linux-kernel - Re: a question about how to debug this case in ftrace

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Message-ID: <87h6dhxgel.fsf@jogness.linutronix.de>
Date: Tue, 25 Jun 2024 16:15:54 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Steven Rostedt <rostedt@...dmis.org>, Andrew Halaney <ahalaney@...hat.com>
Cc: Song Chen <chensong_2000@....cn>, Derek Barbosa <debarbos@...hat.com>,
 pmladek@...e.com, senozhatsky@...omium.org,
 linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 williams@...hat.com, jlelli@...hat.com
Subject: Re: a question about how to debug this case in ftrace

On 2024-06-25, Steven Rostedt <rostedt@...dmis.org> wrote:
> You may be interested in some work I'm doing that allows you to read
> the ring buffer from a previous kernel after a crash.
>
> https://lore.kernel.org/linux-trace-kernel/20240612231934.608252486@goodmis.org/
>
> I also have a way to ask for any memory, that should be able to get the
> same location most times, via a "reserve_mem=" kernel command line
> parameter.
>
> https://lore.kernel.org/linux-trace-kernel/20240613233415.734483785@goodmis.org/
>
> They are both destined for the next merge window. After that, I have
> one more patch that ties the two together, so that you can have a
> kernel command line of:
>
>  reserve_mem=12M:4096:trace trace_instance=bootmap@...ce
>
> and then when you boot up, you would have a trace instance that would
> be mapped to that memory. If your machine doesn't clear memory after a
> crash, you can read the data from the crash on the next boot.

Nice. Thanks for the heads up. It will be nice to implement a "printk"
label as well. ;-)

John Ogness