--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/compiler-rt/test/tsan/fd_dup_norace2.cpp	Thu Feb 13 15:10:13 2020 +0900
@@ -0,0 +1,60 @@
+// RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+#include "test.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+
+// dup2(oldfd, newfd) races with read(newfd).
+// This is not reported as race because:
+// 1. Some software dups a closed pipe in place of a socket before closing
+//    the socket (to prevent races actually).
+// 2. Some daemons dup /dev/null in place of stdin/stdout.
+
+int fd;
+
+void *Thread(void *x) {
+  char buf;
+  int n = read(fd, &buf, 1);
+  if (n != 1) {
+    // This read can "legitimately" fail regadless of the fact that glibc claims
+    // that "there is no instant in the middle of calling dup2 at which new is
+    // closed and not yet a duplicate of old". Strace of the failing runs
+    // looks as follows:
+    //
+    //    [pid 122196] open("/dev/urandom", O_RDONLY) = 3
+    //    [pid 122196] open("/dev/urandom", O_RDONLY) = 4
+    //    Process 122382 attached
+    //    [pid 122382] read(3,  <unfinished ...>
+    //    [pid 122196] dup2(4, 3 <unfinished ...>
+    //    [pid 122382] <... read resumed> 0x7fcd139960b7, 1) = -1 EBADF (Bad file descriptor)
+    //    [pid 122196] <... dup2 resumed> )       = 3
+    //    read failed: n=-1 errno=9
+    //
+    // The failing read does not interfere with what this test tests,
+    // so we just ignore the failure.
+    //
+    // exit(printf("read failed: n=%d errno=%d\n", n, errno));
+  }
+  return 0;
+}
+
+int main() {
+  fd = open("/dev/urandom", O_RDONLY);
+  int fd2 = open("/dev/urandom", O_RDONLY);
+  if (fd == -1 || fd2 == -1)
+    exit(printf("open failed\n"));
+  pthread_t th;
+  pthread_create(&th, 0, Thread, 0);
+  if (dup2(fd2, fd) == -1)
+    exit(printf("dup2 failed\n"));
+  pthread_join(th, 0);
+  if (close(fd) == -1)
+    exit(printf("close failed\n"));
+  if (close(fd2) == -1)
+    exit(printf("close failed\n"));
+  fprintf(stderr, "DONE\n");
+}
+
+// CHECK-NOT: WARNING: ThreadSanitizer: data race
+// CHECK: DONE