virtio_balloon: fix increment of vb->num_pfns in fill_balloon()

commit c7cdff0e8647 ("virtio_balloon: fix deadlock on OOM")
changed code to increment vb->num_pfns before call to
set_page_pfns(), which used to happen only after.

This patch fixes boot hang for me on ppc64le KVM guests.

Fixes: c7cdff0e8647 ("virtio_balloon: fix deadlock on OOM")
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Wei Wang <wei.w.wang@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 1 insertions, 2 deletions

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 7960746f7597..a1fb52cb3f0a 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -174,13 +174,12 @@ static unsigned fill_balloon(struct virtio_balloon *vb, size_t num)
         while ((page = balloon_page_pop(&pages))) {
                 balloon_page_enqueue(&vb->vb_dev_info, page);
 
-                vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
-
                 set_page_pfns(vb, vb->pfns + vb->num_pfns, page);
                 vb->num_pages += VIRTIO_BALLOON_PAGES_PER_PAGE;
                 if (!virtio_has_feature(vb->vdev,
                                         VIRTIO_BALLOON_F_DEFLATE_ON_OOM))
                         adjust_managed_page_count(page, -1);
+                vb->num_pfns += VIRTIO_BALLOON_PAGES_PER_PAGE;
         }
 
         num_allocated_pages = vb->num_pfns;