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Date:   Sun, 10 Oct 2021 14:36:22 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Kefeng Wang <wangkefeng.wang@huawei.com>
Cc:     <will@kernel.org>, <catalin.marinas@arm.com>,
        <ryabinin.a.a@gmail.com>, <andreyknvl@gmail.com>,
        <dvyukov@google.com>, <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
        <elver@google.com>, <gregkh@linuxfoundation.org>,
        <kasan-dev@googlegroups.com>
Subject: Re: [PATCH v4 0/3] arm64: support page mapping percpu first chunk
 allocator
Message-Id: <20211010143622.18f491df5591d039cda8f7b7@linux-foundation.org>
In-Reply-To: <20210910053354.26721-1-wangkefeng.wang@huawei.com>
References: <20210910053354.26721-1-wangkefeng.wang@huawei.com>
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On Fri, 10 Sep 2021 13:33:51 +0800 Kefeng Wang <wangkefeng.wang@huawei.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?