linux-kernel - Re: [PATCH 2/2] genirq: Retain disable depth across irq shutdown/startup

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Message-ID: <aCT6I5dhx5-xluOo@google.com>
Date: Wed, 14 May 2025 13:16:35 -0700
From: Brian Norris <briannorris@...omium.org>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Douglas Anderson <dianders@...omium.org>,
	Tsai Sung-Fu <danielsftsai@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] genirq: Retain disable depth across irq
 shutdown/startup

Hi Thomas,

On Wed, May 14, 2025 at 09:35:49AM +0200, Thomas Gleixner wrote:
> On Tue, May 13 2025 at 15:42, Brian Norris wrote:
> > @@ -272,7 +272,9 @@ int irq_startup(struct irq_desc *desc, bool resend, bool force)
> >  	const struct cpumask *aff = irq_data_get_affinity_mask(d);
> >  	int ret = 0;
> >  
> > -	desc->depth = 0;
> > +	desc->depth--;
> > +	if (desc->depth)
> > +		return 0;
> 
> This breaks a
> 
>      request_irq()
>      disable_irq()
>      free_irq()
>      request_irq()
> 
> sequence.

Ah, thanks for the callout. I factored that into another unit test in
v2.

> So the only case where the disable depth needs to be preserved is for
> managed interrupts in the hotunplug -> shutdown -> hotplug -> startup
> scenario. Making that explicit avoids chasing all other places and
> sprinkle desc->depth = 1 into them. Something like the uncompiled below
> should do the trick.

Seems reasonable, and it works for me. I've incorporated that in v2,
although I'm not sure how the attribution should work there.

Thanks,
Brian