linux-kernel - Re: [PATCH] xen/pci: Deal with toolstack missing an 'XenbusStateClosing'.

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Date:	Wed, 12 Jun 2013 09:45:04 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	George Dunlap <george.dunlap@...citrix.com>
Cc:	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] xen/pci: Deal with toolstack missing an
 'XenbusStateClosing'.

On Tue, Jun 11, 2013 at 05:17:45PM +0100, George Dunlap wrote:
> On 06/11/2013 05:08 PM, konrad wilk wrote:
> >
> >On 6/11/2013 11:36 AM, George Dunlap wrote:
> >>On 06/10/2013 10:06 PM, Konrad Rzeszutek Wilk wrote:
> >>>There are two tool-stack that can instruct the Xen PCI frontend
> >>>and backend to change states: 'xm' (Python code with a daemon),
> >>>and 'xl' (C library - does not keep state changes).
> >>>
> >>>With the 'xm', the path to disconnect a PCI device (xm pci-detach
> >>><guest> <BDF>)is:
> >>>
> >>>4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)->
> >>>4(Connected)->5(Closing*).
> >>>
> >>>The * is for states that the tool-stack sets. For 'xl', it is similar:
> >>>
> >>>4(Connected)->7(Reconfiguring*)-> 8(Reconfigured)-> 4(Connected)
> >>>
> >>>Both of them also tear down the XenBus structure, so the backend
> >>>state ends up going in the 3(Initialised) and calls
> >>>pcifront_xenbus_remove.
> >>
> >>So I looked a little bit into this; there are actually two different
> >>states that happen as part of this handshake.  In order to disonnect a
> >>*device*, xl signals using the *bus* state, like this:
> >>* Wait for the *bus* to be in state 4(Connected)
> >>* Set the *device* state to 5(Closing)
> >>* Set the *bus* state to 7(Reconfiguring)
> >>* Wait for the *bus* state to return to 4(Connected)
> >>
> >>So are all of these states you see the *bus* state?  And why would you
> >>disconnect the whole pci bus if you're only removing one device?
> >
> >Correct. The stats I enumerated are *bus* states. Not per-device states.
> >I presume (and I hadn't checked xm) that Xend has some logic to only
> >disconnect the bus if all of the PCI devices have been disconnected. In
> >'xl' it does not do that.
> >
> >The testing I did was just with one PCI device.
> 
> Ah, OK -- I see now.  The problem is that the code in the Linux side
> didn't know about the whole "4->7->8->4" thing to unplug a device.
> In all likelihood, if you had used xm with two devices (so that the
> bus didn't get disconnected), then you would have run across the
> same error.
> 
> So at least part of the problem *is* a bug in Linux.

Good! Bjorn, would you be OK Ack-ing the patch I sent (attached here
for reference) or putting it in your queue for Linus?

My plan would be to send it to Linus in the 3.11 merge window.

View attachment "0001-xen-pci-Deal-with-toolstack-missing-an-XenbusStateCl.patch" of type "text/plain" (3106 bytes)