linux-kernel - Re: [PATCH v4 0/3] arm64: support page mapping percpu first chunk allocator

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Date:   Sun, 10 Oct 2021 14:36:22 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     <will@...nel.org>, <catalin.marinas@....com>,
        <ryabinin.a.a@...il.com>, <andreyknvl@...il.com>,
        <dvyukov@...gle.com>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <elver@...gle.com>, <gregkh@...uxfoundation.org>,
        <kasan-dev@...glegroups.com>
Subject: Re: [PATCH v4 0/3] arm64: support page mapping percpu first chunk
 allocator

On Fri, 10 Sep 2021 13:33:51 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:

> Percpu embedded first chunk allocator is the firstly option, but it
> could fails on ARM64, eg,
>   "percpu: max_distance=0x5fcfdc640000 too large for vmalloc space 0x781fefff0000"
>   "percpu: max_distance=0x600000540000 too large for vmalloc space 0x7dffb7ff0000"
>   "percpu: max_distance=0x5fff9adb0000 too large for vmalloc space 0x5dffb7ff0000"
> 
> then we could meet "WARNING: CPU: 15 PID: 461 at vmalloc.c:3087 pcpu_get_vm_areas+0x488/0x838",
> even the system could not boot successfully.
> 
> Let's implement page mapping percpu first chunk allocator as a fallback
> to the embedding allocator to increase the robustness of the system.
> 
> Also fix a crash when both NEED_PER_CPU_PAGE_FIRST_CHUNK and KASAN_VMALLOC enabled.

How serious are these problems in real-world situations?  Do people
feel that a -stable backport is needed, or is a 5.16-rc1 merge
sufficient?