From: Vegard Nossum <vegard.nossum@oracle.com>
Date: Thu, 5 Sep 2013 11:00:14 +0000 (+0200)
Subject: xen/blkback: fix reference counting
X-Git-Url: http://git.mmlx.us/?a=commitdiff_plain;h=d0ac18ce1a3d607ad650fd4b9d371be75a5c8e3a;p=linux-edison.git

xen/blkback: fix reference counting

commit ea5ec76d76da9279d12027c1828544c5ccbe7932 upstream.

If the permission check fails, we drop a reference to the blkif without
having taken it in the first place. The bug was introduced in commit
604c499cbbcc3d5fe5fb8d53306aa0fae1990109 (xen/blkback: Check device
permissions before allowing OP_DISCARD).

Cc: Jan Beulich <JBeulich@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index d81dfca755d..03dd4aa612d 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -649,6 +649,8 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
 	unsigned long secure;
 	struct phys_req preq;
 
+	xen_blkif_get(blkif);
+
 	preq.sector_number = req->u.discard.sector_number;
 	preq.nr_sects      = req->u.discard.nr_sectors;
 
@@ -661,7 +663,6 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
 	}
 	blkif->st_ds_req++;
 
-	xen_blkif_get(blkif);
 	secure = (blkif->vbd.discard_secure &&
 		 (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
 		 BLKDEV_DISCARD_SECURE : 0;