Patch "balloon: check the number of available pages in leak balloon" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

balloon: check the number of available pages in leak balloon

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
balloon-check-the-number-of-available-pages-in-leak-balloon.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Konstantin Neumoin <[email protected]>
Date: Mon, 11 Jul 2016 15:28:59 +0300
Subject: balloon: check the number of available pages in leak balloon

From: Konstantin Neumoin <[email protected]>

commit 37cf99e08c6fb4dcea0f9ad2b13b6daa8c76a711 upstream.

The balloon has a special mechanism that is subscribed to the oom notification which leads to deflation for a fixed number of pages. The number is always fixed even when the balloon is fully deflated. But leak_balloon did not expect that the pages to deflate will be more than taken, and raise a "BUG" in balloon_page_dequeue when page list will be empty.

So, the simplest solution would be to check that the number of releases pages is less or equal to the number taken pages.

---
 drivers/virtio/virtio_balloon.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -202,6 +202,8 @@ static unsigned leak_balloon(struct virt
 	num = min(num, ARRAY_SIZE(vb->pfns));
 
 	mutex_lock(&vb->balloon_lock);
+	/* We can't release more pages than taken */
+	num = min(num, (size_t)vb->num_pages);
 	for (vb->num_pfns = 0; vb->num_pfns < num;
 	     vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE) {
 		page = balloon_page_dequeue(vb_dev_info);

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/balloon-check-the-number-of-available-pages-in-leak-balloon.patch