Re: [KVM PATCH v10] kvm: add support for irqfd

Michael S. Tsirkin
2009-06-11T13:36:55Z

On Thu, Jun 11, 2009 at 04:16:47PM +0300, Michael S. Tsirkin wrote:
> > +
> > + ret = file->f_op->poll(file, &irqfd->pt);
> > + if (ret < 0)
> > + goto fail;

Looking at it some more, we have:
struct file_operations {
....
unsigned int (*poll) (struct file *, struct poll_table_struct *);

So the comparison above does not seem to make sense:
it seems that the return value from poll can not be negative.

Will the callback be executed if someone did a write to eventfd
before we attached it? If no, maybe we should call it here
if ret != 0.

> > +
> > + irqfd->file = file;
> > +
> > + mutex_lock(&kvm->lock);
> > + list_add_tail(&irqfd->list, &kvm->irqfds);
> > + mutex_unlock(&kvm->lock);
> > +
> > + return 0;
> > +
> > +fail:
> > + if (irqfd->wqh)
> > + remove_wait_queue(irqfd->wqh, &irqfd->wait);
>
> Why are these 2 lines here? Either we might get a callback even though
> poll failed - and then this test without lock is probably racy -
> or we can't, and then we can replace the above with BUG_ON(irqfd->wqh).
>
> Which is it? I think the later ...
>
>
> > +
> > + if (file && !IS_ERR(file))
> > + fput(file);
> > +
> > + kfree(irqfd);
> > + return ret;
> > +}
> > +