Broken mutex

[lecopzer]

HI,
https://github.com/PikoRT/pikoRT/blob/master/kernel/mutex.c#L14

int sys_pthread_mutex_lock(kernel_mutex_t *mutex)
{
    mutex->val++;
    if (!mutex->val)
        return 0;

I'm pretty sure such code is not mutual exclusion.
It better to implement cmpxchg by ldrex or ldxr

Also, the tests for mutext_* are not test for mutual exclusion at all, they only test for the functions finish execution or not.