Re: [syzbot] [kvm?] [net?] [virt?] general protection fault in vhost_work_queue

[Stefano Garzarella]

On Tue, May 30, 2023 at 11:01:11AM -0500, Mike Christie wrote:
> On 5/30/23 10:58 AM, Mike Christie wrote:
> > On 5/30/23 8:44 AM, Stefano Garzarella wrote:
> > > From a first glance, it looks like an issue when we call vhost_work_queue().
> > > @Mike, does that ring any bells since you recently looked at that code?
> >
> > I see the bug. needed to have set the dev->worker after setting worker->vtsk

Yes, I came to the same conclusion (see my email sent at the same time
:-).

> > like below:
> >
> >
> > diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > index a92af08e7864..7bd95984a501 100644
> > --- a/drivers/vhost/vhost.c
> > +++ b/drivers/vhost/vhost.c
> > @@ -564,7 +564,6 @@ static int vhost_worker_create(struct vhost_dev *dev)
> >  	if (!worker)
> >  		return -ENOMEM;
> >
> > -	dev->worker = worker;
> >  	worker->kcov_handle = kcov_common_handle();
> >  	init_llist_head(&worker->work_list);
> >  	snprintf(name, sizeof(name), "vhost-%d", current->pid);
> > @@ -576,6 +575,7 @@ static int vhost_worker_create(struct vhost_dev *dev)
> >  	}
> >
> >  	worker->vtsk = vtsk;
>
> Shoot, oh wait, I think I needed a smp_wmb to always make sure worker->vtask
> is set before dev->worker or vhost_work_queue could still end up seeing
> dev->worker set before worker->vtsk right?

But should we pair smp_wmb() with an smp_rmb() wherever we check 
dev->worker?

Thanks,
Stefano