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

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Date:   Mon, 17 Feb 2020 16:40:26 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
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: crashdump: Re: [PATCH 2/2] printk: use the lockless ringbuffer

On Fri 2020-02-14 14:50:02, John Ogness wrote:
> Hi Lianbo,
> 
> On 2020-02-14, lijiang <lijiang@...hat.com> wrote:
> >> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> >> index 1ef6f75d92f1..d0d24ee1d1f4 100644
> >> --- a/kernel/printk/printk.c
> >> +++ b/kernel/printk/printk.c
> >> @@ -1062,21 +928,16 @@ void log_buf_vmcoreinfo_setup(void)
> >>  {
> >>  	VMCOREINFO_SYMBOL(log_buf);
> >>  	VMCOREINFO_SYMBOL(log_buf_len);
> >
> > I notice that the "prb"(printk tb static) symbol is not exported into
> > vmcoreinfo as follows:
> >
> > +	VMCOREINFO_SYMBOL(prb);
> >
> > 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 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).


Best Regards,
Petr