[PATCH] Btrfs: set qgroup_ulist to be null after calling ulist_free()

[Wang Shilong <wangshilong1991@gmail.com>]

From: Wang Shilong <wangsl.fnst@cn.fujitsu.com>

We call ulist_free(qgroup_ulist) in btrfs_free_qgroup_config(),
and btrfs_free_qgroup_config() may be called in two cases:

(1)umount filesystem
(2)disabling quota

However, if we firstly disable quota and then umount filesystem,
a double free happens. Fix it.

Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
---
 fs/btrfs/qgroup.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 1280eff..64a9e3c 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -460,7 +460,13 @@ void btrfs_free_qgroup_config(struct btrfs_fs_info *fs_info)
 		}
 		kfree(qgroup);
 	}
+	/*
+	 * we call btrfs_free_qgroup_config() when umounting
+	 * filesystem and disabling quota, so we set qgroup_ulit
+	 * to be null here to avoid double free.
+	 */
 	ulist_free(fs_info->qgroup_ulist);
+	fs_info->qgroup_ulist = NULL;
 }
 
 static int add_qgroup_relation_item(struct btrfs_trans_handle *trans,
-- 
1.7.11.7