Re: [Xen-devel] [PATCH] xen/arm: Fix rtds scheduler for arm

[Denys Drozdov <denys.drozdov@xxxxxxxxxxxxxxx>]

Julien,

The details of this issue can be found in the current mailing list.
Please have a look at http://lists.xen.org/archives/html/xen-devel/2014-09/msg04250.html.

This is exactly the same behaviour we are observing when running on our arm setup.

The fix changes spin_lock_irq/spin_unlock_irq to spin_lock_irq_save/spin_lock_irq_restore,

since context_save executed right from IRQ level. The arm interrupt handling differs from x86. ARM is handling context_saved with IRQ disabled in CPSR, though x86 has IRQs on. Thus it is failing on ASSERT inside spin_lock_irq when running on ARM. I guess it should work on x86, so this issue is ARM platform specific.

On Fri, Jan 30, 2015 at 6:10 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:

On 30/01/15 15:56, Andrew Cooper wrote:
> On 30/01/15 15:46, Julien Grall wrote:
>> Hello Denys,
>>
>> On 30/01/15 15:40, Denis Drozdov wrote:
>>> From: denys drozdov <denys.drozdov@xxxxxxxxxxxxxxx>
>>>
>>> Update RT scheduler to run on arm platform
>> You need to give more background of the problem (i.e why you have to
>> disable the IRQ on ARM).
>>
>> As the scheduler is common with x86, I would expect the problem is also
>> happening on this architecture.
>
> Changing a spinlock_irq into an irqsave is safe, functionally speaking,
> but it is concerning that the scheduler appears to be called in
> different interrupt states between architectures.

For instance credit2 is also using vcpu_schedule_lock_irq... Although,
IIRC, it's not used by default. So it has to be fixed too on ARM.

In any case, the commit message needs more background such as stack
trace and/or explaining why we have to take spinlock_irq.

This may also need to document context_saved to explain the IRQs may not
be enabled when this function is called.

Regards,

--
Julien Grall

--

Denis Drozdov
GlobalLogic
M +(380)988969537Â S denis.drozdov
www.globallogic.com

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