Re: [PATCH] x86/xen: resume timer irqs early

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 08/08/2014 06:41 AM, David Vrabel wrote:
> On 07/08/14 18:29, Boris Ostrovsky wrote:
>> On 08/07/2014 01:16 PM, David Vrabel wrote:
>>> If the timer irqs are resumed during device resume it is possible in
>>> certain circumstances for the resume to hang early on, before device
>>> interrupts are resumed.
>>>
>>> It is not entirely clear what is occuring the point of the hang but I
>>> think a task necessary for the resume calls schedule_timeout(),
>>> waiting for a timer interrupt (which never arrives).  This failure may
>>> require specific tasks to be running on the other VCPUs to trigger
>>> (processes are not frozen during a suspend/resume if PREEMPT is
>>> disabled).
>>>
>>> Add IRQF_EARLY_RESUME to the timer interrupts so they are resumed in
>>> syscore_resume().
>>>
>>> Also add IRQF_NO_SUSPEND as it is not necessary to suspend the timer
>>> interrupts and IRQF_FORCE_RESUME was already set.
>>
>> IRQF_NO_SUSPEND is a component of IRQF_TIMER.
> So it is.  How about this instead?

The change makes sense so

     Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

but I am curious whether you actually were able to prove that it in fact 
fixes the hang (the description doesn't make it clear).

-boris


>
> 8<----------------------------
> x86/xen: resume timer irqs early
>
> If the timer irqs are resumed during device resume it is possible in
> certain circumstances for the resume to hang early on, before device
> interrupts are resumed.
>
> It is not entirely clear what is occuring the point of the hang but I
> think a task necessary for the resume calls schedule_timeout(),
> waiting for a timer interrupt (which never arrives).  This failure may
> require specific tasks to be running on the other VCPUs to trigger
> (processes are not frozen during a suspend/resume if PREEMPT is
> disabled).
>
> Add IRQF_EARLY_RESUME to the timer interrupts so they are resumed in
> syscore_resume().
>
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>   arch/x86/xen/time.c |    2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
> index 7b78f88..5718b0b 100644
> --- a/arch/x86/xen/time.c
> +++ b/arch/x86/xen/time.c
> @@ -444,7 +444,7 @@ void xen_setup_timer(int cpu)
>   
>   	irq = bind_virq_to_irqhandler(VIRQ_TIMER, cpu, xen_timer_interrupt,
>   				      IRQF_PERCPU|IRQF_NOBALANCING|IRQF_TIMER|
> -				      IRQF_FORCE_RESUME,
> +				      IRQF_FORCE_RESUME|IRQF_EARLY_RESUME,
>   				      name, NULL);
>   	(void)xen_set_irq_priority(irq, XEN_IRQ_PRIORITY_MAX);
>