linux-kernel - Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree

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Message-ID: <ABEDED57-93A9-4601-8EB6-2FF348A0E0BB@vmware.com>
Date:   Mon, 15 Nov 2021 23:11:44 +0000
From:   Alexey Makhalov <amakhalov@...are.com>
To:     Michal Hocko <mhocko@...e.com>
CC:     Dennis Zhou <dennis@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cl@...ux.com" <cl@...ux.com>,
        "mm-commits@...r.kernel.org" <mm-commits@...r.kernel.org>,
        "osalvador@...e.de" <osalvador@...e.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "tj@...nel.org" <tj@...nel.org>
Subject: Re: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree



> On Nov 15, 2021, at 4:58 AM, Michal Hocko <mhocko@...e.com> wrote:
> 
> On Mon 15-11-21 11:04:16, Alexey Makhalov wrote:
>> Hi Michal,
>> 
>>> 
>>> 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.
>>> 
>> 
>> I didn’t know that repro steps are still not clear.
>> 
>> 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.
> 
> 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.

> 
> 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.).
> 
I’ll provide more information in the main thread.



Regards,
—Alexey

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