Futex wait is not interrupted by signals if no timeout is provided

[Elijah Stone]

I've observed a strange behaviour of futexes that I believe to be a bug.  If a 
signal is delivered while a futex wait is in progress, the wait will be 
interrupted, but only if that wait had a timeout.  I expect it to be 
interrupted regardless of whether a timeout is provided.  The following 
runnable snippet demonstrates this:

void handler(int) { printf("SIGINT\n"); }
int main() {
	signal(SIGINT,handler);
	int i=2;
	printf("1\n");
	syscall(SYS_futex, &i, FUTEX_WAIT, 2, &(struct timespec){.tv_sec=1000});
	printf("2\n");
	syscall(SYS_futex, &i, FUTEX_WAIT, 2, NULL);
	printf("3\n");
}

Pressing ^C once causes the first wait to terminate, and '2' to be printed. 
But repeatedly pressing it after that does not allow the program to make 
progress.