linux-kernel - [PATCH] virtio_balloon: fix increment of vb->num_pfns in fill

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Message-Id: <65e5cdb45d2532f9b99e2f412d9169322f778239.1512121454.git.jstancek@redhat.com>
Date:   Fri,  1 Dec 2017 10:50:28 +0100
From:   Jan Stancek <jstancek@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com,
        virtualization@...ts.linux-foundation.org
Cc:     linux-kernel@...r.kernel.org, jstancek@...hat.com,
        penguin-kernel@...ove.SAKURA.ne.jp, mhocko@...e.com,
        wei.w.wang@...el.com
Subject: [PATCH] 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@...hat.com>
Cc: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Wei Wang <wei.w.wang@...el.com>
Signed-off-by: Jan Stancek <jstancek@...hat.com>
---
 drivers/virtio/virtio_balloon.c | 3 +--
 1 file changed, 1 insertion(+), 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;
-- 
1.8.3.1