On Mon, Feb 9, 2015 at 5:42 PM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
> On Sat, Feb 07, 2015 at 08:33:02AM +0100, Sedat Dilek wrote:
>> On Sat, Feb 7, 2015 at 6:12 AM, Pat Erley <pat-lkml@xxxxxxxxx> wrote:
>> > I'm seeing the message in $subject on my Xen DOM0 on next-20150204 on
>> > x86_64. I haven't had time to bisect it, but have seen some discussion on
>> > similar topics here recently. I can trigger this pretty reliably by
>> > watching Netflix. At some point (minutes to hours) into it, the netflix
>> > video goes black (audio keeps going, so it still thinks it's working) and
>> > the error appears in dmesg. Refreshing the page gets the video going again,
>> > and it will continue playing for some indeterminate amount of time.
>> >
>> > Kirill, I've CC'd you as looking in the logs, you've patched a false
>> > positive trigger of this very recently(patch in kernel I'm running). Am I
>> > actually hitting a problem, or is this another false positive case? Any
>> > additional details that might help?
>> >
>> > Dmesg from system attached.
>>
>> [ CC some mm folks ]
>>
>> I have seen this, too.
>>
>> root# grep "BUG: non-zero nr_pmds on freeing mm:" /var/log/kern.log | wc -l
>> 21
>>
>> Checking my logs: On next-20150203 and next-20150204.
>>
>> I am here not in a VM environment and cannot say what causes these messages.
>
> Sorry, my fault.
>
> The patch below should fix that.
>
> From 11bce596e653302e41f819435912f01ca8cbc27e Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Date: Mon, 9 Feb 2015 18:34:56 +0200
> Subject: [PATCH] mm: fix race on pmd accounting
>
> Do not account the pmd table to the process if other thread allocated it
> under us.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Still building with the fix...
Please feel free to add Pat as a reporter.
Reported-by: Pat Erley <pat-lkml@xxxxxxxxx>
Is that fixing...?
commit daa1b0f29cdccae269123e7f8ae0348dbafdc3a7
"mm: account pmd page tables to the process"
If yes, please add a Fixes-tag [2]...
Fixes: daa1b0f29cdc ("mm: account pmd page tables to the process")
I will re-test with LTP/mmap and report.
- Sedat -
[1] http://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/commit/?id=daa1b0f29cdccae269123e7f8ae0348dbafdc3a7
[2] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/SubmittingPatches#n164
> ---
> mm/memory.c | 15 ++++++++-------
> 1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index 8ae52c918415..802adda2b0b6 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3350,17 +3350,18 @@ int __pmd_alloc(struct mm_struct *mm, pud_t *pud, unsigned long address)
> smp_wmb(); /* See comment in __pte_alloc */
>
> spin_lock(&mm->page_table_lock);
> - mm_inc_nr_pmds(mm);
> #ifndef __ARCH_HAS_4LEVEL_HACK
> - if (pud_present(*pud)) /* Another has populated it */
> - pmd_free(mm, new);
> - else
> + if (!pud_present(*pud)) {
> + mm_inc_nr_pmds(mm);
> pud_populate(mm, pud, new);
> -#else
> - if (pgd_present(*pud)) /* Another has populated it */
> + } else /* Another has populated it */
> pmd_free(mm, new);
> - else
> +#else
> + if (!pgd_present(*pud)) {
> + mm_inc_nr_pmds(mm);
> pgd_populate(mm, pud, new);
> + } else /* Another has populated it */
> + pmd_free(mm, new);
> #endif /* __ARCH_HAS_4LEVEL_HACK */
> spin_unlock(&mm->page_table_lock);
> return 0;
> --
> Kirill A. Shutemov
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