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

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Date:	Mon, 12 Oct 2009 21:14:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...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


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Mon, 12 Oct 2009, Ingo Molnar wrote:
> > 
> > * Andrew Morton <akpm@...ux-foundation.org> wrote:
> > > 
> > > 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.
> 
> I agree, except I don't think it should be fixed to 2k.

Yeah - i cited 2K only because that is what mtdoops uses.

>       	void dump_kmsg(void)
> [...]
>
> Look ma, no locking, no buffer allocations, no nothing.

Neat ...

This could also be used for a warm-reboot preserve-memory thing as well. 
A well-known 4K (or so) area to preserve and print out during the next 
bootup after a crash. dump_kmsg() could copy the kernel's last will out 
to that area, or so.

That would be cross-kernel compatible and the newly booted kernel image 
wouldnt overwrite this area. (which it does currently via its 
__log_buf[])

	Ingo
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