Re: [Xen-devel] Guest soft lockups with "xen: make xen_qlock_wait() nestable"

[Sander Eikelenboom <linux@xxxxxxxxxxxxxx>]

On 08/11/18 11:18, Juergen Gross wrote:
> On 08/11/2018 10:57, Sander Eikelenboom wrote:
>> On 08/11/18 09:18, Juergen Gross wrote:
>>> On 08/11/2018 09:14, Sander Eikelenboom wrote:
>>>> On 08/11/18 08:08, Juergen Gross wrote:
>>>>> On 07/11/2018 10:30, Sander Eikelenboom wrote:
>>>>>> Hi Juergen / Boris,
>>>>>>
>>>>>> Last week i tested Linux kernel 4.19.0 stable with the Xen 
>>>>>> "for-linus-4.20" branch pulled on top.
>>>>>> Unfortunately i was seeing guests lockup after some time, see below for 
>>>>>> the logging from one of the guest
>>>>>> which i was able to capture.
>>>>>> Reverting "xen: make xen_qlock_wait() nestable" 
>>>>>> 7250f6d35681dfc44749d90598a2d51a118ce2b8,
>>>>>> made the lockups disappear.
>>>>>>
>>>>>> These guests are stressed quite hard in both CPU and networking, 
>>>>>> so they are probably more susceptible to locking issues.
>>>>>>
>>>>>> System is a AMD phenom x6, running Xen-unstable.
>>>>>>
>>>>>> Any ideas ?
>>>>>
>>>>> Just checked the hypervisor again: it seems a pending interrupt for a
>>>>> HVM/PVH vcpu won't let SCHEDOP_poll return in case interrupts are
>>>>> disabled.
>>>>>
>>>>> I need to rework the patch for that scenario. Until then I'll revert
>>>>> it.
>>>>
>>>> Thanks for looking into it.
>>>
>>> Could you try the attached patch (on top of 7250f6d35681df)?
>>
>> That blows up while booting the guest:
> 
> Oh, sorry. Of course it does. Dereferencing a percpu variable
> directly can't work. How silly of me.
> 
> The attached variant should repair that. Tested to not break booting.

This one boots. Will report back when either I find issues or
when I'm comfortable enough to give a "Tested-by" in a few days.

Thanks again.

--
Sander


> 
> Juergen
> 


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