linux-kernel - RE: [RFC][PATCH -mmotm 0/4] Improvement of pstore/kmsg

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Message-ID: <5C4C569E8A4B9B42A84A977CF070A35B2C199C6AAD@USINDEVS01.corp.hds.com>
Date:	Wed, 20 Jul 2011 18:34:13 -0400
From:	Seiji Aguchi <seiji.aguchi@....com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Americo Wang <xiyou.wangcong@...il.com>,
	Matthew Garrett <mjg@...hat.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jarod Wilson <jwilson@...hat.com>,
	"hpa@...or.com" <hpa@...or.com>,
	"dzickus@...hat.com" <dzickus@...hat.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH -mmotm 0/4] Improvement of pstore/kmsg_dump in
 kexec/panic path

Hi Vivek,

> Why can't we log something in user space when user initiates a reboot,
> Why does kernel need to capture that info in NVRAM.

 As I explained in following thread, 
 customers sometimes ask us to investigate the reason why system reboots.
 
 https://lkml.org/lkml/2010/11/17/249
 
 We can solve following scenario by logging messages in kernel space.

  - Syslogd is killed by mistake.
    (user kills syslogd with command or other applications send signal).
  - And then, system reboots.

 If we log messages in user space, we can't see messages.

Seiji

>-----Original Message-----
>From: Vivek Goyal [mailto:vgoyal@...hat.com]
>Sent: Tuesday, July 19, 2011 2:48 PM
>To: Seiji Aguchi
>Cc: kexec@...ts.infradead.org; linux-kernel@...r.kernel.org; linux-mtd@...ts.infradead.org; Eric W. Biederman; KOSAKI
>Motohiro; Americo Wang; Matthew Garrett; tony.luck@...el.com; Andrew Morton; Jarod Wilson; hpa@...or.com;
>dzickus@...hat.com; dle-develop@...ts.sourceforge.net; Satoru Moriya
>Subject: Re: [RFC][PATCH -mmotm 0/4] Improvement of pstore/kmsg_dump in kexec/panic path
>
>On Tue, Jul 19, 2011 at 02:23:26PM -0400, Seiji Aguchi wrote:
>> Hi,
>>
>> [Upstream status]
>>    Discussion about kmsg_dump() in kdump path:
>>     - Eric and Vivek are worried about reliability of existing kmsg_dump().
>>     - Especially, Vivek would like to remove a RCU  function call chain in kdump path
>> 　　　 which kernel modules can register their function calls freely.
>>
>>    Discussion about pstore in nmi_hander.
>>     - Don Zickus found an issue of pstore in nmi_handler due to its mutex_lock.
>
>You did not answer my questions in the last posting mail thread and gone
>ahead with the new posting. How are we supposed to discuss something. This
>has been a problem on this mail thread since the beginneing. There is
>little open discussion.
>
>So if you want to make any progress in this direction, what will help
>is open discussion.
>
>Locking is going to be a problem. So atleast we can remove kmsg_dump()
>infrastructure from reboot path. Why can't we log something in user
>space when user initiates a reboot, let it get logged in /var/log/messages
>and then umount the file root and go ahead with reboot. Why does kernel
>need to capture that info in NVRAM.
>
>If we can get rid of all the logging thing on reboot path, then at least
>it does not need to be lock protected with crash path.
>
>Thanks
>Vivek