Use of copy_from_user in msm_gem_submit.c while holding a spin_lock

[Al Viro]

On Wed, Aug 17, 2016 at 03:24:38PM -0400, Rob Clark wrote:

> hmm, looks like, at least on arm (not sure about arm64),
> 
> #define __copy_from_user_inatomic __copy_from_user
> 
> ie. copy_from_user() minus the access_ok() and memset in the
> !access_ok() path.. but maybe what I want is just the
> pagefault_disable() if that disables copy_from_user() being able to
> block..

On a bunch of platforms copy_from_user() starts with might_sleep(); again,
that'll spread to all of the pretty soon.

Right now those primitives are very badly out of sync; this will change,
but let's not add more PITA sources.