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

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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On Saturday, January 31, 2015 12:06:37 AM Rafael J. Wysocki wrote:
> On Saturday, January 31, 2015 09:25:45 AM 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.  This patch does that.
> 
> Clever. :-)
> 
> This is fine by me.  Thomas, what do you think?

It looks like I've overlooked a potential problem, though.

Can a nested interrupt be a wakeup one?  We won't set IRQD_WAKEUP_ARMED for it
then and may not handle wakeup correctly.

> > This patch allows the IRQF_EARLY_RESUME to be removed from
> > twl4030_sih_setup().  That flag attempts to fix the same problem
> > is a very different way, but causes
> > 
> > [   56.095825] WARNING: CPU: 0 PID: 3 at ../kernel/irq/manage.c:661 irq_nested_primary_handler+0x18/0x28()
> > [   56.095825] Primary handler called for nested irq 348
> > 
> > warnings on resume.
> > 
> > Signed-off-by: NeilBrown <neil@brown.name>
> > 
> > diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
> > index 3ca532592704..40cbcfb7fc43 100644
> > --- a/kernel/irq/pm.c
> > +++ b/kernel/irq/pm.c
> > @@ -118,6 +118,8 @@ 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);
> > @@ -158,6 +160,8 @@ 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);
> 
> 

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.

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