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

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Message-ID: <alpine.LFD.2.00.1012142147420.12146@localhost6.localdomain6>
Date:	Tue, 14 Dec 2010 21:54:04 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jan Kiszka <jan.kiszka@....de>
cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	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>,
	Jan Kiszka <jan.kiszka@...mens.com>
Subject: Re: [PATCH v3 2/4] genirq: Inform handler about line sharing state

On Mon, 13 Dec 2010, Jan Kiszka wrote:
> @@ -943,6 +950,9 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
>  	/* Make sure it's not being used on another CPU: */
>  	synchronize_irq(irq);
>  
> +	if (single_handler)
> +		desc->irq_data.drv_status &= ~IRQS_SHARED;
> +

What's the reason to clear this flag outside of the desc->lock held
region. I need this status for other purposes as well, where I
definitely need serialization.

> +	mutex_lock(&register_lock);
> +
> +	old_action = desc->action;
> +	if (old_action && (old_action->flags & IRQF_ADAPTIVE) &&
> +	    !(desc->irq_data.drv_status & IRQS_SHARED)) {
> +		/*
> +		 * Signal the old handler that is has to switch to shareable
> +		 * handling mode. Disable the line to avoid any conflict with
> +		 * a real IRQ.
> +		 */
> +		disable_irq(irq);
> +		local_irq_disable();
> +
> +		desc->irq_data.drv_status |= IRQS_SHARED | IRQS_MAKE_SHAREABLE;

Unserialized access as well. Will think about it.

> +		old_action->handler(irq, old_action->dev_id);
> +		desc->irq_data.drv_status &= ~IRQS_MAKE_SHAREABLE;

Thanks,

	tglx
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