The sigsuspend() system call gets interrupted when
another process attaches itself via ptrace.

How-To-Repeat: #include
<unistd.h>

int main(void)
{
        pause();
        return 0;
}
 
$ ./a.out &
$ truss -p `pgrep a.out`
process exit, rval = 0  
[1]   Done                    ./a.out
$