Re: [Qemu-devel] [PATCH v3] pci: clean all funcs when hot-removing multifunc device

[Jiang Liu]

On 05/11/2012 08:24 AM, Amos Kong wrote:
> On 05/11/2012 07:54 AM, Amos Kong wrote:
>> On 05/11/2012 02:55 AM, Michael S. Tsirkin wrote:
>>> On Fri, May 11, 2012 at 01:09:13AM +0800, Jiang Liu wrote:
>>>> On 05/10/2012 11:44 PM, Amos Kong wrote:
>>>>
>>>>> diff --git a/drivers/pci/hotplug/acpiphp_glue.c 
>>>>> b/drivers/pci/hotplug/acpiphp_glue.c
>>>>> index 806c44f..a7442d9 100644
>>>>> --- a/drivers/pci/hotplug/acpiphp_glue.c
>>>>> +++ b/drivers/pci/hotplug/acpiphp_glue.c
>>>>> @@ -885,7 +885,7 @@ static void disable_bridges(struct pci_bus *bus)
>>>>>  static int disable_device(struct acpiphp_slot *slot)
>>>>>  {
>>>>>   struct acpiphp_func *func;
>>>>> - struct pci_dev *pdev;
>>>>> + struct pci_dev *pdev, *tmp;
>>>>>   struct pci_bus *bus = slot->bridge->pci_bus;
>>>>>  
>>>>>   /* The slot will be enabled when func 0 is added, so check
>>>>> @@ -902,9 +902,10 @@ static int disable_device(struct acpiphp_slot *slot)
>>>>>                   func->bridge = NULL;
>>>>>           }
>>>>>  
>>>>> -         pdev = pci_get_slot(slot->bridge->pci_bus,
>>>>> -                             PCI_DEVFN(slot->device, func->function));
>>>>> -         if (pdev) {
>>>>> +         list_for_each_entry_safe(pdev, tmp, &bus->devices, bus_list) {
>>>>> +                 if (PCI_SLOT(pdev->devfn) != slot->device)
>>>>> +                         continue;
>>>>> +
>>>> The pci_bus_sem lock should be acquired when walking the bus->devices list.
>>>> Otherwise it may cause invalid memory access if another thread is modifying
>>>> the bus->devices list concurrently.
> 
> pci_bus_sem lock is only request for writing &bus->devices list, right ?
> and this protection already exists in pci_destory_dev().
That's for writer. For reader to walk the pci_bus->devices list, you also need
to acquire the reader lock by down_read(&pci_bus_sem). Please refer to 
pci_get_slot() for example. This especially import for native OS because there
may be multiple PCI slots/devices on the bus.