linux-kernel - Re: [PATCH] genirq: Fix handle_nested_irq() for IRQF

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Message-ID: <20170314144837.GZ20572@atomide.com>
Date:   Tue, 14 Mar 2017 07:48:37 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq: Fix handle_nested_irq() for IRQF_SHARED

* Thomas Gleixner <tglx@...utronix.de> [170314 01:40]:
> On Mon, 13 Mar 2017, Tony Lindgren wrote:
> 
> > Shared interrupts can be registered with handle_nested_irq(), but
> > currently only one of the registered handlers gets called.
> > 
> > The use of shared interrupts with handle_nested_irq() is probably rare,
> > but at least a case of a shared VBUS interrupt between USB PHY and
> > battery charger drivers for a PMIC makes sense.
> > 
> > Typically for_each_action_of_desc() gets called via handle_irq_event()
> > at _handle_irq_event_percpu(), but handle_nested_irq() is different
> > because of it's dummy irq_nested_primary_handler().
> > 
> > Let's fix the issue by calling the handler for all the entries in
> > the action list.
> >
> > Fixes: 399b5da29b9f ("genirq: Support nested threaded irq handling")
> 
> It's not a fix, it's an extension. The nested facility was not meant to
> handle shared interrupts in the first place. I really hope that hardware
> folks finally understand that irq sharing is crap and broken...

Yes totally.

> > +	for_each_action_of_desc(desc, action) {
> > +		action_ret = action->thread_fn(action->irq, action->dev_id);
> > +		if (!noirqdebug)
> > +			note_interrupt(desc, action_ret);
> 
> This is wrong. See how __handle_irq_event_percpu() does this. But no need
> to resend. See:
> 
> http://lkml.kernel.org/r/1488904098-5350-1-git-send-email-ckeepax@opensource.wolfsonmicro.com

Oh OK yeah makes sense, my patch is overwriting action_ret..

Thanks,

Tony