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

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Date:	Wed, 12 Jun 2013 11:28:41 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc:	George Dunlap <george.dunlap@...citrix.com>,
	xen-devel <xen-devel@...ts.xensource.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] xen/pci: Deal with toolstack missing an 'XenbusStateClosing'.

On Wed, Jun 12, 2013 at 7:45 AM, Konrad Rzeszutek Wilk
<konrad.wilk@...cle.com> wrote:
> 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.

Sure; this is your baby :)  Why don't you handle it via your tree,
since it's more related to xen than any PCI core stuff.

Acked-by: Bjorn Helgaas <bhelgaas@...gle.com>
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