linux-kernel - Re: [PATCH 1/3] ring-buffer: Add uname to match criteria for persistent ring buffer

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Message-ID: <CAHk-=wg5Kcr=sBuZcWs90CSGbJuKy0QsLaCC5oD15gS+Hk8j1A@mail.gmail.com>
Date: Tue, 17 Dec 2024 09:46:30 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	stable@...r.kernel.org
Subject: Re: [PATCH 1/3] ring-buffer: Add uname to match criteria for
 persistent ring buffer

On Tue, 17 Dec 2024 at 09:34, Steven Rostedt <rostedt@...dmis.org> wrote:
>
> Add uname into the meta data and if the uname in the meta data from the
> previous boot does not match the uname of the current boot, then clear the
> buffer and re-initialize it.

This seems broken.

The problem is not that the previous boot data is wrong.

The problem is that you printed it *out* wrong by trying to interpret
pointers in it.

Now you basically hide that, and make it harder to see any data from a
bad kernel (since you presumably need to boot into a good kernel to do
analysis).

The real fix seems to have been your 3/3, which still prints out the
data, but stops trying to interpret the pointers in it.

Except you should also remove the last_text_delta / last_data_delta
stuff. That's all about exactly that "trying to interpret bogus
pointers". Instead you seem to have actually just *added* a case of
that in your 3/3.

           Linus