From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933591AbcFQNAE (ORCPT ); Fri, 17 Jun 2016 09:00:04 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:34978 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933415AbcFQNAC (ORCPT ); Fri, 17 Jun 2016 09:00:02 -0400 Date: Fri, 17 Jun 2016 15:00:00 +0200 From: Michal Hocko To: "Kirill A. Shutemov" Cc: Mike Kravetz , zhongjiang , akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: fix account pmd page to the process Message-ID: <20160617125959.GH21670@dhcp22.suse.cz> References: <1466076971-24609-1-git-send-email-zhongjiang@huawei.com> <20160616154214.GA12284@dhcp22.suse.cz> <20160616154324.GN6836@dhcp22.suse.cz> <71df66ac-df29-9542-bfa9-7c94f374df5b@oracle.com> <20160616163119.GP6836@dhcp22.suse.cz> <20160617122506.GC6534@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160617122506.GC6534@node.shutemov.name> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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" > 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 > Reported-by: zhongjiang > Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process") > Cc: [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(). Acked-by: Michal Hocko > --- > mm/hugetlb.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index e197cd7080e6..ed6a537f0878 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -4216,7 +4216,6 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > if (saddr) { > spte = huge_pte_offset(svma->vm_mm, saddr); > if (spte) { > - mm_inc_nr_pmds(mm); > get_page(virt_to_page(spte)); > break; > } > @@ -4231,9 +4230,9 @@ pte_t *huge_pmd_share(struct mm_struct *mm, unsigned long addr, pud_t *pud) > if (pud_none(*pud)) { > pud_populate(mm, pud, > (pmd_t *)((unsigned long)spte & PAGE_MASK)); > + mm_inc_nr_pmds(mm); > } else { > put_page(virt_to_page(spte)); > - mm_inc_nr_pmds(mm); > } > spin_unlock(ptl); > out: > -- > Kirill A. Shutemov -- Michal Hocko SUSE Labs