linux-kernel - Re: [PATCH] IRQ: don't suspend nested

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Date:	Sat, 31 Jan 2015 00:06:37 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	NeilBrown <neilb@...e.de>, Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org,
	GTA04 owners <gta04-owner@...delico.com>,
	linux-pm@...r.kernel.org,
	Kalle Jokiniemi <kalle.jokiniemi@...lamobile.com>
Subject: Re: [PATCH] IRQ: don't suspend nested_thread irqs over system suspend.

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?

> 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@...wn.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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