Re: xen/evtchn: Dom0 boot hangs using preempt_rt kernel 5.10

[Luca Fancellu <luca.fancellu@xxxxxxx>]

Hi all,

I have an update, changing the lock introduced by the serie from spinlock_t to 
raw_spinlock_t, changing the lock/unlock function to use the raw_* version and 
keeping the BUG_ON(…) (now we can because raw_* implementation disable 
interrupts on preempt_rt) the kernel is booting correctly.
So seems that the BUG_ON(…) is needed and the unmask function should run with 
interrupt disabled, anyone knows why this change worked? 

> On 23 Mar 2021, at 15:39, Luca Fancellu <luca.fancellu@xxxxxxx> wrote:
> 
> Hi Jason,
> 
> Thanks for your hints, unfortunately seems not an init problem because in the 
> same init configuration I tried the 5.10.23 (preempt_rt) without the Juergen 
> patch but with the BUG_ON removed and it boots without problem. So seems that 
> applying the serie does something (on a preempt_rt kernel) and we are trying 
> to figure out what.
> 
> 
>> On 23 Mar 2021, at 12:36, Jason Andryuk <jandryuk@xxxxxxxxx> wrote:
>> 
>> On Mon, Mar 22, 2021 at 3:09 PM Luca Fancellu <luca.fancellu@xxxxxxx> wrote:
>>> 
>>> Hi Juergen,
>>> 
>>> Yes you are right it was my mistake, as you said to remove the BUG_ON(…) 
>>> this serie 
>>> (https://patchwork.kernel.org/project/xen-devel/cover/20210306161833.4552-1-jgross@xxxxxxxx/)
>>>  is needed, since I’m using yocto I’m able to build a preempt_rt kernel up 
>>> to the 5.10.23 and for this reason I’m applying that serie on top of this 
>>> version, then I’m removing the BUG_ON(…).
>>> 
>>> A thing that was not expected is that now the Dom0 kernel is stuck on 
>>> “Setting domain 0 name, domid and JSON config…” step and the system seems 
>>> unresponsive. Seems like a deadlock issue but looking into the serie we 
>>> can’t spot anything and that serie was also tested by others from the 
>>> community.
>>> Do you have any idea on that?
>> 
>> I think this can happen if xenstored isn't running.  Client access to
>> xenstore blocks until xenstored becomes available.  So check your init
>> scripts ordering.
>> 
>> Regards,
>> Jason
> 
> Cheers,
> Luca

Cheers,
Luca