linux-kernel - Re: [PATCH-RFC]: sysrq-a: graceful reboot via kernel

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Message-ID: <20160311051313.GF26973@merlins.org>
Date:	Thu, 10 Mar 2016 21:13:13 -0800
From:	Marc MERLIN <marc@...lins.org>
To:	Eric Wheeler <linux-kernel@...ts.ewheeler.net>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH-RFC]: sysrq-a: graceful reboot via kernel_restart(),
 similar to sysrq-o

On Fri, Mar 11, 2016 at 04:35:21AM +0000, Eric Wheeler wrote:
> Hello all,
> 
> We were having a discussion on the bcache list about the safest reboot 
> options via sysrq here:
>   http://thread.gmane.org/gmane.linux.kernel.bcache.devel/3559/focus=3586
> 
> The result of the discussion ended up in a patch for sysrq-a to call 
> kernel_restart much in the same way as sysrq-ocalls kernel_power_off.
> 
> Please comment on the patch and suggest any appropriate changes.  

Thanks Eric.

The quick rationale is that sysrq-r is not desirable  to use if you're using
bcache, or software raid since it will reboot without giving them a
chance to properly sync their buffers and get into a clean state.

I've been using sysrq-o to get a clean shutdown, but of course that
actually powers off the server, and you then need to rely on something
like WOL to bring the machine back up, which isn't always easy or
possible.

This new reboot with proper flushing (kernel_power_off) allows for safe
reboots that don't upset bcache or software raid.

Thanks,
Marc
-- 
"A mouse is a device used to point at the xterm you want to type in" - A.S.R.
Microsoft is to operating systems ....
                                      .... what McDonalds is to gourmet cooking
Home page: http://marc.merlins.org/                         | PGP 1024R/763BE901