linux-kernel - Re: [PATCH] kdump: Enable kdump if 2nd-kernel is loaded.

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Message-ID: <4A56E069.5040907@jp.fujitsu.com>
Date:	Fri, 10 Jul 2009 15:32:09 +0900
From:	Hidetoshi Seto <seto.hidetoshi@...fujitsu.com>
To:	"Ken'ichi Ohmichi" <oomichi@....nes.nec.co.jp>
CC:	lkml <linux-kernel@...r.kernel.org>,
	kexec-ml <kexec@...ts.infradead.org>
Subject: Re: [PATCH] kdump: Enable kdump if 2nd-kernel is loaded.

Hi Ohmichi-san,

Ken'ichi Ohmichi wrote:
> Hi,
> 
> This patch enables a kdump if 2nd-kernel is loaded.
> (The patch is based on linux-2.6.31-rc2.)
> 
> Now, a kdump is enabled if a kernel parameter "oops=panic" is specified and
> 2nd-kernel is loaded. I think that a kdump should be enabled regardless of
> "oops=panic" if 2nd-kernel is loaded, because a system administrator loads
> 2nd-kernel for enabling a kdump.

I think this description is slightly wrong because kdump will be invoked
from panic, regardless of the panic_on_oops.

Maybe:
 A kdump on oops is enabled if a kernel parameter "oops=panic" ...
         ~~~~~~~

> 
> * Reference
>   The discussion about this patch
>   http://lists.infradead.org/pipermail/kexec/2009-July/003417.html

I'd like to quote your comment:

>> I tried to test a kdump on linux-2.6.31-rc1 *without* a kernel parameter
>> "oops=panic" by `echo c > /proc/sysrq-trigger`, but a kdump did not work
>> because a kdump, which is occurred by `echo c > /proc/sysrq-trigger`, has
>> been changed to a NULL pointer error instead of calling crash_kexec()
>> since linux-2.6.31-rc1.

So the real problem is that kdump is not triggered by the NULL pointer oops
if !panic_on_oops, isn't it?

It seems that you should report this trouble of sysrq-c as a regression.

> 
> 
> Thanks
> Ken'ichi Ohmichi
> 
> Signed-off-by: Ken'ichi Ohmichi <oomichi@....nes.nec.co.jp>
> Acked-by: Simon Horman <horms@...ge.net.au>
> ---
> --- a/kernel/kexec.c	2009-07-08 12:30:26.000000000 +0900
> +++ b/kernel/kexec.c	2009-07-08 12:38:08.000000000 +0900
> @@ -57,6 +57,8 @@ struct resource crashk_res = {
>  
>  int kexec_should_crash(struct task_struct *p)
>  {
> +	if (kexec_crash_image)
> +		return 1;
>  	if (in_interrupt() || !p->pid || is_global_init(p) || panic_on_oops)
>  		return 1;
>  	return 0;

I think kexec cannot crash if there is no image, right?

Then:

 if (kexec_crash_image)
 	return 1;
 return 0;

or

 return (kexec_crash_image) ? 1 : 0;

or

 since crash_kexec() is nop if !kexec_crash_image,
 replace all:
   if (kexec_should_crash(p))
   	crash_kexec(reg);
 at everywhere in kernel to a simple line:
   crash_kexec(reg);
 and remove kexec_should_crash() completely

would be better fix.


Thanks,
H.Seto

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