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Date:   Tue, 27 Feb 2018 17:07:40 +0000
From:   Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau@citrix.com>
To:     Amit Shah <aams@amazon.com>
CC:     <xen-devel@lists.xenproject.org>, <linux-kernel@vger.kernel.org>,
        <stable@vger.kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Eduardo Valentin <eduval@amazon.com>,
        Juergen Gross <jgross@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Liu Shuo <shuo.a.liu@intel.com>,
        Anoob Soman <anoob.soman@citrix.com>
Subject: Re: [PATCH v2 2/2] xen: events: free irqs in error condition
Message-ID: <20180227170740.jcaxsvpepsn6eot2@MacBook-Pro-de-Roger.local>
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On Tue, Feb 27, 2018 at 03:55:58PM +0000, Amit Shah wrote:
> In case of errors in irq setup for MSI, free up the allocated irqs.
> 
> Fixes: 4892c9b4ada9f9 ("xen: add support for MSI message groups")
> Reported-by: Hooman Mirhadi <mirhadih@amazon.com>
> CC: <stable@vger.kernel.org>
> CC: Roger Pau Monn? <roger.pau@citrix.com>
> CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> CC: Eduardo Valentin <eduval@amazon.com>
> CC: Juergen Gross <jgross@suse.com>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Liu Shuo <shuo.a.liu@intel.com>
> CC: Anoob Soman <anoob.soman@citrix.com>
> Signed-off-by: Amit Shah <aams@amazon.com>
> ---
>  drivers/xen/events/events_base.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> index c86d10e..a299586 100644
> --- a/drivers/xen/events/events_base.c
> +++ b/drivers/xen/events/events_base.c
> @@ -750,11 +750,14 @@ int xen_bind_pirq_msi_to_irq(struct pci_dev *dev, struct msi_desc *msidesc,
>  
>  	ret = irq_set_msi_desc(irq, msidesc);
>  	if (ret < 0)
> -		goto error_irq;
> +		goto error_desc;
>  out:
>  	mutex_unlock(&irq_mapping_update_lock);
>  	return irq;
>  error_irq:
> +	while (--nvec >= i)
> +		xen_free_irq(irq + nvec);
> +error_desc:
>  	while (i > 0) {
>  		i--;
>  		__unbind_from_irq(irq + i);

It seems pointless to introduce another label and another loop to fix
something that can be fixed with a single label and a single loop,
this just makes the code more complex for no reason.

IMHO the way to solve this issue is:

while (nvec--) {
	if (nvec >= i)
		xen_free_irq(irq + nvec);
	else
		__unbind_from_irq(irq + nvec);
}

Roger.