Imported Upstream version 6.10.0.49

Former-commit-id: 1d6753294b2993e1fbf92de9366bb9544db4189b

external/llvm-project/compiler-rt/test/tsan/race_on_write.cc

@@ -0,0 +1,38 @@
+// RUN: %clangxx_tsan -O1 %s -o %t && %deflake %run %t | FileCheck %s
+#include "test.h"
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+int fd;
+char buf;
+
+void *Thread1(void *x) {
+  buf = 1;
+  barrier_wait(&barrier);
+  return NULL;
+}
+
+void *Thread2(void *x) {
+  write(fd, &buf, 1);
+  return NULL;
+}
+
+int main() {
+  barrier_init(&barrier, 2);
+  fd = open("/dev/null", O_WRONLY);
+  if (fd < 0) return 1;
+  pthread_t t[2];
+  pthread_create(&t[0], NULL, Thread1, NULL);
+  barrier_wait(&barrier);
+  pthread_create(&t[1], NULL, Thread2, NULL);
+  pthread_join(t[0], NULL);
+  pthread_join(t[1], NULL);
+  close(fd);
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK:   Read of size 1
+// CHECK:     #0 write
+// CHECK:   Previous write of size 1
+// CHECK:     #0 Thread1