linux-kernel - [PATCH 1/2] virtio_balloon: fix race by fill and leak

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Date:	Mon, 28 Dec 2015 08:35:12 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Michael S. Tsirkin" <mst@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Rafael Aquini <aquini@...hat.com>,
	Minchan Kim <minchan@...nel.org>, <stable@...r.kernel.org>
Subject: [PATCH 1/2] virtio_balloon: fix race by fill and leak

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.

Cc: <stable@...r.kernel.org>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 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 7efc32945810..7d3e5d0e9aa4 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -209,8 +209,8 @@ 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_balloon(vb);
+	mutex_unlock(&vb->balloon_lock);
 	return num_freed_pages;
 }
 
-- 
1.9.1

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