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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, "Michael S. Tsirkin" <mst@redhat.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        Michal Hocko <mhocko@suse.com>,
        Wei Wang <wei.w.wang@intel.com>,
        Jan Stancek <jstancek@redhat.com>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Subject: [PATCH 4.14 44/45] virtio_balloon: fix increment of vb->num_pfns in fill_balloon()
Date:   Thu, 11 Oct 2018 17:40:11 +0200
Message-Id: <20181011152510.855514157@linuxfoundation.org>
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4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Jan Stancek <jstancek@redhat.com>

commit d9e427f6ab8142d6868eb719e6a7851aafea56b6 upstream.

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>
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/virtio/virtio_balloon.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -174,13 +174,12 @@ static unsigned fill_balloon(struct virt
 	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;