linux-kernel - Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot

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Message-ID: <fff9e48d-e9a5-632d-5d84-a0aaa68f92a9@0882a8b5-c6c3-11e9-b005-00805fc181fe>
Date:   Sun, 28 Jun 2020 19:23:22 +0100
From:   Simon Arlott <simon@...iron.net>
To:     Damien Le Moal <Damien.LeMoal@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH] scsi: sd: stop SSD (non-rotational) disks before reboot

On 19/06/2020 00:31, Damien Le Moal wrote:
> On 2020/06/18 21:26, Simon Arlott wrote:
>> I haven't verified it, but the BIOS leaves the power off for several
>> seconds which should be long enough for the HDDs to spin down.
>> 
>> I'm less concerned about those suddenly losing power but it would be
>> nice to have a stop command sent to them too.
> 
> OK. So maybe the patch should be as simple as changing SYSTEM_RESTART state to
> SYSTEM_POWER_OFF if reboot=p is set, no ? Since that is consistent with the fact
> that reboot=p will cause power to go off, exactly the same as a regular
> shutdown, it seems cleaner and safer to use SYSTEM_POWER_OFF for the entire
> system, not just scsi disks.

That could be a bit misleading because the power isn't going to stay
off. Some of the network drivers have specific WOL behaviour changes
for a power off.

Power cycling the PSU is not something that every BIOS will do, so it's
not that simple. It could be a module parameter but I'd be concerned
that some other code will assuming the system should be powered off and
all of my reboots will become power off events.

-- 
Simon Arlott