If your plain dm-crypt partition failed to decrypt after upgrade, with the following error message:

WARNING: using default options for hash (sha256) that could be incompatible with old versions.

This is the solution.

Root Cause

After upgrading cryptsetup from 2.6.1 to 2.7.0, the default hash algorithm for plain mode changed from ripemd160 to sha256. Ref: https://mirrors.edge.kernel.org/pub/linux/utils/cryptsetup/v2.7/v2.7.0-rc0-ReleaseNotes

Solution

If you are using cryptsetup command line, please add --hash ripemd160. If you are mounting with kernel parameter, please use crypto=ripemd160:<YourAlgorithm>:<YourKeySize>:<YourOffset>:.