Re: [Qemu-devel] [PATCH v2 11/11] block: Only poll block layer fds in bdrv_aio_poll

[Fam Zheng <famz@redhat.com>]

On Wed, 07/29 09:37, Paolo Bonzini wrote:
> 
> 
> On 29/07/2015 06:42, Fam Zheng wrote:
> > @@ -2613,6 +2613,8 @@ bool bdrv_aio_poll(AioContext *ctx, bool blocking)
> >  {
> >      bool ret;
> >  
> > +    aio_disable_clients(ctx, AIO_CLIENT_DATAPLANE | AIO_CLIENT_NBD_SERVER);
> >      ret = aio_poll(ctx, blocking);
> > +    aio_enable_clients(ctx, AIO_CLIENT_DATAPLANE | AIO_CLIENT_NBD_SERVER);
> >      return ret;
> 
> This is not enough, because another thread's aio_poll can sneak in
> between calls to bdrv_aio_poll if the AioContext lock is released, and
> they will use the full set of clients.
> 
> Similar to your v1, it works with the large critical sections we
> currently have, but it has the same problem in the longer term.

Can we add more disable/enable pairs around bdrv_drain on top?

Fam

> 
> The clients have to be disabled around calls to bdrv_drain, as you were
> doing when you had pause/resume notifiers.  Patches 1-8 however are ok.
> 
> Paolo
>