[XFS] Fix use-after-free with log and quotas

Destroying the quota stuff on unmount can access the log - ie
XFS_QM_DONE() ends up in xfs_dqunlock() which calls
xfs_trans_unlocked_item() and then xfs_log_move_tail(). By this time the
log has already been destroyed. Just move the cleanup of the quota code
earlier in xfs_unmountfs() before the call to xfs_log_unmount(). Moving
XFS_QM_DONE() up near XFS_QM_DQPURGEALL() seems like a good spot.

SGI-PV: 987086

SGI-Modid: xfs-linux-melb:xfs-kern:32148a
Signed-off-by: NLachlan McIlroy <lachlan@sgi.com>
Signed-off-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NPeter Leckie <pleckie@sgi.com>

fs/xfs/xfs_mount.c

@@ -1245,6 +1245,9 @@ xfs_unmountfs(
 
 	XFS_QM_DQPURGEALL(mp, XFS_QMOPT_QUOTALL | XFS_QMOPT_UMOUNTING);
 
+	if (mp->m_quotainfo)
+		XFS_QM_DONE(mp);
+
 	/*
 	 * Flush out the log synchronously so that we know for sure
 	 * that nothing is pinned.  This is important because bflush()
@@ -1297,8 +1300,6 @@ xfs_unmountfs(
 	xfs_errortag_clearall(mp, 0);
 #endif
 	xfs_free_perag(mp);
-	if (mp->m_quotainfo)
-		XFS_QM_DONE(mp);
 }
 
 STATIC void