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

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Message-ID: <86BDA7AC-3E7A-4779-9388-9DF7BA7230AA@vmware.com>
Date:   Mon, 8 Nov 2021 06:12:11 +0000
From:   Alexey Makhalov <amakhalov@...are.com>
To:     David Hildenbrand <david@...hat.com>
CC:     Michal Hocko <mhocko@...e.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Oscar Salvador <OSalvador@...e.com>
Subject: Re: [PATCH] mm: fix panic in __alloc_pages

I’m going to send patch v2, with node_online check moved to caller (pcpu_alloc_pages() function)
as was suggested by David. It seems as it is only one place which passes present but offlined
node to alloc-pages_node(). Moving node online check to the caller keeps hot path (alloc_pages)
simple and performant.

> diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c
> index 2054c9213c43..c21ff5bb91dc 100644
> --- a/mm/percpu-vm.c
> +++ b/mm/percpu-vm.c
> @@ -84,15 +84,19 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk,
>                           gfp_t gfp)
> {
>       unsigned int cpu, tcpu;
> -       int i;
> +       int i, nid;
> 
>       gfp |= __GFP_HIGHMEM;
> 
>       for_each_possible_cpu(cpu) {
> +               nid = cpu_to_node(cpu);
> +
> +               if (nid == NUMA_NO_NODE || !node_online(nid))
> +                       nid = numa_mem_id();
>               for (i = page_start; i < page_end; i++) {
>                       struct page **pagep = &pages[pcpu_page_idx(cpu, i)];
> 
> -                       *pagep = alloc_pages_node(cpu_to_node(cpu), gfp, 0);
> +                       *pagep = alloc_pages_node(nid, gfp, 0);
>                       if (!*pagep)
>                               goto err;
>               }
> 

Thanks,
—Alexey


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