Re: [Xen-devel] Xen pci-passthrough problem with pci-detach and pci-assignable-remove

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Feb 20, 2014 at 05:18:46PM +0100, Sander Eikelenboom wrote:
> 
> Thursday, February 20, 2014, 9:53:59 AM, you wrote:
> 
> 
> > Friday, January 24, 2014, 6:48:06 PM, you wrote:
> 
> >> On Fri, Jan 24, 2014 at 02:36:02PM +0100, Sander Eikelenboom wrote:
> >>> 
> >>> Friday, January 10, 2014, 6:38:10 PM, you wrote:
> >>> 
> >>> >> > Wow. You just walked in a pile of bugs didn't you? And on Friday
> >>> >> > nonethless.
> >>> >> 
> >>> >> As usual ;-)
> >>> 
> >>> > Ha!
> >>> > ..snip..
> >>> >> >> [  489.082358]  [<ffffffff81087ac6>] ? mutex_spin_on_owner+0x38/0x45
> >>> >> >> [  489.106272]  [<ffffffff818e5e22>] ? 
> >>> >> >> schedule_preempt_disabled+0x6/0x9
> >>> >> >> [  489.130158]  [<ffffffff818e7034>] ? 
> >>> >> >> __mutex_lock_slowpath+0x159/0x1b5
> >>> >> >> [  489.154147]  [<ffffffff818e70a6>] ? mutex_lock+0x16/0x25
> >>> >> >> [  489.177890]  [<ffffffff8135972d>] ? pci_reset_function+0x26/0x4e
> >>> >> 
> >>> >> > Yeah, that bug my RFC patchset (the one that does the slot/bus 
> >>> >> > reset) should also fix.
> >>> >> > I totally forgot about it !
> >>> >> 
> >>> >> Got a link to that patchset ?
> >>> 
> >>> > https://lkml.org/lkml/2013/12/13/315
> >>> 
> >>> >> I at least could give it a spin .. you never know when fortune is on 
> >>> >> your side :-)
> >>> 
> >>> > It is also at this git tree:
> >>> 
> >>> > git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git and the
> >>> > branch name is "devel/xen-pciback.slot_and_bus.v0". You will likely
> >>> > want to merge it in your current Linus tree.
> >>> 
> >>> > Thank you!
> >>> 
> >>> 
> >>> Hi Konrad,
> >>> 
> >>> Just got time to test this some more, when merging this branch *except* 
> >>> the last commit (9599a5ad38a3bb250e996ccb2cdaab6fb68aaacd)
> >>> seems to help with my problem,i'm no capable of using:
> >>> - xl pci-detach
> >>> - xl pci-assignable-remove
> >>> - echo "BDF" > /sys/bus/pci/drivers/<devicename>/bind
> >>> 
> >>> to remove a pci device from a running HVM guest and rebinding it to a 
> >>> driver in dom0 without those nasty stacktraces :-)
> >>> So the first 4 seem to be an improvement.
> >>> 
> >>> That last commit (9599a5ad38a3bb250e996ccb2cdaab6fb68aaacd) seems to give 
> >>> troubles of it's own.
> 
> >> Could you email me your lspci output and also which devices you 
> >> move/switch etc?
> 
> > Hi Konrad,
> 
> > At the moment i found some time to figure out what goes wrong with the xl 
> > pci-detach and xl pci-assignable-remove, i have been
> > able to narrow it down a bit:
> 
> > The problem only occurs when you:
> > - passthrough 2 (or more?) pci devices assigned to a guest ..
> > - and only remove 1 of those devices with "xl pci-detach" followed by a "xl 
> > pci-assignable-remove"
> > - when you first detach both devices with "xl pci-detach" before doing the 
> > "xl pci-assignable-remove" it works ok.
> 
> > In my case i'm passingthrough 2 devices (02:00.0 and 00:19.0)
> 
> > I added some printk's and what i found out is that:
> > - after doing the pci-detach of 02:00.0, it doesn't call 
> > pcistub_put_pci_dev for that device ...
> > - but when i subsequently pci-detach the second (and last) device 00:19.0 
> > .. it does call it for both 02:00.0 and 00:19.0 ...
> > - so somehow that call for the first detached device gets deferred .. but 
> > since it are different devices and not functions of the same device i don't
> >   see any reason for it to wait until all other devices would have been 
> > detached ...
> 
> 
> > I tried to capture the console output but some how that didn't work out, so 
> > i attached a screenshot of what happens when:
> > - doing a xl pci-list for the guest
> > - doing a xl pci-assignable-list
> 
> > - doing the xl pci-detach for 02:00.0
> 
> > - doing a xl pci-list for the guest
> > - doing a xl pci-assignable-list
> 
> > - waiting some time ...
> 
> > - doing the xl pci-detach for 00:19.0
> 
> > - doing a xl pci-list for the guest
> > - doing a xl pci-assignable-list
> 
> > There you can see this strange sequence of events :-)
> 
> > But i haven't been able to spot the culprit
> 
> Enabled some extra debugging and added some more printk's .. (see new 
> screenshot)
> 
> From what it seems .. the frontend state for the first device isn't changed 
> on the first pci-detach ..
> 
> Is the signaling on pci-detach the guests (pcifront) responsibility or the 
> toolstacks (libxl) ?

It usually is pcifront. And in the screenshot I see:

.. frontend is gone! unregister device

which should trigger the process. And it does look to do that.

Hm, I am wondering what the toolstack is waiting for.

Time to debug.
> 
> 
> 
> > attached: screenshot.jpg

and thanks for the screenshot (didn't have copy-n-paste option handy :-))

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