[Devel] [PATCH RHEL7 COMMIT] ms/balloon: check the number of available pages in leak balloon

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-514.vz7.27.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-514.vz7.27.10
------>
commit 613d186f9eada152a90f300aa1dc31ac37e0ed8c
Author: Konstantin Neumoin <kneumoin at virtuozzo.com>
Date:   Mon Jan 16 20:21:30 2017 +0400

    ms/balloon: check the number of available pages in leak balloon
    
    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.
    
    Cc: stable at vger.kernel.org
    Signed-off-by: Konstantin Neumoin <kneumoin at virtuozzo.com>
    Signed-off-by: Denis V. Lunev <den at openvz.org>
    CC: Michael S. Tsirkin <mst at redhat.com>
    Signed-off-by: Michael S. Tsirkin <mst at redhat.com>
    
    https://jira.sw.ru/browse/PSBM-58601
    
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 drivers/virtio/virtio_balloon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index e97329d..a9ca908 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -196,6 +196,8 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 	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);