RE: [RFC][PATCH -mmotm 0/4] Improvement of pstore/kmsg_dump inkexec/panic path

From: Seiji Aguchi
Date: Wed Jul 20 2011 - 18:35:15 EST

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.

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.


>-----Original Message-----
>From: Vivek Goyal [mailto:vgoyal@xxxxxxxxxx]
>Sent: Tuesday, July 19, 2011 2:48 PM
>To: Seiji Aguchi
>Cc: kexec@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-mtd@xxxxxxxxxxxxxxxxxxx; Eric W. Biederman; KOSAKI
>Motohiro; Americo Wang; Matthew Garrett; tony.luck@xxxxxxxxx; Andrew Morton; Jarod Wilson; hpa@xxxxxxxxx;
>dzickus@xxxxxxxxxx; dle-develop@xxxxxxxxxxxxxxxxxxxxx; 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
>> ããã 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.
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