linux-kernel - Re: [Q] Why does kexec use device

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Message-ID: <1389938353.7406.22.camel@pasglop>
Date:	Fri, 17 Jan 2014 16:59:13 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	Vivek Goyal <vgoyal@...hat.com>, kexec@...ts.infradead.org
Subject: Re: [Q] Why does kexec use device_shutdown rather than ubind them

On Thu, 2014-01-16 at 20:52 -0800, Eric W. Biederman wrote:
> 
> I think we have largely survied until now because kdump is so popular
> and kdump winds up having to reinitialize devices from any random
> state.

kdump also doesn't care too much if the device is still DMA'ing to the
old kernel memory :-)

> But like I said I am all for reducing the burden on device driver
> developers.

Right. I'm experimenting with a variant of device_shutdown() that tries
remove() first and if it doesn't exist and shutdown() does, call that
(is that ever the case ?). I'm keeping this kexec-specific for now.

I'll try to hammer that on some of our machines see if it breaks
anything, I think it's a much better approach for kexec.

As for actual machine shutdown, we *might* have some corner cases where
shutdown is actually different from remove for good reasons, so that
will have to be investigated a bit more in depth.

I'll post my results when I have them.

Cheers,
Ben.

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