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-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=403f24d3d51760a8b9368d595fa5f48c309f1a0f;p=linux-beck.git

rbd: protect read of snapshot sequence number

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>
---

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index a75fe93a25b1..5ab9f55d3e0c 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -1684,7 +1684,9 @@ 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: