Patch "virtio_balloon: fix race by fill and leak" has been added to the 4.4-stable tree

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

virtio_balloon: fix race by fill and leak

to the 4.4-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:
virtio_balloon-fix-race-by-fill-and-leak.patch
and it can be found in the queue-4.4 subdirectory.

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

From: Minchan Kim <[email protected]>
Date: Mon, 28 Dec 2015 08:35:12 +0900
Subject: virtio_balloon: fix race by fill and leak

From: Minchan Kim <[email protected]>

commit f68b992bbb474641881932c61c92dcfa6f5b3689 upstream.

During my compaction-related stuff, I encountered a bug with ballooning.

With repeated inflating and deflating cycle, guest memory( ie, cat /proc/meminfo | grep MemTotal) is decreased and couldn't be recovered.

The reason is balloon_lock doesn't cover release_pages_balloon so struct virtio_balloon fields could be overwritten by race of fill_balloon(e,g, vb->*pfns could be critical).

This patch fixes it in my test.

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

@@ -209,8 +209,8 @@ static unsigned leak_balloon(struct virt
 	 */
 	if (vb->num_pfns != 0)
 		tell_host(vb, vb->deflate_vq);
-	mutex_unlock(&vb->balloon_lock);
 	release_pages_balloon(vb);
+	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }
 

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

queue-4.4/virtio_balloon-fix-race-by-fill-and-leak.patch queue-4.4/virtio_balloon-fix-race-between-migration-and-ballooning.patch