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

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Message-ID: <1784621.LW7069gAjl@vostro.rjw.lan>
Date:	Sat, 16 May 2015 02:31:52 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	NeilBrown <neilb@...e.de>
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	GTA04 owners <gta04-owner@...delico.com>,
	linux-pm@...r.kernel.org,
	Kalle Jokiniemi <kalle.jokiniemi@...lamobile.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH - RESEND] IRQ: don't suspend nested_thread irqs over system suspend.

On Tuesday, February 24, 2015 01:28:05 PM NeilBrown wrote:
> 
> --Sig_/GFnrHDc1Bs/XVRdbvRQTN5O
> Content-Type: text/plain; charset=US-ASCII
> Content-Transfer-Encoding: quoted-printable
> 
> 
> 
> 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.
> 
> Signed-off-by: NeilBrown <neil@...wn.name>

We need to make some progress here.

Can you please resend it again for people to have a fresh look (and CC PeterZ
this time too)?

> 
> ---
> This is a resend of a patch sent at the end of January 2015.
> Rafael seemed happy with it, but I receive no other response so I'm resendi=
> ng.
> 
> Thanks,
> NeilBrown
> 
> 
> 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;
> =20
> +		if (irq_settings_is_nested_thread(desc))
> +			continue;
>  		raw_spin_lock_irqsave(&desc->lock, flags);
>  		sync =3D suspend_device_irq(desc, irq);
>  		raw_spin_unlock_irqrestore(&desc->lock, flags);
> @@ -158,6 +160,8 @@ static void resume_irqs(bool want_early)
> =20
>  		if (!is_early && want_early)
>  			continue;
> +		if (irq_settings_is_nested_thread(desc))
> +			continue;
> =20
>  		raw_spin_lock_irqsave(&desc->lock, flags);
>  		resume_irq(desc, irq);
> 
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-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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