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: <1312889194.26263.107.camel@zakaz.uk.xensource.com>
Date:	Tue, 9 Aug 2011 12:26:34 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	Olaf Hering <olaf@...fle.de>
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, 2011-08-09 at 10:44 +0100, Olaf Hering wrote:
> 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.

I was thinking more of avoiding slowing down the kexec/kdump case
unnecessarily.

Ian.
> 
> Olaf


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