linux-kernel - Re: Query about kdump_msg hook into crash

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Message-ID: <m1hbcous3o.fsf@fess.ebiederm.org>
Date:	Mon, 31 Jan 2011 23:33:15 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	Vivek Goyal <vgoyal@...hat.com>, kosaki.motohiro@...fujitsu.com,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Jarod Wilson <jwilson@...hat.com>
Subject: Re: Query about kdump_msg hook into crash_kexec()

Américo Wang <xiyou.wangcong@...il.com> writes:

> On Mon, Jan 31, 2011 at 05:59:39PM -0500, Vivek Goyal wrote:
>>
>>Anyway, if an image is loaded and we have setup to capture dump also
>>why do we need to save kmsg with the help of an helper. I am assuming
>>this is more of a debugging aid if we have no other way to capture the
>>kernel log buffer. So if somebody has setup kdump to capture the
>>vmcore, why to call another handler which tries to save part of the
>>vmcore (kmsg) separately.
>>
>
> Well, kmsg dumper is not only for panic/oops, it can also save kernel
> messages when the system is reboot/halt.
>
> Yeah, it is true that vmcore contains log_buf, but I think the users
> of ramoops/mtdoops are mainly those who don't have kdump configured
> in their kernels, they are cheaper than kdump, but less powerful

The issue is the inane call inside crash_kexec.

It requires both a kexec kernel to be loaded and it requires you to be
crashing.  Given that when I audited the kmsg_dump handlers they really
weren't safe in a crash dump scenario we should just remove it.

Eric
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