After installing SharePoint 2013 CU 201601, the User Profile Sync service stopped working. After two days of struggling, it seems the best solution is to reinstall SharePoint.
That's fine. The whole lab farm only have two servers.
I uninstalled SharePoint 2013 components on those two servers, then deleted all databases and IIS web folders. Then start to reinstall SharePoint.
Everything is fine, until I tried to join the second server to the newly created farm. An error message popped up: "Failed to call GetTypes on assembly Microsoft.AnalysisServices.SPAddin"
This is strange, as I am pretty sure that PowerPivot was uninstalled. I am not the only one who ever got this problem. It seems the easiest way is to install PowerPivot add-on on all servers.
However, I prefer not to create a clean OOTB SharePoint farm.
It turns out quite easy to fix this problem: search for "Microsoft.AnalysisServices.SPAddin" on hard disk on all servers, and then delete all relevant folders and files. Then reboot the servers.
All the files and folders are in "C:\Windows\Microsoft.NET\assembly" or "C:\Program Files\Common Files\microsoft shared\Web Server Extensions".