From 2f089cb89d2f47702c31bd584c12badc88bbe17c Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sat, 9 Nov 2013 13:36:09 -0200
Subject: [PATCH] block: xen-blkfront: Fix possible NULL ptr dereference

In the blkif_release function the bdget_disk() call might returns
a NULL ptr which might be dereferenced on bdev->bd_openers checking

Signed-off-by: Felipe Pena <felipensp@gmail.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
[v2: Added WARN per Roger's suggestion]
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