[REVIEW] Check for valid agf_btreeblks with lazy counters enabled

["Barry Naujok" <bnaujok@xxxxxxx>]

Originally part of the libxfs/kernel sync up, the change to
xfs_alloc_read_agf() to check the agf_btreeblks value is less than
or equal to agf_length was unconditionally performed.

But, the actual implementation of maintaining agf_btreeblks
increments and decrements this regardless of whether lazy
counters are enabled or not. So, using a pre 2.6.23 filesystem
or a repaired one, this value could be anything.

So, in xfs_alloc_read_agf(), only validate agf_btreeblks if
lazy counters are in use.


--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -2272,6 +2272,9 @@ xfs_alloc_read_agf(
                be32_to_cpu(agf->agf_flfirst) < XFS_AGFL_SIZE(mp) &&
                be32_to_cpu(agf->agf_fllast) < XFS_AGFL_SIZE(mp) &&
                be32_to_cpu(agf->agf_flcount) <= XFS_AGFL_SIZE(mp);
+       if (xfs_sb_version_haslazysbcount(&mp->m_sb))
+               agf_ok = agf_ok && be32_to_cpu(agf->agf_btreeblks) <=
+                                                
be32_to_cpu(agf->agf_length);
        if (unlikely(XFS_TEST_ERROR(!agf_ok, mp, XFS_ERRTAG_ALLOC_READ_AGF,
                        XFS_RANDOM_ALLOC_READ_AGF))) {
                XFS_CORRUPTION_ERROR("xfs_alloc_read_agf",
@@ -2297,6 +2300,7 @@ xfs_alloc_read_agf(
 #ifdef DEBUG
        else if (!XFS_FORCED_SHUTDOWN(mp)) {
                ASSERT(pag->pagf_freeblks ==  
be32_to_cpu(agf->agf_freeblks));
+               ASSERT(pag->pagf_btreeblks ==  
be32_to_cpu(agf->agf_btreeblks));
                ASSERT(pag->pagf_flcount == be32_to_cpu(agf->agf_flcount));
                ASSERT(pag->pagf_longest == be32_to_cpu(agf->agf_longest));
                ASSERT(pag->pagf_levels[XFS_BTNUM_BNOi] ==