Re: [PATCH v7 2/4] virtio_balloon: introduce migration primitives to balloon pages

[Rusty Russell]

On Mon, 13 Aug 2012 11:41:23 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> On Fri, Aug 10, 2012 at 02:55:15PM -0300, Rafael Aquini wrote:
> > +/*
> > + * Populate balloon_mapping->a_ops->freepage method to help compaction on
> > + * re-inserting an isolated page into the balloon page list.
> > + */
> > +void virtballoon_putbackpage(struct page *page)
> > +{
> > +	spin_lock(&pages_lock);
> > +	list_add(&page->lru, &vb_ptr->pages);
> > +	spin_unlock(&pages_lock);
> 
> Could the following race trigger:
> migration happens while module unloading is in progress,
> module goes away between here and when the function
> returns, then code for this function gets overwritten?
> If yes we need locking external to module to prevent this.
> Maybe add a spinlock to struct address_space?

The balloon module cannot be unloaded until it has leaked all its pages,
so I think this is safe:

        static void remove_common(struct virtio_balloon *vb)
        {
        	/* There might be pages left in the balloon: free them. */
        	while (vb->num_pages)
        		leak_balloon(vb, vb->num_pages);

Cheers,
Rusty.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/