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

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Message-ID: <20160530193742.GA15011@merlins.org>
Date:	Mon, 30 May 2016 12:37:42 -0700
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 Thu, Mar 10, 2016 at 09:13:13PM -0800, Marc MERLIN wrote:
> 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.

Just updated to 4.6 and re-applied Eric sysrq patch.
It's saved me many times already. I absolutely need to do clean reboots
for both my software raid and bcache, and when the system is not doing
well, sysrq-o does the graceful shutdown, but also powers off my server,
which is not what I want.
I've been using the new sysrq-x Eric wrote and it's been working great.

Any chance, we can get this into standard kernels? I can't be the only
person who benefits from this...
Any suggestion on who might be a good person to
review/critique/integrate this patch?

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