From: Josh Durgin <josh.durgin@dreamhost.com>
Date: Mon, 5 Dec 2011 18:47:13 +0000 (-0800)
Subject: rbd: protect read of snapshot sequence number
X-Git-Tag: v3.4.20~84
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=45739514727c294e843269d515b952d5dbd911bf;p=platform%2Fkernel%2Flinux-stable.git

rbd: protect read of snapshot sequence number

(cherry picked from commit 403f24d3d51760a8b9368d595fa5f48c309f1a0f)

This is updated whenever a snapshot is added or deleted, and the
snapc pointer is changed with every refresh of the header.

Signed-off-by: Josh Durgin <josh.durgin@dreamhost.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>
Reviewed-by: Yehuda Sadeh <yehuda@hq.newdream.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index c1f7701..ff224ba 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1683,7 +1683,9 @@ static int rbd_header_add_snap(struct rbd_device *dev,
 	if (ret < 0)
 		return ret;
 
-	dev->header.snapc->seq =  new_snapid;
+	down_write(&dev->header_rwsem);
+	dev->header.snapc->seq = new_snapid;
+	up_write(&dev->header_rwsem);
 
 	return 0;
 bad: