Re: [PATCH] mm: fix account pmd page to the process

[Kirill A. Shutemov]

On Fri, Jun 17, 2016 at 03:00:00PM +0200, Michal Hocko wrote:
> On Fri 17-06-16 15:25:06, Kirill A. Shutemov wrote:
> [...]
> > >From fd22922e7b4664e83653a84331f0a95b985bff0c Mon Sep 17 00:00:00 2001
> > From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Date: Fri, 17 Jun 2016 15:07:03 +0300
> > Subject: [PATCH] hugetlb: fix nr_pmds accounting with shared page tables
> > 
> > We account HugeTLB's shared page table to all processes who share it.
> > The accounting happens during huge_pmd_share().
> > 
> > If somebody populates pud entry under us, we should decrease pagetable's
> > refcount and decrease nr_pmds of the process.
> > 
> > By mistake, I increase nr_pmds again in this case. :-/
> > It will lead to "BUG: non-zero nr_pmds on freeing mm: 2" on process'
> > exit.
> > 
> > Let's fix this by increasing nr_pmds only when we're sure that the page
> > table will be used.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > Reported-by: zhongjiang <zhongjiang@xxxxxxxxxx>
> > Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process")
> > Cc: <stable@xxxxxxxxxxxxxxx>        [4.0+]
> 
> Yes this patch is better. Is it worth backporting to stable though?
> BUG message sounds scary but it is not a real BUG().

I guess, we can live without stable backport.
> 
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>

Thanks.

-- 
 Kirill A. Shutemov