linux-kernel - Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud mapping

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Message-ID: <YdgbwpECTXGCJZ/0@arm.com>
Date:   Fri, 7 Jan 2022 10:53:54 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Jianyong Wu <Jianyong.Wu@....com>
Cc:     "will@...nel.org" <will@...nel.org>,
        Anshuman Khandual <Anshuman.Khandual@....com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "david@...hat.com" <david@...hat.com>,
        "quic_qiancai@...cinc.com" <quic_qiancai@...cinc.com>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "gshan@...hat.com" <gshan@...hat.com>,
        Justin He <Justin.He@....com>, nd <nd@....com>
Subject: Re: [PATCH v3] arm64/mm: avoid fixmap race condition when create pud
 mapping

On Fri, Jan 07, 2022 at 09:10:57AM +0000, Jianyong Wu wrote:
> I roughly find the root cause.
>  alloc_init_pud will be called at the very beginning of kernel boot in
>  create_mapping_noalloc where no memory allocator is initialized. But
>  lockdep check may need allocate memory. So, kernel take exception
>  when acquire lock.(I have not found the exact code that cause this
>  issue) that's say we may not be able to use a lock so early.

I couldn't find an slab or page allocation place either. It would be
nice to get to the root cause rather than just avoiding the mutex on the
early boot path.

-- 
Catalin