Re: kernel BUG at mm/gup.c:LINE!

[Michal Hocko <mhocko@kernel.org>]

On Thu 05-07-18 14:30:17, Oscar Salvador wrote:
> On Thu, Jul 05, 2018 at 09:18:39AM +0200, Oscar Salvador wrote:
> >  
> > > This is more than unexpected. The patch merely move the alignment check
> > > up. I will try to investigate some more but I am off for next four days
> > > and won't be online most of the time.
> > > 
> > > Btw. does the same happen if you keep do_brk helper and add the length
> > > sanitization there as well?
> 
> I took another look.
> The problem was that while deleting the check in do_brk_flags(), this left then "len"
> local variable with an unset value, but we need it to contain the request value
> because we do use it in further calls in do_brk_flags(), like:

Very well spotted. Thanks for noticing! I am really half online so I
cannot give it much testing right now. But here is the updated patch
with the changelog. I cannot really tell whether the other change to
align up in load_elf_library is correct as well. It seems OK but
everything around elf loading is tricky from my past experience.

My patch simply makes vm_brk_flags behavior consistent so I believe we
should do that regardless (unless I've screwed something else here of
course).