Windows Server 2012 R2 Hyper-V hosts may crash in the csvfs.sys file process when you perform backup with certain backup applications.
This issue occurs if a backup solution sends the CsvControlQueryFileRevision request on a cleaned-up file object. In that situation, CSVFS may crash because one of its internal functions assumes that a valid file object will be passed.
How to get this update
Method 1: Windows Update
This update is available through Windows Update. For more information about how to run Windows Update, see How to get an update through Windows Update.
Method 2: Microsoft Update Catalog
To get the stand-alone package for this update, go to the Microsoft Update Catalog website.
To install this update, you must have the April 2014 update rollup for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 (2919355) installed in Windows Server 2012 R2.
To apply this update, you don't have to make any changes to the registry.
You may have to restart the computer after you apply this update.
Update replacement information
This update doesn't replace a previously released update.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.