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Subject: Re: [PATCH 4.4 15/97] genirq: Use irqd_get_trigger_type to compare
 the trigger type for shared IRQs
From: Ben Hutchings <ben.hutchings@codethink.co.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Hans de Goede <hdegoede@redhat.com>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Sasha Levin <alexander.levin@microsoft.com>
Date: Tue, 03 Apr 2018 15:17:16 +0100
In-Reply-To: <20180323094158.346866234@linuxfoundation.org>
References: <20180323094157.535925724@linuxfoundation.org>
         <20180323094158.346866234@linuxfoundation.org>
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On Fri, 2018-03-23 at 10:54 +0100, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Hans de Goede <hdegoede@redhat.com>
> 
> 
> [ Upstream commit 382bd4de61827dbaaf5fb4fb7b1f4be4a86505e7 ]
> 
> When requesting a shared irq with IRQF_TRIGGER_NONE then the irqaction
> flags get filled with the trigger type from the irq_data:
> 
>         if (!(new->flags & IRQF_TRIGGER_MASK))
>                 new->flags |= irqd_get_trigger_type(&desc->irq_data);

The code above was added to __setup_irq() in 4.8, so I don't think this
fix is needed in 3.18 or 4.4; and I suspect it might cause a regression
there.

Ben.

> On the first setup_irq() the trigger type in irq_data is NONE when the
> above code executes, then the irq is started up for the first time and
> then the actual trigger type gets established, but that's too late to fix
> up new->flags.
> 
> When then a second user of the irq requests the irq with IRQF_TRIGGER_NONE
> its irqaction's triggertype gets set to the actual trigger type and the
> following check fails:
> 
>         if (!((old->flags ^ new->flags) & IRQF_TRIGGER_MASK))
> 
> Resulting in the request_irq failing with -EBUSY even though both
> users requested the irq with IRQF_SHARED | IRQF_TRIGGER_NONE
> 
> Fix this by comparing the new irqaction's trigger type to the trigger type
> stored in the irq_data which correctly reflects the actual trigger type
> being used for the irq.
> 
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
> Link: http://lkml.kernel.org/r/20170415100831.17073-1-hdegoede@redhat.com
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  kernel/irq/manage.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -1189,8 +1189,10 @@ __setup_irq(unsigned int irq, struct irq
>  		 * set the trigger type must match. Also all must
>  		 * agree on ONESHOT.
>  		 */
> +		unsigned int oldtype = irqd_get_trigger_type(&desc->irq_data);
> +
>  		if (!((old->flags & new->flags) & IRQF_SHARED) ||
> -		    ((old->flags ^ new->flags) & IRQF_TRIGGER_MASK) ||
> +		    (oldtype != (new->flags & IRQF_TRIGGER_MASK)) ||
>  		    ((old->flags ^ new->flags) & IRQF_ONESHOT))
>  			goto mismatch;
>  

-- 
Ben Hutchings
Software Developer, Codethink Ltd.