On Tue, 27 Jun 2017 19:37:34 +0300, "Kirill A. Shutemov" said:

> > > commit c3aab7b2d4e8434d53bc81770442c14ccf0794a8
> > > Merge: 849c34f 93a7379
> > > Author: Stephen Rothwell
> > > Date:   Fri Jun 23 16:40:07 2017 +1000
> > >
> > >     Merge branch 'akpm-current/current'
> >
> > Hm is it really the merge of mmotm itself and not one of the patches in
> > mmotm?
> > Anyway smells like THP, adding Kirill.
>
> Okay, it took a while to figure it out.
>
> The bug is in patch "mm, gup: ensure real head page is ref-counted when
> using hugepages". We should look for a head *before* the loop. Otherwise
> 'page' may point to the first page beyond the compound page.
>
> The patch below should help.

Confirmed that fixes the BUGs that I was hitting.

Tested-By: Valdis Kletnieks <valdis.kletnieks@vt.edu>