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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 9 Jul 2019 11:11:16 +0200
Message-ID: <CACRpkdbgMyYYm1v4BeFQBCz8jZVLE_0oZiKu5F3Rt6=ccfVnYA@mail.gmail.com>
Subject: Re: [PATCH] ARM: mm: only adjust sections of valid mm structures
To:     Doug Berger <opendmb@gmail.com>
Cc:     Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Russell King <linux@armlinux.org.uk>,
        Laura Abbott <labbott@redhat.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Rob Herring <robh@kernel.org>,
        "Steven Rostedt (VMware)" <rostedt@goodmis.org>,
        Peng Fan <peng.fan@nxp.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Thu, Jun 27, 2019 at 11:33 PM Doug Berger <opendmb@gmail.com> wrote:

> A timing hazard exists when an early fork/exec thread begins
> exiting and sets its mm pointer to NULL while a separate core
> tries to update the section information.
>
> This commit ensures that the mm pointer is not NULL before
> setting its section parameters. The arguments provided by
> commit 11ce4b33aedc ("ARM: 8672/1: mm: remove tasklist locking
> from update_sections_early()") are equally valid for not
> requiring grabbing the task_lock around this check.
>
> Fixes: 08925c2f124f ("ARM: 8464/1: Update all mm structures with section adjustments")
> Signed-off-by: Doug Berger <opendmb@gmail.com>

Cc: stable@vger.kernel.org ?

I'm not smart enough to say whether it is the right solution, but
I also want to test this on some boards I have. I suspect this
may be part of the problem I have with mounting root on a USB
stick on some early mpcore machines, so I might come back with
a Tested-by.

Yours,
Linus Walleij