From: Michal Hocko <mhocko@kernel.org>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
zhongjiang <zhongjiang@huawei.com>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: fix account pmd page to the process
Date: Fri, 17 Jun 2016 15:00:00 +0200 [thread overview]
Message-ID: <20160617125959.GH21670@dhcp22.suse.cz> (raw)
In-Reply-To: <20160617122506.GC6534@node.shutemov.name>
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@linux.intel.com>
> 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@linux.intel.com>
> Reported-by: zhongjiang <zhongjiang@huawei.com>
> Fixes: dc6c9a35b66b ("mm: account pmd page tables to the process")
> Cc: <stable@vger.kernel.org> [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 <mhocko@suse.com>
> ---
> 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
next prev parent reply other threads:[~2016-06-17 13:00 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-16 11:36 [PATCH] mm: fix account pmd page to the process zhongjiang
2016-06-16 15:42 ` Michal Hocko
2016-06-16 15:43 ` Michal Hocko
2016-06-16 16:05 ` Mike Kravetz
2016-06-16 16:31 ` Michal Hocko
2016-06-16 16:47 ` Mike Kravetz
2016-06-17 12:25 ` Kirill A. Shutemov
2016-06-17 13:00 ` Michal Hocko [this message]
2016-06-17 14:25 ` Kirill A. Shutemov
2016-06-17 15:39 ` Mike Kravetz
2016-06-18 5:07 ` zhong jiang
2016-06-17 11:18 ` zhong jiang
[not found] <1466163941-12952-1-git-send-email-zhongjiang@huawei.com>
2016-06-17 12:01 ` zhong jiang
-- strict thread matches above, loose matches on Subject: below --
2016-06-17 11:56 zhongjiang
2016-06-17 12:21 ` Michal Hocko
2016-06-17 13:04 ` zhong jiang
[not found] <1466076175-23444-1-git-send-email-zhongjiang@huawei.com>
2016-06-16 11:30 ` zhong jiang
2016-06-16 11:28 zhongjiang
2016-06-16 11:17 zhongjiang
2016-06-16 11:16 zhongjiang
2016-06-16 11:13 zhongjiang
2016-06-16 7:47 zhongjiang
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