balloon: check the number of available pages in leak balloon

[ Upstream commit 37cf99e08c6fb4dcea0f9ad2b13b6daa8c76a711 ]

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@vger.kernel.org
Signed-off-by: Konstantin Neumoin <kneumoin@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 440d78f39c01f1f050b8cc245fa33d50d03fc5cd..0f9638e72b9123a5abca84a2e079d3592eaebf1a 100644 (file)
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -178,6 +178,8 @@ static void 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);