linux-kernel - Re: [PATCH 2/2] xen/events: increment refcnt only if event channel is refcounted

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Date: Sun, 17 Mar 2024 16:03:41 +0000
From: Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To: Juergen Gross <jgross@...e.com>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: Stefano Stabellini <sstabellini@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 2/2] xen/events: increment refcnt only if event channel is
 refcounted



On 13.03.24 09:14, Juergen Gross wrote:


Hello Juergen

> In bind_evtchn_to_irq_chip() don't increment the refcnt of the event
> channel blindly. In case the event channel is NOT refcounted, issue a
> warning instead.
> 
> Add an additional safety net by doing the refcnt increment only if the
> caller has specified IRQF_SHARED in the irqflags parameter.
> 
> Fixes: 9e90e58c11b7 ("xen: evtchn: Allow shared registration of IRQ handers")
> Signed-off-by: Juergen Gross <jgross@...e.com>


Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>


> ---
>   drivers/xen/events/events_base.c | 22 +++++++++++++---------
>   1 file changed, 13 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index 2faa4bf78c7a..81effbd53dc5 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -1190,7 +1190,7 @@ int xen_pirq_from_irq(unsigned irq)
>   EXPORT_SYMBOL_GPL(xen_pirq_from_irq);
>   
>   static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
> -				   struct xenbus_device *dev)
> +				   struct xenbus_device *dev, bool shared)
>   {
>   	int ret = -ENOMEM;
>   	struct irq_info *info;
> @@ -1224,7 +1224,8 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
>   		 */
>   		bind_evtchn_to_cpu(info, 0, false);
>   	} else if (!WARN_ON(info->type != IRQT_EVTCHN)) {
> -		info->refcnt++;
> +		if (shared && !WARN_ON(info->refcnt < 0))
> +			info->refcnt++;
>   	}
>   
>   	ret = info->irq;
> @@ -1237,13 +1238,13 @@ static int bind_evtchn_to_irq_chip(evtchn_port_t evtchn, struct irq_chip *chip,
>   
>   int bind_evtchn_to_irq(evtchn_port_t evtchn)
>   {
> -	return bind_evtchn_to_irq_chip(evtchn, &xen_dynamic_chip, NULL);
> +	return bind_evtchn_to_irq_chip(evtchn, &xen_dynamic_chip, NULL, false);
>   }
>   EXPORT_SYMBOL_GPL(bind_evtchn_to_irq);
>   
>   int bind_evtchn_to_irq_lateeoi(evtchn_port_t evtchn)
>   {
> -	return bind_evtchn_to_irq_chip(evtchn, &xen_lateeoi_chip, NULL);
> +	return bind_evtchn_to_irq_chip(evtchn, &xen_lateeoi_chip, NULL, false);
>   }
>   EXPORT_SYMBOL_GPL(bind_evtchn_to_irq_lateeoi);
>   
> @@ -1295,7 +1296,8 @@ static int bind_ipi_to_irq(unsigned int ipi, unsigned int cpu)
>   
>   static int bind_interdomain_evtchn_to_irq_chip(struct xenbus_device *dev,
>   					       evtchn_port_t remote_port,
> -					       struct irq_chip *chip)
> +					       struct irq_chip *chip,
> +					       bool shared)
>   {
>   	struct evtchn_bind_interdomain bind_interdomain;
>   	int err;
> @@ -1307,14 +1309,14 @@ static int bind_interdomain_evtchn_to_irq_chip(struct xenbus_device *dev,
>   					  &bind_interdomain);
>   
>   	return err ? : bind_evtchn_to_irq_chip(bind_interdomain.local_port,
> -					       chip, dev);
> +					       chip, dev, shared);
>   }
>   
>   int bind_interdomain_evtchn_to_irq_lateeoi(struct xenbus_device *dev,
>   					   evtchn_port_t remote_port)
>   {
>   	return bind_interdomain_evtchn_to_irq_chip(dev, remote_port,
> -						   &xen_lateeoi_chip);
> +						   &xen_lateeoi_chip, false);
>   }
>   EXPORT_SYMBOL_GPL(bind_interdomain_evtchn_to_irq_lateeoi);
>   
> @@ -1430,7 +1432,8 @@ static int bind_evtchn_to_irqhandler_chip(evtchn_port_t evtchn,
>   {
>   	int irq, retval;
>   
> -	irq = bind_evtchn_to_irq_chip(evtchn, chip, NULL);
> +	irq = bind_evtchn_to_irq_chip(evtchn, chip, NULL,
> +				      irqflags & IRQF_SHARED);
>   	if (irq < 0)
>   		return irq;
>   	retval = request_irq(irq, handler, irqflags, devname, dev_id);
> @@ -1471,7 +1474,8 @@ static int bind_interdomain_evtchn_to_irqhandler_chip(
>   {
>   	int irq, retval;
>   
> -	irq = bind_interdomain_evtchn_to_irq_chip(dev, remote_port, chip);
> +	irq = bind_interdomain_evtchn_to_irq_chip(dev, remote_port, chip,
> +						  irqflags & IRQF_SHARED);
>   	if (irq < 0)
>   		return irq;
>