Re: [PATCH 4/6] coroutine-lock: reimplement CoRwLock to fix downgrade bug

[Paolo Bonzini]

On 17/03/21 16:17, David Edmondson wrote:
> > +    if (tkt) {
> > +        if (tkt->read) {
> > +            if (lock->owners >= 0) {
> > +                lock->owners++;
> > +                co = tkt->co;
> > +            }
> > +        } else {
> > +            if (lock->owners == 0) {
> > +                lock->owners = -1;
> > +                co = tkt->co;
> > +            }
> > +        }
> > +    }
> > +
> > +    if (co) {
> > +        QSIMPLEQ_REMOVE_HEAD(&lock->tickets, next);
> > +        qemu_co_mutex_unlock(&lock->mutex);
> > +        aio_co_wake(co);
> > +    } else {
> > +        qemu_co_mutex_unlock(&lock->mutex);
> > +    }
>
> This block could be pushed up into the earlier block, but I imagine that
> the compiler will do it for you.

I guess I could do

    if (!tkt || (tkt->read ? lock->owners < 0 : lock->owners != 0)) {
        qemu_co_mutex_unlock(&lock->mutex);
        return;
    }
    if (tkt->read) {
        lock->owners++;
    } else {
        lock->owners = -1;
    }

    co = tkt->co;
    QSIMPLEQ_REMOVE_HEAD(&lock->tickets, next);
    qemu_co_mutex_unlock(&lock->mutex);
    aio_co_wake(co);

but I find it less readable.  So that leaves only the of/or typo, right?

Paolo