GFS2: Protect freeing directory hash table with i_lock spin_lock

This patch changes function gfs2_dir_hash_inval so it uses the
i_lock spin_lock to protect the in-core hash table, i_hash_cache.
This will prevent double-frees due to a race between gfs2_evict_inode
and inode invalidation.
Signed-off-by: Bob Peterson <rpeterso@redhat.com>

fs/gfs2/dir.c

@@ -388,8 +388,13 @@ static __be64 *gfs2_dir_get_hash_table(struct gfs2_inode *ip)
  */
 void gfs2_dir_hash_inval(struct gfs2_inode *ip)
 {
-	__be64 *hc = ip->i_hash_cache;
+	__be64 *hc;
+
+	spin_lock(&ip->i_inode.i_lock);
+	hc = ip->i_hash_cache;
 	ip->i_hash_cache = NULL;
+	spin_unlock(&ip->i_inode.i_lock);
+
 	kvfree(hc);
 }