From:   Alexey Makhalov <amakhalov@vmware.com>
To:     Michal Hocko <mhocko@suse.com>
CC:     Dennis Zhou <dennis@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "cl@linux.com" <cl@linux.com>,
        "mm-commits@vger.kernel.org" <mm-commits@vger.kernel.org>,
        "osalvador@suse.de" <osalvador@suse.de>,
        "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "tj@kernel.org" <tj@kernel.org>
Subject: Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree
Thread-Topic: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree
Thread-Index: AQHX1OJIWPaykZv/p0er2gRbWiPNoav64CoAgAABpgCAACaDAIAFMc8AgAQ2uwCAAAZtAIAAH/AAgACrTgA=
Date:   Mon, 15 Nov 2021 23:11:44 +0000
Message-ID: <ABEDED57-93A9-4601-8EB6-2FF348A0E0BB@vmware.com>
References: <20211108205031.UxDPHBZWa%akpm@linux-foundation.org>
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> On Nov 15, 2021, at 4:58 AM, Michal Hocko <mhocko@suse.com> wrote:
>=20
> On Mon 15-11-21 11:04:16, Alexey Makhalov wrote:
>> Hi Michal,
>>=20
>>>=20
>>> I have asked several times for details about the specific setup that =
has
>>> led to the reported crash. Without much success so far. Reproduction
>>> steps would be the first step. That would allow somebody to work on =
this
>>> at least if Alexey doesn't have time to dive into this deeper.
>>>=20
>>=20
>> I didn=E2=80=99t know that repro steps are still not clear.
>>=20
>> To reproduce the panic you need to have a system, where you can hot =
add
>> the CPU that belongs to memoryless NUMA node which is not present and =
onlined
>> yet. In other words, by hot adding CPU, you will add both CPU and =
NUMA node
>> at the same time.
>=20
> There seems to be something different in your setup because memory =
less
> nodes have reportedly worked on x86. I suspect something must be
> different in your setup. Maybe it is that you are adding a cpu that is
> outside of possible cpus intialized during boot time. Those should =
have
> their nodes initialized properly - at least per init_cpu_to_node. Your
> report doesn't really explain how the cpu is hotadded. Maybe you are
> trying to do something that has never been supported on x86.
Memoryless nodes are supported by x86. But hot add of such nodes not =
quite
done.

>=20
> It would be really great if you can provide more information in the
> original email thread. E.g. boot time messges and then more details
> about the hotplug operation as well (e.g. which cpu, the node
> association, how it is injected to the guest etc.).
>=20
I=E2=80=99ll provide more information in the main thread.


Regards,
=E2=80=94Alexey

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