On Mon, 13 Aug 2012 11:41:23 +0300, "Michael S. Tsirkin" [off-list ref] wrote:

On Fri, Aug 10, 2012 at 02:55:15PM -0300, Rafael Aquini wrote:

quoted

+/*
+ * 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.

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