linux-kernel - Re: crashdump: Re: [PATCH 2/2] printk: use the lockless ringbuffer

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Message-ID: <87zhdh9oo1.fsf@linutronix.de>
Date:   Mon, 17 Feb 2020 17:14:22 +0100
From:   John Ogness <john.ogness@...utronix.de>
To:     Petr Mladek <pmladek@...e.com>
Cc:     lijiang <lijiang@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrea Parri <parri.andrea@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: crashdump: Re: [PATCH 2/2] printk: use the lockless ringbuffer

On 2020-02-17, Petr Mladek <pmladek@...e.com> wrote:
>>> Should the "prb"(printk tb static) symbol be exported into
>>> vmcoreinfo?  Otherwise, do you happen to know how to walk through
>>> the log_buf and get all kernel logs from vmcore?
>> 
>> You are correct. This will need to be exported as well so that the
>> descriptors can be accessed. (log_buf is only the pure human-readable
>> text.) I am currently hacking the crash tool to see exactly what
>> needs to be made available in order to access all the data of the
>> ringbuffer.
>
> I am not sure which parts you are working on. Are you going to provide
> also patch for makedumpfile, please?

I'm working on crash first. makedumpfile is on my list as well.

> I get the following failure when creating the crashdump using:
>
>     echo c >/proc/sysrq-trigger
>
>
> The kernel version is not supported.
> The makedumpfile operation may be incomplete.
> dump_dmesg: Can't find variable-length record symbols
> makedumpfile Failed.
> Running makedumpfile --dump-dmesg /proc/vmcore failed (1).

Yes, the symbols have changed (and some are missing). I will get this
sorted out for v2. And I will provide some heavily hacked code for crash
and makedumpfile to show that the necessary symbols are there and it
works.

John Ogness