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SubjectRe: [PATCH] sysrq, kdump: fix regression, revert "simplify sysrq-c handler"
Lai Jiangshan wrote:
> 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.
>
> 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.
>
> |commit d6580a9f15238b87e618310c862231ae3f352d2d
> |Author: Neil Horman <nhorman@tuxdriver.com>
> |Date: Wed Jun 17 16:28:17 2009 -0700
>
> | kexec: sysrq: simplify sysrq-c handler
>
> | Currently the sysrq-c handler is bit over-engineered. Its behavior is
> | dependent on a few compile time and run time factors that alter its
> | behavior which is really unnecessecary.
>
> | If CONFIG_KEXEC is not configured, sysrq-c, crashes the system with a NULL
> | pointer dereference. If CONFIG_KEXEC is configured, it calls crash_kexec
> | directly, which implies that the kexec kernel will either be booted (if
> | its been previously loaded), or it will simply do nothing (the no kexec
> | kernel has been loaded).
>
> | It would be much easier to just simplify the whole thing to dereference a
> | NULL pointer all the time regardless of configuration. That way, it will
> | always try to crash the system, and if a kexec kernel has been loaded into
> | reserved space, it will still boot from the page fault trap handler
> | (assuming panic_on_oops is set appropriately).
>
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> ---

FYI, this problem has already pointed by Ohmichi-san and this will be an
another patch for the following discussion:
http://lists.infradead.org/pipermail/kexec/2009-July/003433.html
You can find my sloppy memo in:
http://lists.infradead.org/pipermail/kexec/2009-July/003443.html

I agree with you that SysRq-'c' is well known as for 'C'rashdump, and it is
not expected as 'C'rash without dump.


Thanks,
H.Seto



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