linux-kernel - Re: [PATCH 5/5] PCI/xen-pcifront: simplify code by hotplug safe pci_get_domain_bus_and

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Date:	Wed, 29 Aug 2012 07:56:43 +0800
From:	Jiang Liu <liuj97@...il.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	Don Dutile <ddutile@...hat.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Yijing Wang <wangyijing@...wei.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH 5/5] PCI/xen-pcifront: simplify code by hotplug safe pci_get_domain_bus_and_slot()

On 08/29/2012 12:59 AM, Konrad Rzeszutek Wilk wrote:
> On Tue, Aug 28, 2012 at 11:43:58PM +0800, Jiang Liu wrote:
>> Following code has a race window between pci_find_bus() and pci_get_slot()
>> if PCI hotplug operation happens between them which removes the pci_bus.
>> So use PCI hotplug safe interface pci_get_domain_bus_and_slot() instead,
>> which also reduces code complexity.
> 
> Has this happend in practice? Is this something one can reproduce
> by manipulating SysFS and at the same time unplugging the PCI
> devices?
Hi Konrad,
	We just noticed this issue by code inspection when improving PCI
hotplug implementation. I guess we could trigger such issue by adding
some delay between pci_find_bus() and pci_get_slot().
	Regards!
	Gerry

>>
>> struct pci_bus *pci_bus = pci_find_bus(domain, busno);
>> struct pci_dev *pci_dev = pci_get_slot(pci_bus, devfn);
>>
>> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
>> ---
>>  drivers/pci/xen-pcifront.c |   10 ++--------
>>  1 file changed, 2 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/pci/xen-pcifront.c b/drivers/pci/xen-pcifront.c
>> index d6cc62c..def8d0b 100644
>> --- a/drivers/pci/xen-pcifront.c
>> +++ b/drivers/pci/xen-pcifront.c
>> @@ -982,7 +982,6 @@ static int pcifront_detach_devices(struct pcifront_device *pdev)
>>  	int err = 0;
>>  	int i, num_devs;
>>  	unsigned int domain, bus, slot, func;
>> -	struct pci_bus *pci_bus;
>>  	struct pci_dev *pci_dev;
>>  	char str[64];
>>  
>> @@ -1032,13 +1031,8 @@ static int pcifront_detach_devices(struct pcifront_device *pdev)
>>  			goto out;
>>  		}
>>  
>> -		pci_bus = pci_find_bus(domain, bus);
>> -		if (!pci_bus) {
>> -			dev_dbg(&pdev->xdev->dev, "Cannot get bus %04x:%02x\n",
>> -				domain, bus);
>> -			continue;
>> -		}
>> -		pci_dev = pci_get_slot(pci_bus, PCI_DEVFN(slot, func));
>> +		pci_dev = pci_get_domain_bus_and_slot(domain, bus,
>> +				PCI_DEVFN(slot, func));
>>  		if (!pci_dev) {
>>  			dev_dbg(&pdev->xdev->dev,
>>  				"Cannot get PCI device %04x:%02x:%02x.%d\n",
>> -- 
>> 1.7.9.5
>>

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