quota: Fix double lock in add_dquot_ref() with CONFIG_QUOTA_DEBUG

When CONFIG_QUOTA_DEBUG is enabled we call inode_get_rsv_space() from
add_dquot_ref() while holding i_lock. But inode_get_rsv_space() is trying
to get i_lock as well resulting in double lock.

Fix the problem by moving inode_get_rsv_space() call out of i_lock.

Reported-and-analyzed-by: Jie Liu <jeff.liu@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

fs/quota/dquot.c

@@ -907,14 +907,14 @@ static void add_dquot_ref(struct super_block *sb, int type)
 			spin_unlock(&inode->i_lock);
 			continue;
 		}
-#ifdef CONFIG_QUOTA_DEBUG
-		if (unlikely(inode_get_rsv_space(inode) > 0))
-			reserved = 1;
-#endif
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
 		spin_unlock(&inode_sb_list_lock);
 
+#ifdef CONFIG_QUOTA_DEBUG
+		if (unlikely(inode_get_rsv_space(inode) > 0))
+			reserved = 1;
+#endif
 		iput(old_inode);
 		__dquot_initialize(inode, type);