thread_pthread: retry timer thread creation w/o attr on EINVAL

Setting a small stack size can fail due to having 3rd-party
libraries (e.g. libkqueue) loaded, if those libraries use
thread-local-storage (__thread) heavily.  This causes
pthread_create to fail with small stacks; even if our
timer_thread function does not hit any of the TLS-using code
paths.

Today, some RubyGems are capable of using libkqueue (or __thread
storage directly), and future versions of Ruby may use kqueue
internally.

cf. https://www.akkadia.org/drepper/tls.pdf

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58874 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_pthread.c

@@ -1587,6 +1587,7 @@ rb_thread_create_timer_thread(void)
 	int err;
 #ifdef HAVE_PTHREAD_ATTR_INIT
 	pthread_attr_t attr;
+	rb_vm_t *vm = GET_VM();
 
 	err = pthread_attr_init(&attr);
 	if (err != 0) {
@@ -1623,10 +1624,20 @@ rb_thread_create_timer_thread(void)
 	    rb_bug("rb_thread_create_timer_thread: Timer thread was already created\n");
 	}
 #ifdef HAVE_PTHREAD_ATTR_INIT
-	err = pthread_create(&timer_thread.id, &attr, thread_timer, &GET_VM()->gvl);
+	err = pthread_create(&timer_thread.id, &attr, thread_timer, &vm->gvl);
 	pthread_attr_destroy(&attr);
+
+	if (err == EINVAL) {
+	    /*
+	     * Even if we are careful with our own stack use in thread_timer(),
+	     * any third-party libraries (eg libkqueue) which rely on __thread
+	     * storage can cause small stack sizes to fail.  So lets hope the
+	     * default stack size is enough for them:
+	     */
+	    err = pthread_create(&timer_thread.id, NULL, thread_timer, &vm->gvl);
+	}
 #else
-	err = pthread_create(&timer_thread.id, NULL, thread_timer, &GET_VM()->gvl);
+	err = pthread_create(&timer_thread.id, NULL, thread_timer, &vm->gvl);
 #endif
 	if (err != 0) {
 	    rb_warn("pthread_create failed for timer: %s, scheduling broken",