remove set_fs calls from the exec and coredump code v2

[Christoph Hellwig]

On Fri, Apr 17, 2020 at 05:41:52PM -0500, Eric W. Biederman wrote:
> > this series gets rid of playing with the address limit in the exec and
> > coredump code.  Most of this was fairly trivial, the biggest changes are
> > those to the spufs coredump code.
> >
> > Changes since v1:
> >  - properly spell NUL
> >  - properly handle the compat siginfo case in ELF coredumps
> 
> Quick question is exec from a kernel thread within the scope of what you
> are looking at?
> 
> There is a set_fs(USER_DS) in flush_old_exec whose sole purpose appears
> to be to allow exec from kernel threads.  Where the kernel threads
> run with set_fs(KERNEL_DS) until they call exec.

This series doesn't really look at that area.  But I don't think exec
from a kernel thread makes any sense, and cleaning up how to set the
initial USER_DS vs KERNEL_DS state is something I'll eventually get to,
it seems like a major mess at the moment.