Re: [PATCH] scsi: lpfc: Add shutdown method for kexec

From: Brian King <brking@linux.vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Anton Blanchard <anton@samba.org>
Cc: james.smart@broadcom.com, dick.kennedy@broadcom.com,
	jejb@linux.vnet.ibm.com, martin.petersen@oracle.com,
	jk@ozlabs.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH] scsi: lpfc: Add shutdown method for kexec
Date: Mon, 13 Feb 2017 15:57:22 -0600	[thread overview]
Message-ID: <2fa7fc70-44d4-f536-befb-8a7849741fb7@linux.vnet.ibm.com> (raw)
In-Reply-To: <1486947669.3401.69.camel@kernel.crashing.org>

On 02/12/2017 07:01 PM, Benjamin Herrenschmidt wrote:
> On Mon, 2017-02-13 at 13:21 +1300, Eric W. Biederman wrote:
>>> Good point, at the very least we should call remove if shutdown doesn't
>>> exist. Eric: could we make the changes Ben suggests?
>>
>> Definitely.  That was the original design of the kexec interface
>> but people were worried about calling remove during reboot might
>> introduce regressions on the reboot functionality.  So shutdown was
>> added to be remove without the cleaning up the kernel data structures.
> 
> Right. Part of the problem was also that remove was dependent on CONFIG_HOTPLUG
> though that's no longer the case anymore.
> 
> The problem is that a bunch of drivers either don't have a shutdown or
> worse, have one that actually shuts the HW down rather than "idle" it
> which puts it in a state that the new kernel can't deal with.

If we do transition to use remove rather than shutdown, I think we want
some way for a device driver to know whether we are doing kexec or not.
A RAID adapter with a write cache is going to want to flush its write
cache on a PCI hotplug remove, but for a kexec, its going to want to skip
that so the kexec is faster. Today, since kexec looks like a reboot,
rather than a shutdown, we can skip the flush on a reboot, since its
technically not needed there either.

-Brian

-- 
Brian King
Power Linux I/O
IBM Linux Technology Center