Yes, I don't need to EXPORT this symbol again.
i have modified this patch and re-committed it.  The email link is :
https://lkml.org/lkml/2018/12/18/8
this patch you see is old.

thanks and regards

Matthew Wilcox <willy@infradead.org> 于2018年12月18日周二 下午8:47写道：

> On Tue, Dec 18, 2018 at 11:42:11AM +0800, gchen.guomin@gmail.com wrote:
> > +EXPORT_SYMBOL(mm_update_next_owner);
>
> Unless you've figured out how to build mmu_context.c as a module, you
> don't need to EXPORT the symbol.  Just the below hunk is enough.
>
> > diff --git a/mm/mmu_context.c b/mm/mmu_context.c
> > index 3e612ae..9eb81aa 100644
> > --- a/mm/mmu_context.c
> > +++ b/mm/mmu_context.c
> > @@ -60,5 +60,6 @@ void unuse_mm(struct mm_struct *mm)
> >       /* active_mm is still 'mm' */
> >       enter_lazy_tlb(mm, tsk);
> >       task_unlock(tsk);
> > +     mm_update_next_owner(mm);
> >  }
> >  EXPORT_SYMBOL_GPL(unuse_mm);
> > --
> > 1.8.3.1
> >
>