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


  • To: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • From: Juergen Gross <jgross@xxxxxxxx>
  • Date: Thu, 8 Nov 2018 11:18:34 +0100
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 08 Nov 2018 10:18:47 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

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.


Juergen

Attachment: 0001-xen-fix-xen_qlock_wait.patch
Description: Text Data

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