linux-kernel - Re: [PATCH] genirq/manage: Reduce priority of forced secondary IRQ handler

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Message-ID: <20251024133332.wSQOgUZb@linutronix.de>
Date: Fri, 24 Oct 2025 15:33:32 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Crystal Wood <crwood@...hat.com>, Thomas Gleixner <tglx@...utronix.de>
Cc: Lukas Wunner <lukas@...ner.de>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Clark Williams <clrkwllms@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org, Attila Fazekas <afazekas@...hat.com>,
	linux-pci@...r.kernel.org, linux-rt-devel@...ts.linux.dev,
	Bjorn Helgaas <helgaas@...nel.org>,
	Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
	Oliver OHalloran <oohall@...il.com>
Subject: Re: [PATCH] genirq/manage: Reduce priority of forced secondary IRQ
 handler

On 2025-10-03 13:25:53 [-0500], Crystal Wood wrote:
> On Sun, 2025-09-21 at 15:12 +0200, Lukas Wunner wrote:
> > On Sat, Sep 20, 2025 at 11:20:26PM +0200, Thomas Gleixner wrote:
> > > I obviously understand that the proposed change squashs the whole class
> > > of similar (not yet detected) issues, but that made me look at that
> > > particular instance nevertheless.
> > > 
> > > All aer_irq() does is reading two PCI config words, writing one and then
> > > sticking 64bytes into a KFIFO. All of that is hard interrupt safe. So
> > > arguably this AER problem can be nicely solved by the below one-liner,
> > > no?
> > 
> > The one-liner (which sets IRQF_NO_THREAD) was what Crystal originally
> > proposed:
> > 
> > https://lore.kernel.org/r/20250902224441.368483-1-crwood@redhat.com/
> 
> So, is the plan to apply the original patch then?

Did we settle on something?
I wasn't sure if you can mix IRQF_NO_THREAD with IRQF_ONESHOT for shared
handlers. If that is a thing, we Crystal's original would do it. Then
there is the question if we want to go the "class" problem to ensure
that one handler can preempt the other.
And maybe I should clean up few ones tglx pointed out that provide a
primary handler for no reason…

> Thanks,
> Crystal

Sebastian