linux-kernel - Re: [PATCH v3 2/3] xen/pciback: avoid multiple entries in slot list

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Date:   Thu, 22 Sep 2016 17:02:40 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Cc:     david.vrabel@...rix.com
Subject: Re: [PATCH v3 2/3] xen/pciback: avoid multiple entries in slot list

On 09/22/2016 04:45 AM, Juergen Gross wrote:
> The Xen pciback driver has a list of all pci devices it is ready to
> seize. There is no check whether a to be added entry already exists.
> While this might be no problem in the common case it might confuse
> those which consume the list via sysfs.
>
> Modify the handling of this list by not adding an entry which already
> exists. As this will be needed later split out the list handling into
> a separate function.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  drivers/xen/xen-pciback/pci_stub.c | 39 ++++++++++++++++++++++++++++++--------
>  1 file changed, 31 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index 79a9e4d..0179333 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -478,6 +478,36 @@ static int __init pcistub_init_devices_late(void)
>  	return 0;
>  }
>  
> +static void pcistub_device_id_add_list(struct pcistub_device_id *new,
> +				       int domain, int bus, unsigned int devfn)
> +{
> +	struct pcistub_device_id *pci_dev_id;
> +	unsigned long flags;
> +	int found = 0;
> +
> +	spin_lock_irqsave(&device_ids_lock, flags);
> +
> +	list_for_each_entry(pci_dev_id, &pcistub_device_ids, slot_list) {
> +		if (pci_dev_id->domain == domain && pci_dev_id->bus == bus &&
> +		    pci_dev_id->devfn == devfn) {
> +			found = 1;
> +			break;
> +		}
> +	}
> +
> +	if (!found) {
> +		new->domain = domain;
> +		new->bus = bus;
> +		new->devfn = devfn;
> +		list_add_tail(&new->slot_list, &pcistub_device_ids);
> +	}
> +
> +	spin_unlock_irqrestore(&device_ids_lock, flags);
> +
> +	if (found)
> +		kfree(new);

I'd rather free 'new' in the caller (who allocated it) and return
something like -EEXIST if device is already on the list.

-boris

> +}
> +
>  static int pcistub_seize(struct pci_dev *dev)
>  {
>  	struct pcistub_device *psdev;
> @@ -1012,7 +1042,6 @@ static inline int str_to_quirk(const char *buf, int *domain, int *bus, int
>  static int pcistub_device_id_add(int domain, int bus, int slot, int func)
>  {
>  	struct pcistub_device_id *pci_dev_id;
> -	unsigned long flags;
>  	int rc = 0, devfn = PCI_DEVFN(slot, func);
>  
>  	if (slot < 0) {
> @@ -1042,16 +1071,10 @@ static int pcistub_device_id_add(int domain, int bus, int slot, int func)
>  	if (!pci_dev_id)
>  		return -ENOMEM;
>  
> -	pci_dev_id->domain = domain;
> -	pci_dev_id->bus = bus;
> -	pci_dev_id->devfn = devfn;
> -
>  	pr_debug("wants to seize %04x:%02x:%02x.%d\n",
>  		 domain, bus, slot, func);
>  
> -	spin_lock_irqsave(&device_ids_lock, flags);
> -	list_add_tail(&pci_dev_id->slot_list, &pcistub_device_ids);
> -	spin_unlock_irqrestore(&device_ids_lock, flags);
> +	pcistub_device_id_add_list(pci_dev_id, domain, bus, devfn);
>  
>  	return 0;
>  }