linux-kernel - Re: [Patch] kexec: remove KMSG_DUMP_KEXEC (was Re: Query about kdump_msg hook into crash

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Date:	Tue, 1 Feb 2011 10:28:45 -0500
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	kosaki.motohiro@...fujitsu.com,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Jarod Wilson <jwilson@...hat.com>, akpm@...ux-foundation.org,
	Simon Kagstrom <simon.kagstrom@...insight.net>,
	David Woodhouse <David.Woodhouse@...el.com>
Subject: Re: [Patch] kexec: remove KMSG_DUMP_KEXEC (was Re: Query about
 kdump_msg hook into crash_kexec())

On Tue, Feb 01, 2011 at 04:13:13PM +0800, Américo Wang wrote:
> On Tue, Feb 01, 2011 at 03:38:53PM +0800, Américo Wang wrote:
> >On Mon, Jan 31, 2011 at 11:33:15PM -0800, Eric W. Biederman wrote:
> >>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.
> >>
> >
> >Probably, I think we need to get rid of KMSG_DUMP_KEXEC.
> >
> 
> Here we go.
> 
> --------->
> 
> KMSG_DUMP_KEXEC is useless because we already save kernel messages
> inside /proc/vmcore, and it is unsafe to allow modules to do
> other stuffs in a crash dump scenario.
> 

I think this is right thing to do. First of all kmsg_dump() call inside
crash_kexec() does not make any sense. Secondly, if kdump kernel is
loaded, we anyway are going to capture log buffers in vmcore and there
should not be any need to try to save messages twice.

Now one can argue that what if kdump does not capture the dump. I think
then right solution (though painful one) is to try to make kdump as
reliable as possible instead of trying to come up with backup mechanisms
to save logs in case kdump fails.

Acked-by: Vivek Goyal <vgoyal@...hat.com>

Thanks
Vivek

> Reported-by: Vivek Goyal <vgoyal@...hat.com>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Signed-off-by: WANG Cong <xiyou.wangcong@...il.com>
> 
> 
> ---
> diff --git a/drivers/char/ramoops.c b/drivers/char/ramoops.c
> index 1a9f5f6..8653ba4 100644
> --- a/drivers/char/ramoops.c
> +++ b/drivers/char/ramoops.c
> @@ -69,8 +69,7 @@ static void ramoops_do_dump(struct kmsg_dumper *dumper,
>  	struct timeval timestamp;
>  
>  	if (reason != KMSG_DUMP_OOPS &&
> -	    reason != KMSG_DUMP_PANIC &&
> -	    reason != KMSG_DUMP_KEXEC)
> +	    reason != KMSG_DUMP_PANIC)
>  		return;
>  
>  	/* Only dump oopses if dump_oops is set */
> diff --git a/drivers/mtd/mtdoops.c b/drivers/mtd/mtdoops.c
> index e3e40f4..56eac4e 100644
> --- a/drivers/mtd/mtdoops.c
> +++ b/drivers/mtd/mtdoops.c
> @@ -308,8 +308,7 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
>  	char *dst;
>  
>  	if (reason != KMSG_DUMP_OOPS &&
> -	    reason != KMSG_DUMP_PANIC &&
> -	    reason != KMSG_DUMP_KEXEC)
> +	    reason != KMSG_DUMP_PANIC)
>  		return;
>  
>  	/* Only dump oopses if dump_oops is set */
> diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
> index 2a0d7d6..05fa2a9 100644
> --- a/include/linux/kmsg_dump.h
> +++ b/include/linux/kmsg_dump.h
> @@ -17,7 +17,6 @@
>  enum kmsg_dump_reason {
>  	KMSG_DUMP_OOPS,
>  	KMSG_DUMP_PANIC,
> -	KMSG_DUMP_KEXEC,
>  	KMSG_DUMP_RESTART,
>  	KMSG_DUMP_HALT,
>  	KMSG_DUMP_POWEROFF,
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index ec19b92..3ac0218 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -32,7 +32,6 @@
>  #include <linux/console.h>
>  #include <linux/vmalloc.h>
>  #include <linux/swap.h>
> -#include <linux/kmsg_dump.h>
>  
>  #include <asm/page.h>
>  #include <asm/uaccess.h>
> @@ -1078,8 +1077,6 @@ void crash_kexec(struct pt_regs *regs)
>  		if (kexec_crash_image) {
>  			struct pt_regs fixed_regs;
>  
> -			kmsg_dump(KMSG_DUMP_KEXEC);
> -
>  			crash_setup_regs(&fixed_regs, regs);
>  			crash_save_vmcoreinfo();
>  			machine_crash_shutdown(&fixed_regs);
--
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