linux-kernel - Re: [Xen-devel] [PATCH 3/3] xen/pv-on-hvm kexec+kdump: reset PV devices in kexec or crash kernel

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Message-ID: <20110809094443.GD7283@aepfle.de>
Date:	Tue, 9 Aug 2011 11:44:43 +0200
From:	Olaf Hering <olaf@...fle.de>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Konrad <konrad.wilk@...cle.com>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>
Subject: Re: [Xen-devel] [PATCH 3/3] xen/pv-on-hvm kexec+kdump: reset PV
 devices in kexec or crash kernel

On Tue, Aug 09, Ian Campbell wrote:

> >  static int frontend_probe_and_watch(struct notifier_block *notifier,
> >  				   unsigned long event,
> >  				   void *data)
> >  {
> > +	/* reset devices in Connected or Closed state */
> > +	if (xen_hvm_domain())
>                                && reset_devices ??

No, reset_devices is passed as kernel cmdline option to a kdump boot.
But its not part of a kexec boot.

> How long should we wait for the backend to respond? Should we add a
> timeout and countdown similar to wait_for_devices?

Adding a timeout to catch a confused backend is a good idea. That would
give one at least a chance to poke around in a rescue shell.

> It's unfortunate that this code is effectively serialising on each
> device. It would be much preferable to kick off all the resets and then
> wait for them to occur. You could probably do this by incrementing a
> counter for each device you reset and decrementing it each time a watch
> triggers then wait for the counter to hit zero.

That feature needs more thought. Since xenbus_reset_state() is only
executed in the kexec/kdump case, the average use case is not slowed
down.

Olaf
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