6.10.4 is a bugfix release over 6.10.3. Very few changes have been made. They are listed below.
Fixed a segfault that could occur when calling mkWeakForeignEnv#.
Fixed a crash that could occur when calling unblock inside unsafePerformIO.
Stop primops such as readMutVar# being inlined, which can cause loss of referential transparency.
Fixed a bug that meant ctrl-C was ignored by processes we run with runProcess.
Fixed a bug where gcc processes run by GHC get killed on Mac OS X 10.4.11.
Fixed a bug where processes on Windows could hold file handles open after they had finished, leading to permission denied errors.
GHCi only uses Haskeline if the input is a terminal.
Fixed building with newer versions of MSYS binutils.