
 
 void TraceSwitch(ThreadState *thr) {
+#if !SANITIZER_GO
+  if (ctx->after_multithreaded_fork)
+    return;
+#endif
   thr->nomalloc++;
   Trace *thr_trace = ThreadTrace(thr->tid);
   Lock l(&thr_trace->mtx);

lib/tsan/rtl/tsan_rtl.h

@@ -520,7 +520,9 @@ struct Context {
   Context();
 
   bool initialized;
+#if !SANITIZER_GO
   bool after_multithreaded_fork;
+#endif
 
   MetaMap metamap;