Re: [Xen-devel] [PATCH v5] Fixes to Xen pciback for 3.17.

[Sander Eikelenboom]

Tuesday, August 5, 2014, 4:04:43 PM, you wrote:


> Tuesday, August 5, 2014, 3:49:30 PM, you wrote:

>> On Tue, Aug 05, 2014 at 11:44:33AM +0200, Sander Eikelenboom wrote:
>>> 
>>> Tuesday, August 5, 2014, 11:31:08 AM, you wrote:
>>> 
>>> > On 05/08/14 09:44, Sander Eikelenboom wrote:
>>> >> 
>>> >> Monday, August 4, 2014, 8:43:18 PM, you wrote:
>>> >> 
>>> >>> On Fri, Aug 01, 2014 at 04:30:05PM +0100, David Vrabel wrote:
>>> >>>> On 14/07/14 17:18, Konrad Rzeszutek Wilk wrote:
>>> >>>>> Greg: goto GHK
>>> >>>>>
>>> >>>>> This is v5 version of patches to fix some issues in Xen PCIback.
>>> >>>>
>>> >>>> Applied to devel/for-linus-3.17.
>>> >> 
>>> >>> Thank you.
>>> >>>>
>>> >>>> I dropped the stable Cc for #2 pending a final decision on whether it
>>> >>>> really is a stable candidate.
>>> >> 
>>> >>> OK.
>>> >>>>
>>> >>>> David
>>> >> 
>>> >> Hi Konrad / David,
>>> >> 
>>> >> This series still lacks a resolution on the sysfs /do_flr /reset,
>>> >> as a result the pci devices are not reset after shutdown of a guest.
>>> >> (no more pciback 0000:xx:xx.x: restoring config space at offset xxx)
>>> >> 
>>> >> So this series now introduces a regression to 3.16, which causes devices to malfunction 
>>> >> after a guest reboot or after assigning the devices to another guest.
>>> 
>>> > I don't follow what you're saying.  The lack of a device reset for PCI
>>> > devices with no FLR method isn't a regression as this has never worked.
>>> >  Can you explain in more detail what the regression is and which patch
>>> > caused it?
>>> 
>>> I haven't bisected it to a specific patch in this series,
>>> but this patch series (when pulled on top of 3.16) cause the following:
>>> 
>>> - Do a system start and HVM guest start
>>> - HVM guest with pci passthrough, devices work fine
>>> - shutdown the HVM guest
>>> - "pciback 0000:xx:xx.x: restoring config space at offset xxx" messages do not
>>>   appear anymore when shutting down the HVM guest (as they do with vanilla 3.16)
>>> - Starting the HVM guest again with the same devices passed through.
>>> - Devices malfunction (for example a USB host controller will fail a simple 
>>>   "lsusb"
>>> - And this all works fine on vanilla 3.16.  

>> Hm, the only patch that makes code changes is 63fc5ec97cc54257d1c4ee49ed2131f754a5ff9b
>> "xen/pciback: Don't deadlock when unbinding."
>> but it does not change any of that code path. Only figures out whether
>> to take a lock or not.

> Ok and the do_flr nack by david is unrelated to this part (i didn't check just 
> assumed there could be a connection)

>> I will try it out on my box and see if I can reproduce it.

>> And just to be 100% sure - you are using vanilla Xen? No changes on top
>> of it?

> Except the fix from jan for the pirq/msi stuff (and an unrelated hpet one), other than that no.
> If you can't reproduce i will see if i can dive deeper into it tonight !

Hi Konrad,

It looks like the issues is this part of the change:

    --- a/drivers/xen/xen-pciback/pci_stub.c
    +++ b/drivers/xen/xen-pciback/pci_stub.c
    @@ -250,6 +250,8 @@ struct pci_dev *pcistub_get_pci_dev(struct xen_pcibk_device *pdev,
    * - 'echo BDF > unbind' with a guest still using it. See pcistub_remove
    *
    * As such we have to be careful.
    + *
    + * To make this easier, the caller has to hold the device lock.
    */
    void pcistub_put_pci_dev(struct pci_dev *dev)
    {
    @@ -276,11 +278,8 @@ void pcistub_put_pci_dev(struct pci_dev *dev)
    /* Cleanup our device
    * (so it's ready for the next domain)
    */
    -
    - /* This is OK - we are running from workqueue context
    - * and want to inhibit the user from fiddling with 'reset'
    - */
    - pci_reset_function(dev);
    + lockdep_assert_held(&dev->dev.mutex);
    + __pci_reset_function_locked(dev);
    pci_restore_state(dev);
   /* This disables the device. */

More specifically:
The old "pci_reset_function(dev)" potentially seems to do much more than 
__pci_reset_function_locked(dev).


"__pci_reset_function_locked(dev)" only calls  "__pci_dev_reset"
while "pci_reset_function" not only calls pci_dev_reset, but on succes
it also calls: "pci_dev_save_and_disable" which does a save state etc.


So i added a little more debug:

device_lock_assert(&dev->dev);
ret = __pci_reset_function_locked(dev);
dev_dbg(&dev->dev, "%s __pci_reset_function_locked:%d  dev->state_saved:%d\n", __func__, ret, (!dev->state_saved) ? 0 : 1 );
pci_restore_state(dev);

And this returns:
[  494.570579] pciback 0000:04:00.0: pcistub_put_pci_dev __pci_reset_function_locked:0  dev->state_saved:0

So that confirms there is no saved_state to get restored by 
pci_restore_state(dev) in the next line.

However there seems to be no "locked" variant of the function 
"pci_reset_function" in pci.c that has all the same logic ...

--
Sander 

>> Thanks!

>>> 
>>> >> Apart from that .. i can't resist to remind the other issue with removing pci
>>> >> devices passed through to HVM guests related to the signaling via xenstore,
>>> >> described in:
>>> >> 
>>> >> http://lists.xen.org/archives/html/xen-devel/2014-07/msg01875.html
>>> 
>>> > I don't remember seeing you posting a patch...?

>> I was going to, but I think we need to figure out the 'do_flr' mechanism
>> first.

>>> 
>>> > David
>>> 
>>> 





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