linux-kernel - Re: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler"

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Date:	Mon, 20 Jul 2009 12:22:57 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Neil Horman <nhorman@...driver.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	Brayan Arraes <brayan@...k.com.br>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler"

Lai Jiangshan <laijs@...fujitsu.com> writes:

> 1) This fix breaks our tools.
>       This fix changes the ABI. panic_on_oops is default 0,
>    and a lots system do not specify the boot option "panic",
>    thus, Sysrq-c will not cause CrashDump(Kdump) as expected.

How does it break your tools?

> 2) When CONFIG_KEXEC=n, Sysrq-c should become an invalid
>    command like Sysrq-D(CONFIG_LOCKDEP, show-all-locks).
>    But this fix makes it a valid command and let it do a
>    hazard thing: cause a page fault(NULL dereference) in kernel.
>
> So, we revert this fix.

The idea was to extend sysrq-d to also be a way of testing NULL
pointer dereferences.  How is that a bad idea?

Eric
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