linux-kernel - Re: [4.9-rc3] BUG: unable to handle kernel paging request at ffffc900144dfc60

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Date:   Wed, 2 Nov 2016 08:54:43 -0600
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Borislav Petkov <bp@...en8.de>, Jann Horn <jann@...jh.net>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Tycho Andersen <tycho.andersen@...onical.com>
Subject: Re: [4.9-rc3] BUG: unable to handle kernel paging request at ffffc900144dfc60

On Wed, Nov 2, 2016 at 4:50 AM, Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>>
>> So I _think_ the fix is to just remove this. Perhaps something like
>> the attached? Adding scheduler people since this is in their code..
>
> That is not sufficient, for another Oops occurs inside stack_not_used().
> Since I don't want to break stack_not_used(), can we tolerate nested
> try_get_task_stack() usage and protect the whole sched_show_task()?

Sure, looks good to me.

But as Andy says, we should probably apply my patch too, just to get
rid of the useless hex printk and the ugly ifdeffery.

PeterZ/Ingo?

                Linus