Fix setjmp.bug_152210274 with HWASan/stack MTE enabled.

This test was flaky because there was no synchronization between the end
of the test function scope and the jumper threads, resulting in a racy
use-after-scope when accessing the thread array. Fix it by joining the
threads before leaving the test function scope.

Replace the thread array access, which can race with the store to the
thread array in the main thread, with an access to a pre-initialized
variable, which acts as a kind of enforcement that the threads are done
before leaving the test.

Bug: 227390656
Change-Id: Icfbb0d7cae66c12e5ce31072c34529e3c5fdf563

tests/setjmp_test.cpp

@@ -278,7 +278,6 @@ TEST(setjmp, setjmp_stack) {
 }
 
 TEST(setjmp, bug_152210274) {
-  SKIP_WITH_HWASAN; // b/227390656
   // Ensure that we never have a mangled value in the stack pointer.
 #if defined(__BIONIC__)
   struct sigaction sa = {.sa_flags = SA_SIGINFO, .sa_sigaction = [](int, siginfo_t*, void*) {}};
@@ -299,15 +298,19 @@ TEST(setjmp, bug_152210274) {
         perror("setjmp");
         abort();
       }
-      if (*static_cast<pid_t*>(arg) == 100) longjmp(buf, 1);
+      // This will never be true, but the compiler doesn't know that, so the
+      // setjmp won't be removed by DCE. With HWASan/MTE this also acts as a
+      // kind of enforcement that the threads are done before leaving the test.
+      if (*static_cast<size_t*>(arg) != 123) longjmp(buf, 1);
     }
     return nullptr;
   };
+  pthread_t threads[kNumThreads];
   pid_t tids[kNumThreads] = {};
+  size_t var = 123;
   for (size_t i = 0; i < kNumThreads; ++i) {
-    pthread_t t;
-    ASSERT_EQ(0, pthread_create(&t, nullptr, jumper, &tids[i]));
-    tids[i] = pthread_gettid_np(t);
+    ASSERT_EQ(0, pthread_create(&threads[i], nullptr, jumper, &var));
+    tids[i] = pthread_gettid_np(threads[i]);
   }
 
   // Start the interrupter thread.
@@ -327,6 +330,9 @@ TEST(setjmp, bug_152210274) {
   pthread_t t;
   ASSERT_EQ(0, pthread_create(&t, nullptr, interrupter, tids));
   pthread_join(t, nullptr);
+  for (size_t i = 0; i < kNumThreads; i++) {
+    pthread_join(threads[i], nullptr);
+  }
 #else
   GTEST_SKIP() << "tests uses functions not in glibc";
 #endif