linux-kernel - Re: [PATCH v3 2/4] genirq: Inform handler about line sharing state

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Date:	Wed, 15 Dec 2010 10:48:25 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jan Kiszka <jan.kiszka@...mens.com>
cc:	Jan Kiszka <jan.kiszka@....de>, Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kvm <kvm@...r.kernel.org>, Tom Lyon <pugs@...co.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3 2/4] genirq: Inform handler about line sharing state

On Wed, 15 Dec 2010, Jan Kiszka wrote:
> Am 15.12.2010 09:05, Thomas Gleixner wrote:
> > On Wed, 15 Dec 2010, Jan Kiszka wrote:
> > 
> >> Am 14.12.2010 22:46, Thomas Gleixner wrote:
> >>> On Mon, 13 Dec 2010, Jan Kiszka wrote:
> >>>> From: Jan Kiszka <jan.kiszka@...mens.com>
> >>>>  	chip_bus_lock(desc);
> >>>>  	retval = __setup_irq(irq, desc, action);
> >>>>  	chip_bus_sync_unlock(desc);
> >>>>  
> >>>> -	if (retval)
> >>>> +	if (retval) {
> >>>> +		if (desc->action && !desc->action->next)
> >>>> +			desc->irq_data.drv_status &= ~IRQS_SHARED;
> >>>
> >>> This is redundant. IRQS_SHARED gets set in a code path where all
> >>> checks are done already.
> >>
> >> Nope, it's also set before entry of __setup_irq in case we call an
> >> IRQF_ADAPTIVE handler.
> >>
> >> We need to set it that early as we may race with IRQ events for the
> >> already registered handler happening between the sharing notification
> >> and the actual registration of the second handler.
> > 
> > Hmm, ok. Though the MAKE_SHAREABLE flag should be sufficient to do the
> > notification.
> 
> For notification, yes. But we need SHARED once we reenable the line
> after the notification.

Darn. Will think more about it.
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