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

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>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 1280eff8af56..64a9e3cb9453 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,