Re: [PATCH - RE-RESEND] IRQ: don't suspend nested_thread irqs over system suspend.

[Peter Zijlstra <peterz@infradead.org>]

On Sun, May 17, 2015 at 03:19:34PM +1000, NeilBrown wrote:
> 
> 
> Nested IRQs can only fire when the parent irq fires.
> So when the parent is suspended, there is no need to suspend
> the child irq.
> 
> Suspending nested irqs can cause a problem is they are suspended or
> resumed in the wrong order.
> If an interrupt fires while the parent is active but the child is
> suspended, then the interrupt will not be acknowledged properly
> and so an interrupt storm can result.
> This is particularly likely if the parent is resumed before
> the child, and the interrupt was raised during suspend.
> 
> Ensuring correct ordering would be possible, but it is simpler
> to just never suspend nested interrupts.

Looks sane to me, but it's Thomas' call.

FWIW:

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>

> 
> Signed-off-by: NeilBrown <neil@brown.name>
> ---
> diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
> index 5204a6d1b985..d22786a6dbde 100644
> --- a/kernel/irq/pm.c
> +++ b/kernel/irq/pm.c
> @@ -123,6 +123,8 @@ void suspend_device_irqs(void)
>  		unsigned long flags;
>  		bool sync;
>  
> +		if (irq_settings_is_nested_thread(desc))
> +			continue;
>  		raw_spin_lock_irqsave(&desc->lock, flags);
>  		sync = suspend_device_irq(desc, irq);
>  		raw_spin_unlock_irqrestore(&desc->lock, flags);
> @@ -163,6 +165,8 @@ static void resume_irqs(bool want_early)
>  
>  		if (!is_early && want_early)
>  			continue;
> +		if (irq_settings_is_nested_thread(desc))
> +			continue;
>  
>  		raw_spin_lock_irqsave(&desc->lock, flags);
>  		resume_irq(desc, irq);