Btrfs: avoid double free of fs_info->qgroup_ulist
Btrfs: avoid double free of fs_info->qgroup_ulist

When btrfs_read_qgroup_config or btrfs_quota_enable return non-zero, we've
already freed the fs_info->qgroup_ulist. The final btrfs_free_qgroup_config
called from quota_disable makes another ulist_free(fs_info->qgroup_ulist)
call.

We set fs_info->qgroup_ulist to NULL on the mentioned error paths, turning
the ulist_free in btrfs_free_qgroup_config into a noop.

Cc: Wang Shilong <2619f00d4b1c70e3aae124ec60dac0e454c5a3a3@cn.fujitsu.com>
Signed-off-by: Jan Schmidt <4f71970d0506cd4341522b2fa877abc3c9925755@jan-o-sch.net>
Signed-off-by: Josef Bacik <631dfb3d07694fdcf26abc7aac2c6c2b641f8bde@fusionio.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs