linux-kernel - Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk

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Date:   Thu, 24 May 2018 10:01:03 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Jia He <hejianet@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jia.he@...-semitech.com,
        Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in
 rmap_walk_ksm

On 24/05/18 09:50, Jia He wrote:
> Hi Suzuki
> 
> On 5/24/2018 4:44 PM, Suzuki K Poulose Wrote:
>> On 14/05/18 10:45, Suzuki K Poulose wrote:
>>> On 10/05/18 00:31, Andrew Morton wrote:
>>>> On Fri,  4 May 2018 11:11:46 +0800 Jia He <hejianet@...il.com> wrote:
>>>>
>>>>> In our armv8a server(QDF2400), I noticed lots of WARN_ON caused by PAGE_SIZE
>>>>> unaligned for rmap_item->address under memory pressure tests(start 20 guests
>>>>> and run memhog in the host).
>>>>>
>>>>> ...
>>>>>
>>>>> In rmap_walk_ksm, the rmap_item->address might still have the STABLE_FLAG,
>>>>> then the start and end in handle_hva_to_gpa might not be PAGE_SIZE aligned.
>>>>> Thus it will cause exceptions in handle_hva_to_gpa on arm64.
>>>>>
>>>>> This patch fixes it by ignoring(not removing) the low bits of address when
>>>>> doing rmap_walk_ksm.
>>>>>
>>>>> Signed-off-by: jia.he@...-semitech.com
>>>>
>>>> I assumed you wanted this patch to be committed as
>>>> From:jia.he@...-semitech.com rather than From:hejianet@...il.com, so I
>>>> made that change.  Please let me know if this was inappropriate.
>>>>
>>>> You can do this yourself by adding an explicit From: line to the very
>>>> start of the patch's email text.
>>>>
>>>> Also, a storm of WARN_ONs is pretty poor behaviour.  Is that the only
>>>> misbehaviour which this bug causes?  Do you think the fix should be
>>>> backported into earlier kernels?
>>>>
>>
>>
>> Jia, Andrew,
>>
>> What is the status of this patch ?
>>
>> Suzuki
> I thought the patch is merged into mmotm tree.
> http://www.ozlabs.org/~akpm/mmotm/series
> But I don't know what is the next step.

Hi Jia,

Thanks for the update. I think that should eventually hit mainline. When it does,
please could you send the patch to stable kernel versions too ?

Usually having a "Cc: stable@...nel.vger.org" in the original patch (for
critical fixes) would have done the trick. But since we don't have it,
please send it following the stable kernel rules.

Cheers
Suzuki