>From 3fa80e3f14fb78eff6e5b0788f048b4a0c595c32 Mon Sep 17 00:00:00 2001
From: Steven Whitehouse <swhiteho@redhat.com>
Date: Mon, 23 Aug 2010 11:49:34 +0100
Subject: [PATCH 4/6] GFS2: Add a bug trap in allocation code

This adds a check to ensure that if we reach the block allocator
that we don't try and proceed if there is no alloc structure
hanging off the inode. This should only happen if there is a bug
in GFS2. The error return code is distinctive in order that it
will be easily spotted.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

diff --git a/fs/gfs2/rgrp.c b/fs/gfs2/rgrp.c
index 370c29b..66b6d4d 100644
--- a/fs/gfs2/rgrp.c
+++ b/fs/gfs2/rgrp.c
@@ -1496,11 +1496,19 @@ int gfs2_alloc_block(struct gfs2_inode *ip, u64 *bn, unsigned int *n)
struct gfs2_sbd *sdp = GFS2_SB(&ip->i_inode);
struct buffer_head *dibh;
struct gfs2_alloc *al = ip->i_alloc;
- struct gfs2_rgrpd *rgd = al->al_rgd;
+ struct gfs2_rgrpd *rgd;
u32 goal, blk;
u64 block;
int error;

+ /* Only happens if there is a bug in gfs2, return something distinctive
+ * to ensure that it is noticed.
+ */
+ if (al == NULL)
+ return -ECANCELED;
+
+ rgd = al->al_rgd;
+
if (rgrp_contains_block(rgd, ip->i_goal))
goal = ip->i_goal - rgd->rd_data0;
else
--
1.7.1.1