[BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

[Sebastian Ott]

On Wed, 24 Feb 2016, Martin Schwidefsky wrote:
> On Tue, 23 Feb 2016 22:33:45 +0300
> "Kirill A. Shutemov" <kirill at shutemov.name> wrote:
> 
> > On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:
> > > I'll check with Martin, maybe it is actually trivial, then we can
> > > do a quick test it to rule that one out.
> > 
> > Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
> > _the_ bug.
> > 
> > pmdp_invalidate() is called for the wrong address :-/
> > I guess that can be destructive on the architecture, right?
> > 
> > Could you check this?
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index 1c317b85ea7d..4246bc70e55a 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -2865,7 +2865,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> >  	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
> >  	pmd_populate(mm, &_pmd, pgtable);
> > 
> > -	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> > +	for (i = 0; i < HPAGE_PMD_NR; i++) {
> >  		pte_t entry, *pte;
> >  		/*
> >  		 * Note that NUMA hinting access restrictions are not
> > @@ -2886,9 +2886,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> >  		}
> >  		if (dirty)
> >  			SetPageDirty(page + i);
> > -		pte = pte_offset_map(&_pmd, haddr);
> > +		pte = pte_offset_map(&_pmd, haddr + i * PAGE_SIZE);
> >  		BUG_ON(!pte_none(*pte));
> > -		set_pte_at(mm, haddr, pte, entry);
> > +		set_pte_at(mm, haddr + i * PAGE_SIZE, pte, entry);
> >  		atomic_inc(&page[i]._mapcount);
> >  		pte_unmap(pte);
> >  	}
> > @@ -2938,7 +2938,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> >  	pmd_populate(mm, pmd, pgtable);
> > 
> >  	if (freeze) {
> > -		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
> > +		for (i = 0; i < HPAGE_PMD_NR; i++) {
> >  			page_remove_rmap(page + i, false);
> >  			put_page(page + i);
> >  		}
> 
> Test is running and it looks good so far. For the final assessment I defer
> to Gerald and Sebastian.
> 

Yes, that one worked. My testsystem is doing make -j10 && make clean
in a loop since 4 hours now. Thanks!

Sebastian