linux-kernel - Re: [PATCH v3] mm: fix panic in __alloc

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Date:   Tue, 16 Nov 2021 10:17:07 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Alexey Makhalov <amakhalov@...are.com>
Cc:     Dennis Zhou <dennis@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v3] mm: fix panic in __alloc_pages

On Tue 16-11-21 01:31:44, Alexey Makhalov wrote:
[...]
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 6737b1cbf..bbc1a70d5 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -200,6 +200,10 @@ static int acpi_processor_hotadd_init(struct acpi_processor *pr)
>          * gets online for the first time.
>          */
>         pr_info("CPU%d has been hot-added\n", pr->id);
> +       {
> +               int nid = cpu_to_node(pr->id);
> +               printk("%s:%d cpu %d, node %d, online %d, ndata %p\n", __FUNCTION__, __LINE__, pr->id, nid, node_online(nid), NODE_DATA(nid));
> +       }
>         pr->flags.need_hotplug_init = 1;

OK, IIUC you are adding a processor which is outside of
possible_cpu_mask and that means that the node is not allocated for such
a future to be hotplugged cpu and its memory node. init_cpu_to_node
would have done that initialization otherwise. I think you want to talk
to x86 maintainers and people who have introduced a support for
memoryless nodes for x86.

To me it seems like you are trying to use a functionality that has
never been properly implemented. I do not remember how other acpi based
architectures handle this and maybe we need a generic solution and that
would bring up the node as soon as a new cpu is hot added.
-- 
Michal Hocko
SUSE Labs