From mboxrd@z Thu Jan  1 00:00:00 1970
From: Marc MERLIN <marc@merlins.org>
Subject: Re: How can I ensure that my swraid saves checkpoints with sysrq reboot?
Date: Wed, 12 Sep 2012 14:52:36 -0700
Message-ID: <20120912215236.GL28054@merlins.org>
References: <20120912165208.GA12152@merlins.org> <20120913072944.06021ab6@notabene.brown>
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To: NeilBrown <neilb@suse.de>
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On Thu, Sep 13, 2012 at 07:29:44AM +1000, NeilBrown wrote:
> Hi Marc,
>=20
> md registers a reboot notifier.  When that is called it tries to checkpoi=
nt
> everything.
> All varieties of the 'reboot' system call seem to call the reboot notifie=
rs.
> alt-sysrq-b doesn't use the same path.  It calls machine_emergency_restar=
t,
> bypassing all the reboot handling.
>=20
> Once upon a time I had the idea that killing the md threads would lead to
> proper checkpointing, so alt-sysrq-I would do-the-right-thing.
> I'm not sure if it does though.
>=20
> But alt-sysrq-o (power off) seems to use the normal reboot handling and so
> works - as you noticed.  So that should always be safe and seems to be the
> only safe approach.

Thank you for confirming what I thought I saw.

For my specific case, I'll be ok because I have a controllable power supply,
but obviously for the hosted server case, this sucks since sending a
poweroff makes sure the machine won't come back.

Is there a chance you can contact whoever is responsible for the sysrq-b
codepath to make the right call so that you get a chance to sync arrays, or
should admins just know to use sysrq-i and then sysrq-r ?

Thanks,
Marc
--=20
"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 coo=
king
Home page: http://marc.merlins.org/ =20

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