linux-kernel - Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section

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Message-ID: <87pohaxam1.fsf@xmission.com>
Date:   Tue, 21 Mar 2017 22:18:30 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Dave Young <dyoung@...hat.com>
Cc:     Xunlei Pang <xlpang@...hat.com>, Baoquan He <bhe@...hat.com>,
        Petr Tesarik <ptesarik@...e.cz>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        Atsushi Kumagai <ats-kumagai@...jp.nec.com>
Subject: Re: [PATCH v3 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section

Dave Young <dyoung@...hat.com> writes:

> On 03/20/17 at 10:33pm, Eric W. Biederman wrote:
>> Xunlei Pang <xlpang@...hat.com> writes:
>> 
>> > As Eric said,
>> > "what we need to do is move the variable vmcoreinfo_note out
>> > of the kernel's .bss section.  And modify the code to regenerate
>> > and keep this information in something like the control page.
>> >
>> > Definitely something like this needs a page all to itself, and ideally
>> > far away from any other kernel data structures.  I clearly was not
>> > watching closely the data someone decided to keep this silly thing
>> > in the kernel's .bss section."
>> >
>> > This patch allocates extra pages for these vmcoreinfo_XXX variables,
>> > one advantage is that it enhances some safety of vmcoreinfo, because
>> > vmcoreinfo now is kept far away from other kernel data structures.
>> 
>> Can you preceed this patch with a patch that removes CRASHTIME from
>> vmcoreinfo?  If someone actually cares we can add a separate note that holds
>> a 64bit crashtime in the per cpu notes.  
>
> I think makedumpfile is using it, but I also vote to remove the
> CRASHTIME. It is better not to do this while crashing and a makedumpfile
> userspace patch is needed to drop the use of it.
>
>> 
>> As we are looking at reliability concerns removing CRASHTIME should make
>> everything in vmcoreinfo a boot time constant.  Which should simplify
>> everything considerably.
>
> It is a nice improvement..

We also need to take a close look at what s390 is doing with vmcoreinfo.
As apparently it is reading it in a different kind of crashdump process.

Eric