linux-kernel - [PATCH 4.4 166/342] virtio_balloon: fix race by fill and leak

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Message-Id: <20160301234533.324490742@linuxfoundation.org>
Date:	Tue, 01 Mar 2016 23:54:39 +0000
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	<linux-kernel@...r.kernel.org>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<stable@...r.kernel.org>, Minchan Kim <minchan@...nel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: [PATCH 4.4 166/342] virtio_balloon: fix race by fill and leak

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

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

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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

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

--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -209,8 +209,8 @@ static unsigned leak_balloon(struct virt
 	 */
 	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;
 }