linux-kernel - [PATCH 3.19.y-ckt 095/210] virtio_balloon: fix race by fill and leak

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Message-Id: <1454030348-17736-96-git-send-email-kamal@canonical.com>
Date:	Thu, 28 Jan 2016 17:17:13 -0800
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Minchan Kim <minchan@...nel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 095/210] virtio_balloon: fix race by fill and leak

3.19.8-ckt14 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Minchan Kim <minchan@...nel.org>

commit f68b992bbb474641881932c61c92dcfa6f5b3689 upstream.

During my compaction-related stuff, I encountered a bug
with ballooning.

With repeated inflating and deflating cycle, guest memory(
ie, cat /proc/meminfo | grep MemTotal) is decreased and
couldn't be recovered.

The reason is balloon_lock doesn't cover release_pages_balloon
so struct virtio_balloon fields could be overwritten by race
of fill_balloon(e,g, vb->*pfns could be critical).

This patch fixes it in my test.

Signed-off-by: Minchan Kim <minchan@...nel.org>
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
Signed-off-by: Kamal Mostafa <kamal@...onical.com>
---
 drivers/virtio/virtio_balloon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index b8b7a6c..803f794 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -206,8 +206,8 @@ static unsigned leak_balloon(struct virtio_balloon *vb, size_t num)
 	 */
 	if (vb->num_pfns != 0)
 		tell_host(vb, vb->deflate_vq);
-	mutex_unlock(&vb->balloon_lock);
 	release_pages_by_pfn(vb->pfns, vb->num_pfns);
+	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }
 
-- 
1.9.1