Re: [Xen-devel] Please apply "partially revert "xen: Remove event channel..."

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 04/10/2017 09:57 AM, Juergen Gross wrote:
> On 10/04/17 15:47, Boris Ostrovsky wrote:
>> On 04/07/2017 06:11 PM, Stefano Stabellini wrote:
>>> On Fri, 7 Apr 2017, Boris Ostrovsky wrote:
>>>> On 04/07/2017 01:36 PM, Stefano Stabellini wrote:
>>>>> On Fri, 7 Apr 2017, Boris Ostrovsky wrote:
>>>>>> On 04/07/2017 07:58 AM, Ian Jackson wrote:
>>>>>>> tl;dr:
>>>>>>>  Please apply
>>>>>>>
>>>>>>>     da72ff5bfcb02c6ac8b169a7cf597a3c8e6c4de1
>>>>>>>     partially revert "xen: Remove event channel notification through
>>>>>>>       Xen PCI platform device"
>>>>>>>
>>>>>>>  to all stable branches which have a version of the original broken
>>>>>>>  commit.  This includes at least 4.9.y.
>>>>>>>
>>>>>>> Background:
>>>>>>>
>>>>>>> osstest service owner writes ("[linux-4.9 baseline test] 107238: 
>>>>>>> tolerable FAIL"):
>>>>>>> ...
>>>>>>>>  test-amd64-amd64-qemuu-nested-intel 13 xen-boot/l1  fail never pass
>>>>>>> osstest doesn't consider this a regresion because it looks for
>>>>>>> regressions within a branch, and this is the first test of Linux 4.9.
>>>>>>> However, this is a regression from the kernel we are currently using.
>>>>>>>
>>>>>>> L1 dom0 console log:
>>>>>>>   
>>>>>>> http://logs.test-lab.xenproject.org/osstest/logs/107238/test-amd64-amd64-qemuu-nested-intel/huxelrebe0---var-log-xen-osstest-serial-l1.guest.osstest.log
>>>>>>>
>>>>>>> It seems to have got stuck halfway through booting.
>>>>>>>
>>>>>>> The message
>>>>>>>   (XEN) *** Serial input -> Xen (type 'CTRL-x' three times to switch 
>>>>>>> input to DOM0)
>>>>>>> shows where osstest timed out on this test, and started its log
>>>>>>> capture process (including collecting debug key output).
>>>>>>>
>>>>>>> Complete logs for this job here:
>>>>>>>   
>>>>>>> http://logs.test-lab.xenproject.org/osstest/logs/107238/test-amd64-amd64-qemuu-nested-intel/info.html
>>>>>>>
>>>>>>> Juergen Gross tells me that this is due to the lack of
>>>>>>> da72ff5bfcb02c6ac8b169a7cf597a3c8e6c4de1.
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Ian.
>>>>>>>
>>>>>>> PS: Stefano, Boris: did you already request a backport of this commit?
>>>>>>> If not, why not ?
>>>>>> No, but this should indeed be backported to 4.9+
>>>>> Boris, are you going to do that?
>>>> Is there anything that needs to be done beyond just applying it to 4.9
>>>> (4.10 apparently already has it).
>>> No, I don't think so. 4.9 already has the offending commit.
>>
>> Looks like there will be a new version of the original patch
>> (72a9b186292) so we should hold off with backport request to 4.9:
>>
>> https://lists.xenproject.org/archives/html/xen-devel/2017-04/msg01468.html
> TBH: I'm not convinced by the reasoning why 72a9b186292 has to be
> reworked: Do we really care for Xen versions < 4.0 and a theoretical
> problem (after all the author admitted the bug isn't being hit in
> reality due to a short-circuit in the code)?

I don't know what the deal is with <4.0 Xen and I am not sure whether we
can boot new-ish Linux on those releases regardless of this specific
issue. I am certainly only testing Xen 4.1+ and have been doing this for
at least last 2-3 years.


>
> And even if we do: I'd rather add another patch to stable later than
> keeping a real bug in Linux 4.9 which has been hit at least 3 times
> up to now (by Stefano, George and Ian).

That would depend on how soon the new patch shows up.

-boris

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