Re: [Qemu-devel] [PATCH 2/3] Make paio subsystem use threadlets

[Anthony Liguori]

On 10/20/2010 04:30 AM, Stefan Hajnoczi wrote:
> >      } else if (acb->ret == -EINPROGRESS) {
> >          active = 1;
> >      }
> > -    mutex_unlock(&lock);
> >
> >      if (active) {
> >          /* fail safe: if the aio could not be canceled, we wait for
> >      
> while (qemu_paio_error(acb) == EINPROGRESS)
>      ;
>
> Tight loop with no memory barrier reading a memory location that is
> updated by another thread.  We shouldn't communicate between threads
> without barriers.
>    

We shouldn't use a tight loop period.  A condition should be used if 
signalling is needed.

And we shouldn't rely on atomic assignments to communicate between 
threads.  Just use a mutex and avoid being fancier than we need to be.

Regards,

Anthony Liguori

> Stefan
>
>