linux-kernel - Re: [PATCH] panic.c: export panic_on

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Message-ID: <20091012182346.GH17138@elte.hu>
Date:	Mon, 12 Oct 2009 20:23:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Simon Kagstrom <simon.kagstrom@...insight.net>,
	Artem Bityutskiy <dedekind1@...il.com>,
	David Woodhouse <dwmw2@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"Koskinen Aaro (Nokia-D/Helsinki)" <aaro.koskinen@...ia.com>,
	linux-mtd <linux-mtd@...ts.infradead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH] panic.c: export panic_on_oops


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Mon, 12 Oct 2009 08:36:38 -0700 (PDT) Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
> > I agree with the "save kernel buffer on panic" thing, but I disagree with 
> > making it anything new, and hooking into "printk()" or the console 
> > subsystem AT ALL. That's just bogus, stupid, and WRONG.
> > 
> > What you can do is to just flush the 'log_buf' buffer (or as much of it as 
> > you want - the buffer may be a megabyte in size, and maybe you only want 
> > to flush the last 8kB or something like that) on oops. And _not_ mix this 
> > up with anything else.
> 
> What he said.  I did it that way in the Digeo kernel back in 2002. 
> Worked good.
> 
> Doing it via a console is rather weird.  It will need core kernel 
> changes to do it properly.
> 
> Perhaps oops_enter() is a good place to mark the start of the log, and 
> flush it within oops_exit().

Simplest would be to do the last 2K in oops_exit()? That gives the oops, 
and the history leading up to it. Since the blocking is 2K, the extra 
log output is for free.

(unless the oops is larger than 2K - but that is rather rare.)

	Ingo
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