turnstile fixes

lib/mutex.c

@@ -68,6 +68,8 @@ static void mutex_lock_slow(mutex_t* mutex, uintptr_t self) {
         // Before the scheduler is up, nobody can be preempted while holding a lock. Just keep spinning.
         if (self == MUTEX_ANON_OWNER || owner == MUTEX_ANON_OWNER) {
             spins = 0;
+            arch_cpu_pause();
+            word = atomic_load(mutex, ATOMIC_RELAXED);
             continue;
         }